diff options
Diffstat (limited to 'Documentation/kbuild')
| -rw-r--r-- | Documentation/kbuild/Kconfig.recursion-issue-02 | 4 | ||||
| -rw-r--r-- | Documentation/kbuild/gcc-plugins.rst | 133 | ||||
| -rw-r--r-- | Documentation/kbuild/index.rst | 2 | ||||
| -rw-r--r-- | Documentation/kbuild/kbuild.rst | 56 | ||||
| -rw-r--r-- | Documentation/kbuild/kconfig-language.rst | 151 | ||||
| -rw-r--r-- | Documentation/kbuild/kconfig-macro-language.rst | 4 | ||||
| -rw-r--r-- | Documentation/kbuild/kconfig.rst | 32 | ||||
| -rw-r--r-- | Documentation/kbuild/llvm.rst | 222 | ||||
| -rw-r--r-- | Documentation/kbuild/makefiles.rst | 2225 | ||||
| -rw-r--r-- | Documentation/kbuild/modules.rst | 21 | ||||
| -rw-r--r-- | Documentation/kbuild/reproducible-builds.rst | 18 |
11 files changed, 1778 insertions, 1090 deletions
diff --git a/Documentation/kbuild/Kconfig.recursion-issue-02 b/Documentation/kbuild/Kconfig.recursion-issue-02 index b9fd56c4b57e..09dcb92d9b43 100644 --- a/Documentation/kbuild/Kconfig.recursion-issue-02 +++ b/Documentation/kbuild/Kconfig.recursion-issue-02 @@ -6,7 +6,7 @@ # make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-02 allnoconfig # # The recursive limitations with Kconfig has some non intuitive implications on -# kconfig sematics which are documented here. One known practical implication +# kconfig semantics which are documented here. One known practical implication # of the recursive limitation is that drivers cannot negate features from other # drivers if they share a common core requirement and use disjoint semantics to # annotate those requirements, ie, some drivers use "depends on" while others @@ -42,7 +42,7 @@ # "select FW_LOADER" [0], in the end the simple alternative solution to this # problem consisted on matching semantics with newly introduced features. # -# [0] http://lkml.kernel.org/r/1432241149-8762-1-git-send-email-mcgrof@do-not-panic.com +# [0] https://lore.kernel.org/r/1432241149-8762-1-git-send-email-mcgrof@do-not-panic.com mainmenu "Simple example to demo cumulative kconfig recursive dependency implication" diff --git a/Documentation/kbuild/gcc-plugins.rst b/Documentation/kbuild/gcc-plugins.rst new file mode 100644 index 000000000000..c578c6ba3eb6 --- /dev/null +++ b/Documentation/kbuild/gcc-plugins.rst @@ -0,0 +1,133 @@ +========================= +GCC plugin infrastructure +========================= + + +Introduction +============ + +GCC plugins are loadable modules that provide extra features to the +compiler [1]_. They are useful for runtime instrumentation and static analysis. +We can analyse, change and add further code during compilation via +callbacks [2]_, GIMPLE [3]_, IPA [4]_ and RTL passes [5]_. + +The GCC plugin infrastructure of the kernel supports building out-of-tree +modules, cross-compilation and building in a separate directory. +Plugin source files have to be compilable by a C++ compiler. + +Currently the GCC plugin infrastructure supports only some architectures. +Grep "select HAVE_GCC_PLUGINS" to find out which architectures support +GCC plugins. + +This infrastructure was ported from grsecurity [6]_ and PaX [7]_. + +-- + +.. [1] https://gcc.gnu.org/onlinedocs/gccint/Plugins.html +.. [2] https://gcc.gnu.org/onlinedocs/gccint/Plugin-API.html#Plugin-API +.. [3] https://gcc.gnu.org/onlinedocs/gccint/GIMPLE.html +.. [4] https://gcc.gnu.org/onlinedocs/gccint/IPA.html +.. [5] https://gcc.gnu.org/onlinedocs/gccint/RTL.html +.. [6] https://grsecurity.net/ +.. [7] https://pax.grsecurity.net/ + + +Purpose +======= + +GCC plugins are designed to provide a place to experiment with potential +compiler features that are neither in GCC nor Clang upstream. Once +their utility is proven, the goal is to upstream the feature into GCC +(and Clang), and then to finally remove them from the kernel once the +feature is available in all supported versions of GCC. + +Specifically, new plugins should implement only features that have no +upstream compiler support (in either GCC or Clang). + +When a feature exists in Clang but not GCC, effort should be made to +bring the feature to upstream GCC (rather than just as a kernel-specific +GCC plugin), so the entire ecosystem can benefit from it. + +Similarly, even if a feature provided by a GCC plugin does *not* exist +in Clang, but the feature is proven to be useful, effort should be spent +to upstream the feature to GCC (and Clang). + +After a feature is available in upstream GCC, the plugin will be made +unbuildable for the corresponding GCC version (and later). Once all +kernel-supported versions of GCC provide the feature, the plugin will +be removed from the kernel. + + +Files +===== + +**$(src)/scripts/gcc-plugins** + + This is the directory of the GCC plugins. + +**$(src)/scripts/gcc-plugins/gcc-common.h** + + This is a compatibility header for GCC plugins. + It should be always included instead of individual gcc headers. + +**$(src)/scripts/gcc-plugins/gcc-generate-gimple-pass.h, +$(src)/scripts/gcc-plugins/gcc-generate-ipa-pass.h, +$(src)/scripts/gcc-plugins/gcc-generate-simple_ipa-pass.h, +$(src)/scripts/gcc-plugins/gcc-generate-rtl-pass.h** + + These headers automatically generate the registration structures for + GIMPLE, SIMPLE_IPA, IPA and RTL passes. + They should be preferred to creating the structures by hand. + + +Usage +===== + +You must install the gcc plugin headers for your gcc version, +e.g., on Ubuntu for gcc-10:: + + apt-get install gcc-10-plugin-dev + +Or on Fedora:: + + dnf install gcc-plugin-devel libmpc-devel + +Or on Fedora when using cross-compilers that include plugins:: + + dnf install libmpc-devel + +Enable the GCC plugin infrastructure and some plugin(s) you want to use +in the kernel config:: + + CONFIG_GCC_PLUGINS=y + CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y + ... + +Run gcc (native or cross-compiler) to ensure plugin headers are detected:: + + gcc -print-file-name=plugin + CROSS_COMPILE=arm-linux-gnu- ${CROSS_COMPILE}gcc -print-file-name=plugin + +The word "plugin" means they are not detected:: + + plugin + +A full path means they are detected:: + + /usr/lib/gcc/x86_64-redhat-linux/12/plugin + +To compile the minimum tool set including the plugin(s):: + + make scripts + +or just run the kernel make and compile the whole kernel with +the cyclomatic complexity GCC plugin. + + +4. How to add a new GCC plugin +============================== + +The GCC plugins are in scripts/gcc-plugins/. You need to put plugin source files +right under scripts/gcc-plugins/. Creating subdirectories is not supported. +It must be added to scripts/gcc-plugins/Makefile, scripts/Makefile.gcc-plugins +and a relevant Kconfig file. diff --git a/Documentation/kbuild/index.rst b/Documentation/kbuild/index.rst index 0f144fad99a6..cee2f99f734b 100644 --- a/Documentation/kbuild/index.rst +++ b/Documentation/kbuild/index.rst @@ -19,6 +19,8 @@ Kernel Build System issues reproducible-builds + gcc-plugins + llvm .. only:: subproject and html diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst index f1e5dce86af7..9c8d1d046ea5 100644 --- a/Documentation/kbuild/kbuild.rst +++ b/Documentation/kbuild/kbuild.rst @@ -48,6 +48,10 @@ KCFLAGS ------- Additional options to the C compiler (for built-in and modules). +KRUSTFLAGS +---------- +Additional options to the Rust compiler (for built-in and modules). + CFLAGS_KERNEL ------------- Additional options for $(CC) when used to compile @@ -57,6 +61,15 @@ CFLAGS_MODULE ------------- Additional module specific options to use for $(CC). +RUSTFLAGS_KERNEL +---------------- +Additional options for $(RUSTC) when used to compile +code that is compiled as built-in. + +RUSTFLAGS_MODULE +---------------- +Additional module specific options to use for $(RUSTC). + LDFLAGS_MODULE -------------- Additional options used for $(LD) when linking modules. @@ -69,6 +82,10 @@ HOSTCXXFLAGS ------------ Additional flags to be passed to $(HOSTCXX) when building host programs. +HOSTRUSTFLAGS +------------- +Additional flags to be passed to $(HOSTRUSTC) when building host programs. + HOSTLDFLAGS ----------- Additional flags to be passed when linking host programs. @@ -77,6 +94,17 @@ HOSTLDLIBS ---------- Additional libraries to link against when building host programs. +.. _userkbuildflags: + +USERCFLAGS +---------- +Additional options used for $(CC) when compiling userprogs. + +USERLDFLAGS +----------- +Additional options used for $(LD) when linking userprogs. userprogs are linked +with CC, so $(USERLDFLAGS) should include "-Wl," prefix as applicable. + KBUILD_KCONFIG -------------- Set the top-level Kconfig file to the value of this environment @@ -122,6 +150,12 @@ the UTS_MACHINE variable, and on some architectures also the kernel config. The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian architecture. +KDOCFLAGS +--------- +Specify extra (warning/error) flags for kernel-doc checks during the build, +see scripts/kernel-doc for which flags are supported. Note that this doesn't +(currently) apply to documentation builds. + ARCH ---- Set ARCH to the architecture to be built. @@ -132,7 +166,7 @@ directory name found in the arch/ directory. But some architectures such as x86 and sparc have aliases. - x86: i386 for 32 bit, x86_64 for 64 bit -- sh: sh for 32 bit, sh64 for 64 bit +- parisc: parisc64 for 64 bit - sparc: sparc32 for 32 bit, sparc64 for 64 bit CROSS_COMPILE @@ -209,6 +243,12 @@ The output directory is often set using "O=..." on the commandline. The value can be overridden in which case the default value is ignored. +INSTALL_DTBS_PATH +----------------- +INSTALL_DTBS_PATH specifies where to install device tree blobs for +relocations required by build roots. This is not defined in the +makefile but the argument can be passed to make if needed. + KBUILD_ABS_SRCTREE -------------------------------------------------- Kbuild uses a relative path to point to the tree when possible. For instance, @@ -237,7 +277,7 @@ This is solely useful to speed up test compiles. KBUILD_EXTRA_SYMBOLS -------------------- For modules that use symbols from other modules. -See more details in modules.txt. +See more details in modules.rst. ALLSOURCE_ARCHS --------------- @@ -250,6 +290,13 @@ To get all available archs you can also specify all. E.g.:: $ make ALLSOURCE_ARCHS=all tags +IGNORE_DIRS +----------- +For tags/TAGS/cscope targets, you can choose which directories won't +be included in the databases, separated by blank space. E.g.:: + + $ make IGNORE_DIRS="drivers/gpu/drm/radeon tools" cscope + KBUILD_BUILD_TIMESTAMP ---------------------- Setting this to a date string overrides the timestamp used in the @@ -262,3 +309,8 @@ KBUILD_BUILD_USER, KBUILD_BUILD_HOST These two variables allow to override the user@host string displayed during boot and in /proc/version. The default value is the output of the commands whoami and host, respectively. + +LLVM +---- +If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead +of GCC and GNU binutils to build the kernel. diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst index 74bef19f69f0..0135905c0aa3 100644 --- a/Documentation/kbuild/kconfig-language.rst +++ b/Documentation/kbuild/kconfig-language.rst @@ -159,11 +159,11 @@ applicable everywhere (see syntax). Given the following example:: config FOO - tristate + tristate "foo" imply BAZ config BAZ - tristate + tristate "baz" depends on BAR The following values are possible: @@ -173,7 +173,10 @@ applicable everywhere (see syntax). === === ============= ============== n y n N/m/y m y m M/y/n - y y y Y/n + y y y Y/m/n + n m n N/m + m m m M/n + y m m M/n y n * N === === ============= ============== @@ -181,6 +184,24 @@ applicable everywhere (see syntax). ability to hook into a secondary subsystem while allowing the user to configure that subsystem out without also having to unset these drivers. + Note: If the combination of FOO=y and BAR=m causes a link error, + you can guard the function call with IS_REACHABLE():: + + foo_init() + { + if (IS_REACHABLE(CONFIG_BAZ)) + baz_register(&foo); + ... + } + + Note: If the feature provided by BAZ is highly desirable for FOO, + FOO should imply not only BAZ, but also its dependency BAR:: + + config FOO + tristate "foo" + imply BAR + imply BAZ + - limiting menu display: "visible if" <expr> This attribute is only applicable to menu blocks, if the condition is @@ -196,34 +217,16 @@ applicable everywhere (see syntax). or equal to the first symbol and smaller than or equal to the second symbol. -- help text: "help" or "---help---" +- help text: "help" This defines a help text. The end of the help text is determined by the indentation level, this means it ends at the first line which has a smaller indentation than the first line of the help text. - "---help---" and "help" do not differ in behaviour, "---help---" is - used to help visually separate configuration logic from help within - the file as an aid to developers. -- misc options: "option" <symbol>[=<value>] - - Various less common options can be defined via this option syntax, - which can modify the behaviour of the menu entry and its config - symbol. These options are currently possible: - - - "defconfig_list" - This declares a list of default entries which can be used when - looking for the default configuration (which is used when the main - .config doesn't exists yet.) - - - "modules" - This declares the symbol to be used as the MODULES symbol, which - enables the third modular state for all config symbols. - At most one symbol may have the "modules" option set. - - - "allnoconfig_y" - This declares the symbol as one that should have the value y when - using "allnoconfig". Used for symbols that hide other symbols. +- module attribute: "modules" + This declares the symbol to be used as the MODULES symbol, which + enables the third modular state for all config symbols. + At most one symbol may have the "modules" option set. Menu dependencies ----------------- @@ -522,8 +525,8 @@ followed by a test macro:: If you need to expose a compiler capability to makefiles and/or C source files, `CC_HAS_` is the recommended prefix for the config option:: - config CC_HAS_STACKPROTECTOR_NONE - def_bool $(cc-option,-fno-stack-protector) + config CC_HAS_FOO + def_bool $(success,$(srctree)/scripts/cc-check-foo.sh $(CC)) Build as module only ~~~~~~~~~~~~~~~~~~~~ @@ -535,6 +538,67 @@ with "depends on m". E.g.:: limits FOO to module (=m) or disabled (=n). +Compile-testing +~~~~~~~~~~~~~~~ +If a config symbol has a dependency, but the code controlled by the config +symbol can still be compiled if the dependency is not met, it is encouraged to +increase build coverage by adding an "|| COMPILE_TEST" clause to the +dependency. This is especially useful for drivers for more exotic hardware, as +it allows continuous-integration systems to compile-test the code on a more +common system, and detect bugs that way. +Note that compile-tested code should avoid crashing when run on a system where +the dependency is not met. + +Architecture and platform dependencies +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Due to the presence of stubs, most drivers can now be compiled on most +architectures. However, this does not mean it makes sense to have all drivers +available everywhere, as the actual hardware may only exist on specific +architectures and platforms. This is especially true for on-SoC IP cores, +which may be limited to a specific vendor or SoC family. + +To prevent asking the user about drivers that cannot be used on the system(s) +the user is compiling a kernel for, and if it makes sense, config symbols +controlling the compilation of a driver should contain proper dependencies, +limiting the visibility of the symbol to (a superset of) the platform(s) the +driver can be used on. The dependency can be an architecture (e.g. ARM) or +platform (e.g. ARCH_OMAP4) dependency. This makes life simpler not only for +distro config owners, but also for every single developer or user who +configures a kernel. + +Such a dependency can be relaxed by combining it with the compile-testing rule +above, leading to: + + config FOO + bool "Support for foo hardware" + depends on ARCH_FOO_VENDOR || COMPILE_TEST + +Optional dependencies +~~~~~~~~~~~~~~~~~~~~~ + +Some drivers are able to optionally use a feature from another module +or build cleanly with that module disabled, but cause a link failure +when trying to use that loadable module from a built-in driver. + +The most common way to express this optional dependency in Kconfig logic +uses the slightly counterintuitive:: + + config FOO + tristate "Support for foo hardware" + depends on BAR || !BAR + +This means that there is either a dependency on BAR that disallows +the combination of FOO=y with BAR=m, or BAR is completely disabled. +For a more formalized approach if there are multiple drivers that have +the same dependency, a helper symbol can be used, like:: + + config FOO + tristate "Support for foo hardware" + depends on BAR_OPTIONAL + + config BAR_OPTIONAL + def_tristate BAR || !BAR + Kconfig recursive dependency limitations ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -594,7 +658,8 @@ The two different resolutions for b) can be tested in the sample Kconfig file Documentation/kbuild/Kconfig.recursion-issue-02. Below is a list of examples of prior fixes for these types of recursive issues; -all errors appear to involve one or more select's and one or more "depends on". +all errors appear to involve one or more "select" statements and one or more +"depends on". ============ =================================== commit fix @@ -633,7 +698,7 @@ Future kconfig work Work on kconfig is welcomed on both areas of clarifying semantics and on evaluating the use of a full SAT solver for it. A full SAT solver can be desirable to enable more complex dependency mappings and / or queries, -for instance on possible use case for a SAT solver could be that of handling +for instance one possible use case for a SAT solver could be that of handling the current known recursive dependency issues. It is not known if this would address such issues but such evaluation is desirable. If support for a full SAT solver proves too complex or that it cannot address recursive dependency issues @@ -654,25 +719,29 @@ in documenting basic Kconfig syntax a more precise definition of Kconfig semantics is welcomed. One project deduced Kconfig semantics through the use of the xconfig configurator [1]_. Work should be done to confirm if the deduced semantics matches our intended Kconfig design goals. +Another project formalized a denotational semantics of a core subset of +the Kconfig language [10]_. Having well defined semantics can be useful for tools for practical -evaluation of depenencies, for instance one such use known case was work to +evaluation of dependencies, for instance one such case was work to express in boolean abstraction of the inferred semantics of Kconfig to translate Kconfig logic into boolean formulas and run a SAT solver on this to find dead code / features (always inactive), 114 dead features were found in Linux using this methodology [1]_ (Section 8: Threats to validity). +The kismet tool, based on the semantics in [10]_, finds abuses of reverse +dependencies and has led to dozens of committed fixes to Linux Kconfig files [11]_. -Confirming this could prove useful as Kconfig stands as one of the the leading +Confirming this could prove useful as Kconfig stands as one of the leading industrial variability modeling languages [1]_ [2]_. Its study would help evaluate practical uses of such languages, their use was only theoretical and real world requirements were not well understood. As it stands though only reverse engineering techniques have been used to deduce semantics from variability modeling languages such as Kconfig [3]_. -.. [0] http://www.eng.uwaterloo.ca/~shshe/kconfig_semantics.pdf -.. [1] http://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf -.. [2] http://gsd.uwaterloo.ca/sites/default/files/ase241-berger_0.pdf -.. [3] http://gsd.uwaterloo.ca/sites/default/files/icse2011.pdf +.. [0] https://www.eng.uwaterloo.ca/~shshe/kconfig_semantics.pdf +.. [1] https://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf +.. [2] https://gsd.uwaterloo.ca/sites/default/files/ase241-berger_0.pdf +.. [3] https://gsd.uwaterloo.ca/sites/default/files/icse2011.pdf Full SAT solver for Kconfig ~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -683,7 +752,7 @@ abstraction the inferred semantics of Kconfig to translate Kconfig logic into boolean formulas and run a SAT solver on it [5]_. Another known related project is CADOS [6]_ (former VAMOS [7]_) and the tools, mainly undertaker [8]_, which has been introduced first with [9]_. The basic concept of undertaker is to -exract variability models from Kconfig, and put them together with a +extract variability models from Kconfig and put them together with a propositional formula extracted from CPP #ifdefs and build-rules into a SAT solver in order to find dead code, dead files, and dead symbols. If using a SAT solver is desirable on Kconfig one approach would be to evaluate repurposing @@ -691,11 +760,13 @@ such efforts somehow on Kconfig. There is enough interest from mentors of existing projects to not only help advise how to integrate this work upstream but also help maintain it long term. Interested developers should visit: -http://kernelnewbies.org/KernelProjects/kconfig-sat +https://kernelnewbies.org/KernelProjects/kconfig-sat -.. [4] http://www.cs.cornell.edu/~sabhar/chapters/SATSolvers-KR-Handbook.pdf -.. [5] http://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf +.. [4] https://www.cs.cornell.edu/~sabhar/chapters/SATSolvers-KR-Handbook.pdf +.. [5] https://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf .. [6] https://cados.cs.fau.de .. [7] https://vamos.cs.fau.de .. [8] https://undertaker.cs.fau.de .. [9] https://www4.cs.fau.de/Publications/2011/tartler_11_eurosys.pdf +.. [10] https://paulgazzillo.com/papers/esecfse21.pdf +.. [11] https://github.com/paulgazz/kmax diff --git a/Documentation/kbuild/kconfig-macro-language.rst b/Documentation/kbuild/kconfig-macro-language.rst index 35b3263b7e40..6163467f6ae4 100644 --- a/Documentation/kbuild/kconfig-macro-language.rst +++ b/Documentation/kbuild/kconfig-macro-language.rst @@ -44,7 +44,7 @@ intermediate:: def_bool y Then, Kconfig moves onto the evaluation stage to resolve inter-symbol -dependency as explained in kconfig-language.txt. +dependency as explained in kconfig-language.rst. Variables @@ -97,7 +97,7 @@ Like Make, Kconfig provides several built-in functions. Every function takes a particular number of arguments. In Make, every built-in function takes at least one argument. Kconfig allows -zero argument for built-in functions, such as $(fileno), $(lineno). You could +zero argument for built-in functions, such as $(filename), $(lineno). You could consider those as "built-in variable", but it is just a matter of how we call it after all. Let's say "built-in function" here to refer to natively supported functionality. diff --git a/Documentation/kbuild/kconfig.rst b/Documentation/kbuild/kconfig.rst index a9a855f894b3..c946eb44bd13 100644 --- a/Documentation/kbuild/kconfig.rst +++ b/Documentation/kbuild/kconfig.rst @@ -10,6 +10,8 @@ The xconfig ('qconf'), menuconfig ('mconf'), and nconfig ('nconf') programs also have embedded help text. Be sure to check that for navigation, search, and other general help text. +The gconfig ('gconf') program has limited help text. + General ------- @@ -41,11 +43,28 @@ KCONFIG_CONFIG This environment variable can be used to specify a default kernel config file name to override the default name of ".config". +KCONFIG_DEFCONFIG_LIST +---------------------- + +This environment variable specifies a list of config files which can be used +as a base configuration in case the .config does not exist yet. Entries in +the list are separated with whitespaces to each other, and the first one +that exists is used. + KCONFIG_OVERWRITECONFIG ----------------------- If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not break symlinks when .config is a symlink to somewhere else. +KCONFIG_WARN_UNKNOWN_SYMBOLS +---------------------------- +This environment variable makes Kconfig warn about all unrecognized +symbols in the config input. + +KCONFIG_WERROR +-------------- +If set, Kconfig treats warnings as errors. + `CONFIG_` --------- If you set `CONFIG_` in the environment, Kconfig will prefix all symbols @@ -154,11 +173,6 @@ KCONFIG_AUTOCONFIG This environment variable can be set to specify the path & name of the "auto.conf" file. Its default value is "include/config/auto.conf". -KCONFIG_TRISTATE ----------------- -This environment variable can be set to specify the path & name of the -"tristate.conf" file. Its default value is "include/config/tristate.conf". - KCONFIG_AUTOHEADER ------------------ This environment variable can be set to specify the path & name of the @@ -207,6 +221,10 @@ Searching in menuconfig: first (and in alphabetical order), then come all other symbols, sorted in alphabetical order. + In this menu, pressing the key in the (#) prefix will jump + directly to that location. You will be returned to the current + search results after exiting this new menu. + ---------------------------------------------------------------------- User interface options for 'menuconfig' @@ -259,6 +277,10 @@ Searching in nconfig: F8 (SymSearch) searches the configuration symbols for the given string or regular expression (regex). + In the SymSearch, pressing the key in the (#) prefix will + jump directly to that location. You will be returned to the + current search results after exiting this new menu. + NCONFIG_MODE ------------ This mode shows all sub-menus in one large tree. diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst new file mode 100644 index 000000000000..b1d97fafddcf --- /dev/null +++ b/Documentation/kbuild/llvm.rst @@ -0,0 +1,222 @@ +.. _kbuild_llvm: + +============================== +Building Linux with Clang/LLVM +============================== + +This document covers how to build the Linux kernel with Clang and LLVM +utilities. + +About +----- + +The Linux kernel has always traditionally been compiled with GNU toolchains +such as GCC and binutils. Ongoing work has allowed for `Clang +<https://clang.llvm.org/>`_ and `LLVM <https://llvm.org/>`_ utilities to be +used as viable substitutes. Distributions such as `Android +<https://www.android.com/>`_, `ChromeOS +<https://www.chromium.org/chromium-os>`_, `OpenMandriva +<https://www.openmandriva.org/>`_, and `Chimera Linux +<https://chimera-linux.org/>`_ use Clang built kernels. Google's and Meta's +datacenter fleets also run kernels built with Clang. + +`LLVM is a collection of toolchain components implemented in terms of C++ +objects <https://www.aosabook.org/en/llvm.html>`_. Clang is a front-end to LLVM +that supports C and the GNU C extensions required by the kernel, and is +pronounced "klang," not "see-lang." + +Building with LLVM +------------------ + +Invoke ``make`` via:: + + make LLVM=1 + +to compile for the host target. For cross compiling:: + + make LLVM=1 ARCH=arm64 + +The LLVM= argument +------------------ + +LLVM has substitutes for GNU binutils utilities. They can be enabled +individually. The full list of supported make variables:: + + make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \ + OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf \ + HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar HOSTLD=ld.lld + +``LLVM=1`` expands to the above. + +If your LLVM tools are not available in your PATH, you can supply their +location using the LLVM variable with a trailing slash:: + + make LLVM=/path/to/llvm/ + +which will use ``/path/to/llvm/clang``, ``/path/to/llvm/ld.lld``, etc. The +following may also be used:: + + PATH=/path/to/llvm:$PATH make LLVM=1 + +If your LLVM tools have a version suffix and you want to test with that +explicit version rather than the unsuffixed executables like ``LLVM=1``, you +can pass the suffix using the ``LLVM`` variable:: + + make LLVM=-14 + +which will use ``clang-14``, ``ld.lld-14``, etc. + +To support combinations of out of tree paths with version suffixes, we +recommend:: + + PATH=/path/to/llvm/:$PATH make LLVM=-14 + +``LLVM=0`` is not the same as omitting ``LLVM`` altogether, it will behave like +``LLVM=1``. If you only wish to use certain LLVM utilities, use their +respective make variables. + +The same value used for ``LLVM=`` should be set for each invocation of ``make`` +if configuring and building via distinct commands. ``LLVM=`` should also be set +as an environment variable when running scripts that will eventually run +``make``. + +Cross Compiling +--------------- + +A single Clang compiler binary (and corresponding LLVM utilities) will +typically contain all supported back ends, which can help simplify cross +compiling especially when ``LLVM=1`` is used. If you use only LLVM tools, +``CROSS_COMPILE`` or target-triple-prefixes become unnecessary. Example:: + + make LLVM=1 ARCH=arm64 + +As an example of mixing LLVM and GNU utilities, for a target like ``ARCH=s390`` +which does not yet have ``ld.lld`` or ``llvm-objcopy`` support, you could +invoke ``make`` via:: + + make LLVM=1 ARCH=s390 LD=s390x-linux-gnu-ld.bfd \ + OBJCOPY=s390x-linux-gnu-objcopy + +This example will invoke ``s390x-linux-gnu-ld.bfd`` as the linker and +``s390x-linux-gnu-objcopy``, so ensure those are reachable in your ``$PATH``. + +``CROSS_COMPILE`` is not used to prefix the Clang compiler binary (or +corresponding LLVM utilities) as is the case for GNU utilities when ``LLVM=1`` +is not set. + +The LLVM_IAS= argument +---------------------- + +Clang can assemble assembler code. You can pass ``LLVM_IAS=0`` to disable this +behavior and have Clang invoke the corresponding non-integrated assembler +instead. Example:: + + make LLVM=1 LLVM_IAS=0 + +``CROSS_COMPILE`` is necessary when cross compiling and ``LLVM_IAS=0`` +is used in order to set ``--prefix=`` for the compiler to find the +corresponding non-integrated assembler (typically, you don't want to use the +system assembler when targeting another architecture). Example:: + + make LLVM=1 ARCH=arm LLVM_IAS=0 CROSS_COMPILE=arm-linux-gnueabi- + + +Ccache +------ + +``ccache`` can be used with ``clang`` to improve subsequent builds, (though +KBUILD_BUILD_TIMESTAMP_ should be set to a deterministic value between builds +in order to avoid 100% cache misses, see Reproducible_builds_ for more info): + + KBUILD_BUILD_TIMESTAMP='' make LLVM=1 CC="ccache clang" + +.. _KBUILD_BUILD_TIMESTAMP: kbuild.html#kbuild-build-timestamp +.. _Reproducible_builds: reproducible-builds.html#timestamps + +Supported Architectures +----------------------- + +LLVM does not target all of the architectures that Linux supports and +just because a target is supported in LLVM does not mean that the kernel +will build or work without any issues. Below is a general summary of +architectures that currently work with ``CC=clang`` or ``LLVM=1``. Level +of support corresponds to "S" values in the MAINTAINERS files. If an +architecture is not present, it either means that LLVM does not target +it or there are known issues. Using the latest stable version of LLVM or +even the development tree will generally yield the best results. +An architecture's ``defconfig`` is generally expected to work well, +certain configurations may have problems that have not been uncovered +yet. Bug reports are always welcome at the issue tracker below! + +.. list-table:: + :widths: 10 10 10 + :header-rows: 1 + + * - Architecture + - Level of support + - ``make`` command + * - arm + - Supported + - ``LLVM=1`` + * - arm64 + - Supported + - ``LLVM=1`` + * - hexagon + - Maintained + - ``LLVM=1`` + * - loongarch + - Maintained + - ``LLVM=1`` + * - mips + - Maintained + - ``LLVM=1`` + * - powerpc + - Maintained + - ``LLVM=1`` + * - riscv + - Supported + - ``LLVM=1`` + * - s390 + - Maintained + - ``CC=clang`` + * - um (User Mode) + - Maintained + - ``LLVM=1`` + * - x86 + - Supported + - ``LLVM=1`` + +Getting Help +------------ + +- `Website <https://clangbuiltlinux.github.io/>`_ +- `Mailing List <https://lore.kernel.org/llvm/>`_: <llvm@lists.linux.dev> +- `Old Mailing List Archives <https://groups.google.com/g/clang-built-linux>`_ +- `Issue Tracker <https://github.com/ClangBuiltLinux/linux/issues>`_ +- IRC: #clangbuiltlinux on irc.libera.chat +- `Telegram <https://t.me/ClangBuiltLinux>`_: @ClangBuiltLinux +- `Wiki <https://github.com/ClangBuiltLinux/linux/wiki>`_ +- `Beginner Bugs <https://github.com/ClangBuiltLinux/linux/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22>`_ + +.. _getting_llvm: + +Getting LLVM +------------- + +We provide prebuilt stable versions of LLVM on `kernel.org +<https://kernel.org/pub/tools/llvm/>`_. These have been optimized with profile +data for building Linux kernels, which should improve kernel build times +relative to other distributions of LLVM. + +Below are links that may be useful for building LLVM from source or procuring +it through a distribution's package manager. + +- https://releases.llvm.org/download.html +- https://github.com/llvm/llvm-project +- https://llvm.org/docs/GettingStarted.html +- https://llvm.org/docs/CMake.html +- https://apt.llvm.org/ +- https://www.archlinux.org/packages/extra/x86_64/llvm/ +- https://github.com/ClangBuiltLinux/tc-build +- https://github.com/ClangBuiltLinux/linux/wiki/Building-Clang-from-source +- https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/ diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst index b9b50553bfc5..ad118b7a1806 100644 --- a/Documentation/kbuild/makefiles.rst +++ b/Documentation/kbuild/makefiles.rst @@ -4,68 +4,16 @@ Linux Kernel Makefiles This document describes the Linux kernel Makefiles. -.. Table of Contents - - === 1 Overview - === 2 Who does what - === 3 The kbuild files - --- 3.1 Goal definitions - --- 3.2 Built-in object goals - obj-y - --- 3.3 Loadable module goals - obj-m - --- 3.4 Objects which export symbols - --- 3.5 Library file goals - lib-y - --- 3.6 Descending down in directories - --- 3.7 Compilation flags - --- 3.8 Command line dependency - --- 3.9 Dependency tracking - --- 3.10 Special Rules - --- 3.11 $(CC) support functions - --- 3.12 $(LD) support functions - - === 4 Host Program support - --- 4.1 Simple Host Program - --- 4.2 Composite Host Programs - --- 4.3 Using C++ for host programs - --- 4.4 Controlling compiler options for host programs - --- 4.5 When host programs are actually built - --- 4.6 Using hostprogs-$(CONFIG_FOO) - - === 5 Kbuild clean infrastructure - - === 6 Architecture Makefiles - --- 6.1 Set variables to tweak the build to the architecture - --- 6.2 Add prerequisites to archheaders: - --- 6.3 Add prerequisites to archprepare: - --- 6.4 List directories to visit when descending - --- 6.5 Architecture-specific boot images - --- 6.6 Building non-kbuild targets - --- 6.7 Commands useful for building a boot image - --- 6.8 Custom kbuild commands - --- 6.9 Preprocessing linker scripts - --- 6.10 Generic header files - --- 6.11 Post-link pass - - === 7 Kbuild syntax for exported headers - --- 7.1 no-export-headers - --- 7.2 generic-y - --- 7.3 generated-y - --- 7.4 mandatory-y - - === 8 Kbuild Variables - === 9 Makefile language - === 10 Credits - === 11 TODO - -1 Overview -========== +Overview +======== The Makefiles have five parts:: - Makefile the top Makefile. - .config the kernel configuration file. - arch/$(ARCH)/Makefile the arch Makefile. - scripts/Makefile.* common rules etc. for all kbuild Makefiles. - kbuild Makefiles there are about 500 of these. + Makefile the top Makefile. + .config the kernel configuration file. + arch/$(SRCARCH)/Makefile the arch Makefile. + scripts/Makefile.* common rules etc. for all kbuild Makefiles. + kbuild Makefiles exist in every subdirectory The top Makefile reads the .config file, which comes from the kernel configuration process. @@ -74,9 +22,10 @@ The top Makefile is responsible for building two major products: vmlinux (the resident kernel image) and modules (any module files). It builds these goals by recursively descending into the subdirectories of the kernel source tree. + The list of subdirectories which are visited depends upon the kernel configuration. The top Makefile textually includes an arch Makefile -with the name arch/$(ARCH)/Makefile. The arch Makefile supplies +with the name arch/$(SRCARCH)/Makefile. The arch Makefile supplies architecture-specific information to the top Makefile. Each subdirectory has a kbuild Makefile which carries out the commands @@ -87,14 +36,13 @@ any built-in or modular targets. scripts/Makefile.* contains all the definitions/rules etc. that are used to build the kernel based on the kbuild makefiles. - -2 Who does what -=============== +Who does what +============= People have four different relationships with the kernel Makefiles. *Users* are people who build kernels. These people type commands such as -"make menuconfig" or "make". They usually do not read or edit +``make menuconfig`` or ``make``. They usually do not read or edit any kernel Makefiles (or any other source files). *Normal developers* are people who work on features such as device @@ -105,7 +53,7 @@ knowledge about the kernel Makefiles, plus detailed knowledge about the public interface for kbuild. *Arch developers* are people who work on an entire architecture, such -as sparc or ia64. Arch developers need to know about the arch Makefile +as sparc or x86. Arch developers need to know about the arch Makefile as well as kbuild Makefiles. *Kbuild developers* are people who work on the kernel build system itself. @@ -114,1208 +62,1433 @@ These people need to know about all aspects of the kernel Makefiles. This document is aimed towards normal developers and arch developers. -3 The kbuild files -================== +The kbuild files +================ Most Makefiles within the kernel are kbuild Makefiles that use the kbuild infrastructure. This chapter introduces the syntax used in the kbuild makefiles. -The preferred name for the kbuild files are 'Makefile' but 'Kbuild' can -be used and if both a 'Makefile' and a 'Kbuild' file exists, then the 'Kbuild' + +The preferred name for the kbuild files are ``Makefile`` but ``Kbuild`` can +be used and if both a ``Makefile`` and a ``Kbuild`` file exists, then the ``Kbuild`` file will be used. -Section 3.1 "Goal definitions" is a quick intro, further chapters provide +Section `Goal definitions`_ is a quick intro; further chapters provide more details, with real examples. -3.1 Goal definitions --------------------- +Goal definitions +---------------- - Goal definitions are the main part (heart) of the kbuild Makefile. - These lines define the files to be built, any special compilation - options, and any subdirectories to be entered recursively. +Goal definitions are the main part (heart) of the kbuild Makefile. +These lines define the files to be built, any special compilation +options, and any subdirectories to be entered recursively. - The most simple kbuild makefile contains one line: +The most simple kbuild makefile contains one line: - Example:: +Example:: - obj-y += foo.o + obj-y += foo.o - This tells kbuild that there is one object in that directory, named - foo.o. foo.o will be built from foo.c or foo.S. +This tells kbuild that there is one object in that directory, named +foo.o. foo.o will be built from foo.c or foo.S. - If foo.o shall be built as a module, the variable obj-m is used. - Therefore the following pattern is often used: +If foo.o shall be built as a module, the variable obj-m is used. +Therefore the following pattern is often used: - Example:: +Example:: - obj-$(CONFIG_FOO) += foo.o + obj-$(CONFIG_FOO) += foo.o - $(CONFIG_FOO) evaluates to either y (for built-in) or m (for module). - If CONFIG_FOO is neither y nor m, then the file will not be compiled - nor linked. +$(CONFIG_FOO) evaluates to either y (for built-in) or m (for module). +If CONFIG_FOO is neither y nor m, then the file will not be compiled +nor linked. -3.2 Built-in object goals - obj-y ---------------------------------- +Built-in object goals - obj-y +----------------------------- - The kbuild Makefile specifies object files for vmlinux - in the $(obj-y) lists. These lists depend on the kernel - configuration. +The kbuild Makefile specifies object files for vmlinux +in the $(obj-y) lists. These lists depend on the kernel +configuration. - Kbuild compiles all the $(obj-y) files. It then calls - "$(AR) rcSTP" to merge these files into one built-in.a file. - This is a thin archive without a symbol table. It will be later - linked into vmlinux by scripts/link-vmlinux.sh +Kbuild compiles all the $(obj-y) files. It then calls +``$(AR) rcSTP`` to merge these files into one built-in.a file. +This is a thin archive without a symbol table. It will be later +linked into vmlinux by scripts/link-vmlinux.sh - The order of files in $(obj-y) is significant. Duplicates in - the lists are allowed: the first instance will be linked into - built-in.a and succeeding instances will be ignored. +The order of files in $(obj-y) is significant. Duplicates in +the lists are allowed: the first instance will be linked into +built-in.a and succeeding instances will be ignored. - Link order is significant, because certain functions - (module_init() / __initcall) will be called during boot in the - order they appear. So keep in mind that changing the link - order may e.g. change the order in which your SCSI - controllers are detected, and thus your disks are renumbered. +Link order is significant, because certain functions +(module_init() / __initcall) will be called during boot in the +order they appear. So keep in mind that changing the link +order may e.g. change the order in which your SCSI +controllers are detected, and thus your disks are renumbered. - Example:: +Example:: - #drivers/isdn/i4l/Makefile - # Makefile for the kernel ISDN subsystem and device drivers. - # Each configuration option enables a list of files. - obj-$(CONFIG_ISDN_I4L) += isdn.o - obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o + #drivers/isdn/i4l/Makefile + # Makefile for the kernel ISDN subsystem and device drivers. + # Each configuration option enables a list of files. + obj-$(CONFIG_ISDN_I4L) += isdn.o + obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o -3.3 Loadable module goals - obj-m ---------------------------------- +Loadable module goals - obj-m +----------------------------- - $(obj-m) specifies object files which are built as loadable - kernel modules. +$(obj-m) specifies object files which are built as loadable +kernel modules. - A module may be built from one source file or several source - files. In the case of one source file, the kbuild makefile - simply adds the file to $(obj-m). +A module may be built from one source file or several source +files. In the case of one source file, the kbuild makefile +simply adds the file to $(obj-m). - Example:: +Example:: - #drivers/isdn/i4l/Makefile - obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o + #drivers/isdn/i4l/Makefile + obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o - Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm' +Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to "m" - If a kernel module is built from several source files, you specify - that you want to build a module in the same way as above; however, - kbuild needs to know which object files you want to build your - module from, so you have to tell it by setting a $(<module_name>-y) - variable. +If a kernel module is built from several source files, you specify +that you want to build a module in the same way as above; however, +kbuild needs to know which object files you want to build your +module from, so you have to tell it by setting a $(<module_name>-y) +variable. - Example:: +Example:: - #drivers/isdn/i4l/Makefile - obj-$(CONFIG_ISDN_I4L) += isdn.o - isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o + #drivers/isdn/i4l/Makefile + obj-$(CONFIG_ISDN_I4L) += isdn.o + isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o - In this example, the module name will be isdn.o. Kbuild will - compile the objects listed in $(isdn-y) and then run - "$(LD) -r" on the list of these files to generate isdn.o. +In this example, the module name will be isdn.o. Kbuild will +compile the objects listed in $(isdn-y) and then run +``$(LD) -r`` on the list of these files to generate isdn.o. - Due to kbuild recognizing $(<module_name>-y) for composite objects, - you can use the value of a `CONFIG_` symbol to optionally include an - object file as part of a composite object. +Due to kbuild recognizing $(<module_name>-y) for composite objects, +you can use the value of a ``CONFIG_`` symbol to optionally include an +object file as part of a composite object. - Example:: +Example:: - #fs/ext2/Makefile - obj-$(CONFIG_EXT2_FS) += ext2.o - ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \ - namei.o super.o symlink.o - ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \ - xattr_trusted.o + #fs/ext2/Makefile + obj-$(CONFIG_EXT2_FS) += ext2.o + ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \ + namei.o super.o symlink.o + ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \ + xattr_trusted.o - In this example, xattr.o, xattr_user.o and xattr_trusted.o are only - part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR) - evaluates to 'y'. +In this example, xattr.o, xattr_user.o and xattr_trusted.o are only +part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR) +evaluates to "y". - Note: Of course, when you are building objects into the kernel, - the syntax above will also work. So, if you have CONFIG_EXT2_FS=y, - kbuild will build an ext2.o file for you out of the individual - parts and then link this into built-in.a, as you would expect. +Note: Of course, when you are building objects into the kernel, +the syntax above will also work. So, if you have CONFIG_EXT2_FS=y, +kbuild will build an ext2.o file for you out of the individual +parts and then link this into built-in.a, as you would expect. -3.4 Objects which export symbols --------------------------------- +Library file goals - lib-y +-------------------------- + +Objects listed with obj-* are used for modules, or +combined in a built-in.a for that specific directory. +There is also the possibility to list objects that will +be included in a library, lib.a. +All objects listed with lib-y are combined in a single +library for that directory. +Objects that are listed in obj-y and additionally listed in +lib-y will not be included in the library, since they will +be accessible anyway. +For consistency, objects listed in lib-m will be included in lib.a. + +Note that the same kbuild makefile may list files to be built-in +and to be part of a library. Therefore the same directory +may contain both a built-in.a and a lib.a file. + +Example:: + + #arch/x86/lib/Makefile + lib-y := delay.o + +This will create a library lib.a based on delay.o. For kbuild to +actually recognize that there is a lib.a being built, the directory +shall be listed in libs-y. - No special notation is required in the makefiles for - modules exporting symbols. +See also `List directories to visit when descending`_. -3.5 Library file goals - lib-y +Use of lib-y is normally restricted to ``lib/`` and ``arch/*/lib``. + +Descending down in directories ------------------------------ - Objects listed with obj-* are used for modules, or - combined in a built-in.a for that specific directory. - There is also the possibility to list objects that will - be included in a library, lib.a. - All objects listed with lib-y are combined in a single - library for that directory. - Objects that are listed in obj-y and additionally listed in - lib-y will not be included in the library, since they will - be accessible anyway. - For consistency, objects listed in lib-m will be included in lib.a. +A Makefile is only responsible for building objects in its own +directory. Files in subdirectories should be taken care of by +Makefiles in these subdirs. The build system will automatically +invoke make recursively in subdirectories, provided you let it know of +them. + +To do so, obj-y and obj-m are used. +ext2 lives in a separate directory, and the Makefile present in fs/ +tells kbuild to descend down using the following assignment. + +Example:: + + #fs/Makefile + obj-$(CONFIG_EXT2_FS) += ext2/ + +If CONFIG_EXT2_FS is set to either "y" (built-in) or "m" (modular) +the corresponding obj- variable will be set, and kbuild will descend +down in the ext2 directory. + +Kbuild uses this information not only to decide that it needs to visit +the directory, but also to decide whether or not to link objects from +the directory into vmlinux. + +When Kbuild descends into the directory with "y", all built-in objects +from that directory are combined into the built-in.a, which will be +eventually linked into vmlinux. + +When Kbuild descends into the directory with "m", in contrast, nothing +from that directory will be linked into vmlinux. If the Makefile in +that directory specifies obj-y, those objects will be left orphan. +It is very likely a bug of the Makefile or of dependencies in Kconfig. + +Kbuild also supports dedicated syntax, subdir-y and subdir-m, for +descending into subdirectories. It is a good fit when you know they +do not contain kernel-space objects at all. A typical usage is to let +Kbuild descend into subdirectories to build tools. + +Examples:: + + # scripts/Makefile + subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins + subdir-$(CONFIG_MODVERSIONS) += genksyms + subdir-$(CONFIG_SECURITY_SELINUX) += selinux + +Unlike obj-y/m, subdir-y/m does not need the trailing slash since this +syntax is always used for directories. + +It is good practice to use a ``CONFIG_`` variable when assigning directory +names. This allows kbuild to totally skip the directory if the +corresponding ``CONFIG_`` option is neither "y" nor "m". + +Non-builtin vmlinux targets - extra-y +------------------------------------- + +extra-y specifies targets which are needed for building vmlinux, +but not combined into built-in.a. + +Examples are: + +1) vmlinux linker script + + The linker script for vmlinux is located at + arch/$(SRCARCH)/kernel/vmlinux.lds + +Example:: + + # arch/x86/kernel/Makefile + extra-y += vmlinux.lds + +$(extra-y) should only contain targets needed for vmlinux. + +Kbuild skips extra-y when vmlinux is apparently not a final goal. +(e.g. ``make modules``, or building external modules) + +If you intend to build targets unconditionally, always-y (explained +in the next section) is the correct syntax to use. + +Always built goals - always-y +----------------------------- + +always-y specifies targets which are literally always built when +Kbuild visits the Makefile. + +Example:: + + # ./Kbuild + offsets-file := include/generated/asm-offsets.h + always-y += $(offsets-file) + +Compilation flags +----------------- + +ccflags-y, asflags-y and ldflags-y + These three flags apply only to the kbuild makefile in which they + are assigned. They are used for all the normal cc, as and ld + invocations happening during a recursive build. + Note: Flags with the same behaviour were previously named: + EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS. + They are still supported but their usage is deprecated. + + ccflags-y specifies options for compiling with $(CC). + + Example:: + + # drivers/acpi/acpica/Makefile + ccflags-y := -Os -D_LINUX -DBUILDING_ACPICA + ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT + + This variable is necessary because the top Makefile owns the + variable $(KBUILD_CFLAGS) and uses it for compilation flags for the + entire tree. + + asflags-y specifies assembler options. + + Example:: + + #arch/sparc/kernel/Makefile + asflags-y := -ansi + + ldflags-y specifies options for linking with $(LD). - Note that the same kbuild makefile may list files to be built-in - and to be part of a library. Therefore the same directory - may contain both a built-in.a and a lib.a file. + Example:: - Example:: + #arch/cris/boot/compressed/Makefile + ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds - #arch/x86/lib/Makefile - lib-y := delay.o +subdir-ccflags-y, subdir-asflags-y + The two flags listed above are similar to ccflags-y and asflags-y. + The difference is that the subdir- variants have effect for the kbuild + file where they are present and all subdirectories. + Options specified using subdir-* are added to the commandline before + the options specified using the non-subdir variants. - This will create a library lib.a based on delay.o. For kbuild to - actually recognize that there is a lib.a being built, the directory - shall be listed in libs-y. + Example:: - See also "6.4 List directories to visit when descending". + subdir-ccflags-y := -Werror - Use of lib-y is normally restricted to `lib/` and `arch/*/lib`. +ccflags-remove-y, asflags-remove-y + These flags are used to remove particular flags for the compiler, + assembler invocations. -3.6 Descending down in directories ----------------------------------- + Example:: - A Makefile is only responsible for building objects in its own - directory. Files in subdirectories should be taken care of by - Makefiles in these subdirs. The build system will automatically - invoke make recursively in subdirectories, provided you let it know of - them. + ccflags-remove-$(CONFIG_MCOUNT) += -pg - To do so, obj-y and obj-m are used. - ext2 lives in a separate directory, and the Makefile present in fs/ - tells kbuild to descend down using the following assignment. +CFLAGS_$@, AFLAGS_$@ + CFLAGS_$@ and AFLAGS_$@ only apply to commands in current + kbuild makefile. - Example:: + $(CFLAGS_$@) specifies per-file options for $(CC). The $@ + part has a literal value which specifies the file that it is for. - #fs/Makefile - obj-$(CONFIG_EXT2_FS) += ext2/ + CFLAGS_$@ has the higher priority than ccflags-remove-y; CFLAGS_$@ + can re-add compiler flags that were removed by ccflags-remove-y. - If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular) - the corresponding obj- variable will be set, and kbuild will descend - down in the ext2 directory. - Kbuild only uses this information to decide that it needs to visit - the directory, it is the Makefile in the subdirectory that - specifies what is modular and what is built-in. + Example:: - It is good practice to use a `CONFIG_` variable when assigning directory - names. This allows kbuild to totally skip the directory if the - corresponding `CONFIG_` option is neither 'y' nor 'm'. + # drivers/scsi/Makefile + CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF -3.7 Compilation flags ---------------------- + This line specify compilation flags for aha152x.o. - ccflags-y, asflags-y and ldflags-y - These three flags apply only to the kbuild makefile in which they - are assigned. They are used for all the normal cc, as and ld - invocations happening during a recursive build. - Note: Flags with the same behaviour were previously named: - EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS. - They are still supported but their usage is deprecated. + $(AFLAGS_$@) is a similar feature for source files in assembly + languages. - ccflags-y specifies options for compiling with $(CC). + AFLAGS_$@ has the higher priority than asflags-remove-y; AFLAGS_$@ + can re-add assembler flags that were removed by asflags-remove-y. - Example:: + Example:: - # drivers/acpi/acpica/Makefile - ccflags-y := -Os -D_LINUX -DBUILDING_ACPICA - ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT + # arch/arm/kernel/Makefile + AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) + AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312 + AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt - This variable is necessary because the top Makefile owns the - variable $(KBUILD_CFLAGS) and uses it for compilation flags for the - entire tree. +Dependency tracking +------------------- + +Kbuild tracks dependencies on the following: + +1) All prerequisite files (both ``*.c`` and ``*.h``) +2) ``CONFIG_`` options used in all prerequisite files +3) Command-line used to compile target + +Thus, if you change an option to $(CC) all affected files will +be re-compiled. + +Custom Rules +------------ + +Custom rules are used when the kbuild infrastructure does +not provide the required support. A typical example is +header files generated during the build process. +Another example are the architecture-specific Makefiles which +need custom rules to prepare boot images etc. + +Custom rules are written as normal Make rules. +Kbuild is not executing in the directory where the Makefile is +located, so all custom rules shall use a relative +path to prerequisite files and target files. + +Two variables are used when defining custom rules: + +$(src) + $(src) is a relative path which points to the directory + where the Makefile is located. Always use $(src) when + referring to files located in the src tree. + +$(obj) + $(obj) is a relative path which points to the directory + where the target is saved. Always use $(obj) when + referring to generated files. + + Example:: + + #drivers/scsi/Makefile + $(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl + $(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl + + This is a custom rule, following the normal syntax + required by make. - asflags-y specifies assembler options. + The target file depends on two prerequisite files. References + to the target file are prefixed with $(obj), references + to prerequisites are referenced with $(src) (because they are not + generated files). - Example:: +$(kecho) + echoing information to user in a rule is often a good practice + but when execution ``make -s`` one does not expect to see any output + except for warnings/errors. + To support this kbuild defines $(kecho) which will echo out the + text following $(kecho) to stdout except if ``make -s`` is used. - #arch/sparc/kernel/Makefile - asflags-y := -ansi + Example:: - ldflags-y specifies options for linking with $(LD). + # arch/arm/Makefile + $(BOOT_TARGETS): vmlinux + $(Q)$(MAKE) $(build)=$(boot) MACHINE=$(MACHINE) $(boot)/$@ + @$(kecho) ' Kernel: $(boot)/$@ is ready' - Example:: + When kbuild is executing with KBUILD_VERBOSE unset, then only a shorthand + of a command is normally displayed. + To enable this behaviour for custom commands kbuild requires + two variables to be set:: - #arch/cris/boot/compressed/Makefile - ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds + quiet_cmd_<command> - what shall be echoed + cmd_<command> - the command to execute - subdir-ccflags-y, subdir-asflags-y - The two flags listed above are similar to ccflags-y and asflags-y. - The difference is that the subdir- variants have effect for the kbuild - file where they are present and all subdirectories. - Options specified using subdir-* are added to the commandline before - the options specified using the non-subdir variants. + Example:: - Example:: + # lib/Makefile + quiet_cmd_crc32 = GEN $@ + cmd_crc32 = $< > $@ - subdir-ccflags-y := -Werror + $(obj)/crc32table.h: $(obj)/gen_crc32table + $(call cmd,crc32) - CFLAGS_$@, AFLAGS_$@ - CFLAGS_$@ and AFLAGS_$@ only apply to commands in current - kbuild makefile. + When updating the $(obj)/crc32table.h target, the line:: - $(CFLAGS_$@) specifies per-file options for $(CC). The $@ - part has a literal value which specifies the file that it is for. + GEN lib/crc32table.h - Example:: + will be displayed with ``make KBUILD_VERBOSE=``. - # drivers/scsi/Makefile - CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF - CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \ - -DGDTH_STATISTICS +Command change detection +------------------------ - These two lines specify compilation flags for aha152x.o and gdth.o. +When the rule is evaluated, timestamps are compared between the target +and its prerequisite files. GNU Make updates the target when any of the +prerequisites is newer than that. - $(AFLAGS_$@) is a similar feature for source files in assembly - languages. +The target should be rebuilt also when the command line has changed +since the last invocation. This is not supported by Make itself, so +Kbuild achieves this by a kind of meta-programming. - Example:: +if_changed is the macro used for this purpose, in the following form:: - # arch/arm/kernel/Makefile - AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) - AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312 - AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt + quiet_cmd_<command> = ... + cmd_<command> = ... + <target>: <source(s)> FORCE + $(call if_changed,<command>) -3.9 Dependency tracking +Any target that utilizes if_changed must be listed in $(targets), +otherwise the command line check will fail, and the target will +always be built. + +If the target is already listed in the recognized syntax such as +obj-y/m, lib-y/m, extra-y/m, always-y/m, hostprogs, userprogs, Kbuild +automatically adds it to $(targets). Otherwise, the target must be +explicitly added to $(targets). + +Assignments to $(targets) are without $(obj)/ prefix. if_changed may be +used in conjunction with custom rules as defined in `Custom Rules`_. + +Note: It is a typical mistake to forget the FORCE prerequisite. +Another common pitfall is that whitespace is sometimes significant; for +instance, the below will fail (note the extra space after the comma):: + + target: source(s) FORCE + +**WRONG!** $(call if_changed, objcopy) + +Note: + if_changed should not be used more than once per target. + It stores the executed command in a corresponding .cmd + file and multiple calls would result in overwrites and + unwanted results when the target is up to date and only the + tests on changed commands trigger execution of commands. + +$(CC) support functions ----------------------- - Kbuild tracks dependencies on the following: +The kernel may be built with several different versions of +$(CC), each supporting a unique set of features and options. +kbuild provides basic support to check for valid options for $(CC). +$(CC) is usually the gcc compiler, but other alternatives are +available. - 1) All prerequisite files (both `*.c` and `*.h`) - 2) `CONFIG_` options used in all prerequisite files - 3) Command-line used to compile target +as-option + as-option is used to check if $(CC) -- when used to compile + assembler (``*.S``) files -- supports the given option. An optional + second option may be specified if the first option is not supported. - Thus, if you change an option to $(CC) all affected files will - be re-compiled. + Example:: -3.10 Special Rules ------------------- + #arch/sh/Makefile + cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),) - Special rules are used when the kbuild infrastructure does - not provide the required support. A typical example is - header files generated during the build process. - Another example are the architecture-specific Makefiles which - need special rules to prepare boot images etc. + In the above example, cflags-y will be assigned the option + -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC). + The second argument is optional, and if supplied will be used + if first argument is not supported. - Special rules are written as normal Make rules. - Kbuild is not executing in the directory where the Makefile is - located, so all special rules shall provide a relative - path to prerequisite files and target files. +as-instr + as-instr checks if the assembler reports a specific instruction + and then outputs either option1 or option2 + C escapes are supported in the test instruction + Note: as-instr-option uses KBUILD_AFLAGS for assembler options - Two variables are used when defining special rules: +cc-option + cc-option is used to check if $(CC) supports a given option, and if + not supported to use an optional second option. - $(src) - $(src) is a relative path which points to the directory - where the Makefile is located. Always use $(src) when - referring to files located in the src tree. + Example:: - $(obj) - $(obj) is a relative path which points to the directory - where the target is saved. Always use $(obj) when - referring to generated files. + #arch/x86/Makefile + cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) - Example:: + In the above example, cflags-y will be assigned the option + -march=pentium-mmx if supported by $(CC), otherwise -march=i586. + The second argument to cc-option is optional, and if omitted, + cflags-y will be assigned no value if first option is not supported. + Note: cc-option uses KBUILD_CFLAGS for $(CC) options - #drivers/scsi/Makefile - $(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl - $(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl +cc-option-yn + cc-option-yn is used to check if gcc supports a given option + and return "y" if supported, otherwise "n". - This is a special rule, following the normal syntax - required by make. + Example:: - The target file depends on two prerequisite files. References - to the target file are prefixed with $(obj), references - to prerequisites are referenced with $(src) (because they are not - generated files). + #arch/ppc/Makefile + biarch := $(call cc-option-yn, -m32) + aflags-$(biarch) += -a32 + cflags-$(biarch) += -m32 - $(kecho) - echoing information to user in a rule is often a good practice - but when execution "make -s" one does not expect to see any output - except for warnings/errors. - To support this kbuild defines $(kecho) which will echo out the - text following $(kecho) to stdout except if "make -s" is used. + In the above example, $(biarch) is set to y if $(CC) supports the -m32 + option. When $(biarch) equals "y", the expanded variables $(aflags-y) + and $(cflags-y) will be assigned the values -a32 and -m32, + respectively. - Example:: + Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options - #arch/blackfin/boot/Makefile - $(obj)/vmImage: $(obj)/vmlinux.gz - $(call if_changed,uimage) - @$(kecho) 'Kernel: $@ is ready' +cc-disable-warning + cc-disable-warning checks if gcc supports a given warning and returns + the commandline switch to disable it. This special function is needed, + because gcc 4.4 and later accept any unknown -Wno-* option and only + warn about it if there is another warning in the source file. + Example:: -3.11 $(CC) support functions ----------------------------- + KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) - The kernel may be built with several different versions of - $(CC), each supporting a unique set of features and options. - kbuild provides basic support to check for valid options for $(CC). - $(CC) is usually the gcc compiler, but other alternatives are - available. - - as-option - as-option is used to check if $(CC) -- when used to compile - assembler (`*.S`) files -- supports the given option. An optional - second option may be specified if the first option is not supported. - - Example:: - - #arch/sh/Makefile - cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),) - - In the above example, cflags-y will be assigned the option - -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC). - The second argument is optional, and if supplied will be used - if first argument is not supported. - - as-instr - as-instr checks if the assembler reports a specific instruction - and then outputs either option1 or option2 - C escapes are supported in the test instruction - Note: as-instr-option uses KBUILD_AFLAGS for assembler options - - cc-option - cc-option is used to check if $(CC) supports a given option, and if - not supported to use an optional second option. - - Example:: - - #arch/x86/Makefile - cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) - - In the above example, cflags-y will be assigned the option - -march=pentium-mmx if supported by $(CC), otherwise -march=i586. - The second argument to cc-option is optional, and if omitted, - cflags-y will be assigned no value if first option is not supported. - Note: cc-option uses KBUILD_CFLAGS for $(CC) options - - cc-option-yn - cc-option-yn is used to check if gcc supports a given option - and return 'y' if supported, otherwise 'n'. - - Example:: - - #arch/ppc/Makefile - biarch := $(call cc-option-yn, -m32) - aflags-$(biarch) += -a32 - cflags-$(biarch) += -m32 - - In the above example, $(biarch) is set to y if $(CC) supports the -m32 - option. When $(biarch) equals 'y', the expanded variables $(aflags-y) - and $(cflags-y) will be assigned the values -a32 and -m32, - respectively. - Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options - - cc-disable-warning - cc-disable-warning checks if gcc supports a given warning and returns - the commandline switch to disable it. This special function is needed, - because gcc 4.4 and later accept any unknown -Wno-* option and only - warn about it if there is another warning in the source file. - - Example:: - - KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) - - In the above example, -Wno-unused-but-set-variable will be added to - KBUILD_CFLAGS only if gcc really accepts it. - - cc-ifversion - cc-ifversion tests the version of $(CC) and equals the fourth parameter - if version expression is true, or the fifth (if given) if the version - expression is false. - - Example:: - - #fs/reiserfs/Makefile - ccflags-y := $(call cc-ifversion, -lt, 0402, -O1) - - In this example, ccflags-y will be assigned the value -O1 if the - $(CC) version is less than 4.2. - cc-ifversion takes all the shell operators: - -eq, -ne, -lt, -le, -gt, and -ge - The third parameter may be a text as in this example, but it may also - be an expanded variable or a macro. - - cc-cross-prefix - cc-cross-prefix is used to check if there exists a $(CC) in path with - one of the listed prefixes. The first prefix where there exist a - prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found - then nothing is returned. - Additional prefixes are separated by a single space in the - call of cc-cross-prefix. - This functionality is useful for architecture Makefiles that try - to set CROSS_COMPILE to well-known values but may have several - values to select between. - It is recommended only to try to set CROSS_COMPILE if it is a cross - build (host arch is different from target arch). And if CROSS_COMPILE - is already set then leave it with the old value. - - Example:: - - #arch/m68k/Makefile - ifneq ($(SUBARCH),$(ARCH)) - ifeq ($(CROSS_COMPILE),) - CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-) - endif - endif - -3.12 $(LD) support functions ----------------------------- + In the above example, -Wno-unused-but-set-variable will be added to + KBUILD_CFLAGS only if gcc really accepts it. - ld-option - ld-option is used to check if $(LD) supports the supplied option. - ld-option takes two options as arguments. - The second argument is an optional option that can be used if the - first option is not supported by $(LD). +gcc-min-version + gcc-min-version tests if the value of $(CONFIG_GCC_VERSION) is greater than + or equal to the provided value and evaluates to y if so. - Example:: + Example:: - #Makefile - LDFLAGS_vmlinux += $(call ld-option, -X) + cflags-$(call gcc-min-version, 70100) := -foo + In this example, cflags-y will be assigned the value -foo if $(CC) is gcc and + $(CONFIG_GCC_VERSION) is >= 7.1. -4 Host Program support -====================== +clang-min-version + clang-min-version tests if the value of $(CONFIG_CLANG_VERSION) is greater + than or equal to the provided value and evaluates to y if so. + + Example:: + + cflags-$(call clang-min-version, 110000) := -foo + + In this example, cflags-y will be assigned the value -foo if $(CC) is clang + and $(CONFIG_CLANG_VERSION) is >= 11.0.0. + +cc-cross-prefix + cc-cross-prefix is used to check if there exists a $(CC) in path with + one of the listed prefixes. The first prefix where there exist a + prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found + then nothing is returned. + + Additional prefixes are separated by a single space in the + call of cc-cross-prefix. + + This functionality is useful for architecture Makefiles that try + to set CROSS_COMPILE to well-known values but may have several + values to select between. + + It is recommended only to try to set CROSS_COMPILE if it is a cross + build (host arch is different from target arch). And if CROSS_COMPILE + is already set then leave it with the old value. + + Example:: + + #arch/m68k/Makefile + ifneq ($(SUBARCH),$(ARCH)) + ifeq ($(CROSS_COMPILE),) + CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-) + endif + endif + +$(LD) support functions +----------------------- + +ld-option + ld-option is used to check if $(LD) supports the supplied option. + ld-option takes two options as arguments. + + The second argument is an optional option that can be used if the + first option is not supported by $(LD). + + Example:: + + #Makefile + LDFLAGS_vmlinux += $(call ld-option, -X) + +Script invocation +----------------- + +Make rules may invoke scripts to build the kernel. The rules shall +always provide the appropriate interpreter to execute the script. They +shall not rely on the execute bits being set, and shall not invoke the +script directly. For the convenience of manual script invocation, such +as invoking ./scripts/checkpatch.pl, it is recommended to set execute +bits on the scripts nonetheless. + +Kbuild provides variables $(CONFIG_SHELL), $(AWK), $(PERL), +and $(PYTHON3) to refer to interpreters for the respective +scripts. + +Example:: + + #Makefile + cmd_depmod = $(CONFIG_SHELL) $(srctree)/scripts/depmod.sh $(DEPMOD) \ + $(KERNELRELEASE) + +Host Program support +==================== Kbuild supports building executables on the host for use during the compilation stage. + Two steps are required in order to use a host executable. The first step is to tell kbuild that a host program exists. This is -done utilising the variable hostprogs-y. +done utilising the variable ``hostprogs``. The second step is to add an explicit dependency to the executable. This can be done in two ways. Either add the dependency in a rule, -or utilise the variable $(always). +or utilise the variable ``always-y``. Both possibilities are described in the following. -4.1 Simple Host Program +Simple Host Program +------------------- + +In some cases there is a need to compile and run a program on the +computer where the build is running. + +The following line tells kbuild that the program bin2hex shall be +built on the build host. + +Example:: + + hostprogs := bin2hex + +Kbuild assumes in the above example that bin2hex is made from a single +c-source file named bin2hex.c located in the same directory as +the Makefile. + +Composite Host Programs ----------------------- - In some cases there is a need to compile and run a program on the - computer where the build is running. - The following line tells kbuild that the program bin2hex shall be - built on the build host. +Host programs can be made up based on composite objects. +The syntax used to define composite objects for host programs is +similar to the syntax used for kernel objects. +$(<executable>-objs) lists all objects used to link the final +executable. + +Example:: - Example:: + #scripts/lxdialog/Makefile + hostprogs := lxdialog + lxdialog-objs := checklist.o lxdialog.o - hostprogs-y := bin2hex +Objects with extension .o are compiled from the corresponding .c +files. In the above example, checklist.c is compiled to checklist.o +and lxdialog.c is compiled to lxdialog.o. - Kbuild assumes in the above example that bin2hex is made from a single - c-source file named bin2hex.c located in the same directory as - the Makefile. +Finally, the two .o files are linked to the executable, lxdialog. +Note: The syntax <executable>-y is not permitted for host-programs. -4.2 Composite Host Programs +Using C++ for host programs --------------------------- - Host programs can be made up based on composite objects. - The syntax used to define composite objects for host programs is - similar to the syntax used for kernel objects. - $(<executable>-objs) lists all objects used to link the final - executable. +kbuild offers support for host programs written in C++. This was +introduced solely to support kconfig, and is not recommended +for general use. - Example:: +Example:: - #scripts/lxdialog/Makefile - hostprogs-y := lxdialog - lxdialog-objs := checklist.o lxdialog.o + #scripts/kconfig/Makefile + hostprogs := qconf + qconf-cxxobjs := qconf.o - Objects with extension .o are compiled from the corresponding .c - files. In the above example, checklist.c is compiled to checklist.o - and lxdialog.c is compiled to lxdialog.o. +In the example above the executable is composed of the C++ file +qconf.cc - identified by $(qconf-cxxobjs). - Finally, the two .o files are linked to the executable, lxdialog. - Note: The syntax <executable>-y is not permitted for host-programs. +If qconf is composed of a mixture of .c and .cc files, then an +additional line can be used to identify this. -4.3 Using C++ for host programs -------------------------------- +Example:: - kbuild offers support for host programs written in C++. This was - introduced solely to support kconfig, and is not recommended - for general use. + #scripts/kconfig/Makefile + hostprogs := qconf + qconf-cxxobjs := qconf.o + qconf-objs := check.o - Example:: +Using Rust for host programs +---------------------------- - #scripts/kconfig/Makefile - hostprogs-y := qconf - qconf-cxxobjs := qconf.o +Kbuild offers support for host programs written in Rust. However, +since a Rust toolchain is not mandatory for kernel compilation, +it may only be used in scenarios where Rust is required to be +available (e.g. when ``CONFIG_RUST`` is enabled). - In the example above the executable is composed of the C++ file - qconf.cc - identified by $(qconf-cxxobjs). +Example:: - If qconf is composed of a mixture of .c and .cc files, then an - additional line can be used to identify this. + hostprogs := target + target-rust := y - Example:: +Kbuild will compile ``target`` using ``target.rs`` as the crate root, +located in the same directory as the ``Makefile``. The crate may +consist of several source files (see ``samples/rust/hostprogs``). - #scripts/kconfig/Makefile - hostprogs-y := qconf - qconf-cxxobjs := qconf.o - qconf-objs := check.o +Controlling compiler options for host programs +---------------------------------------------- -4.4 Controlling compiler options for host programs --------------------------------------------------- +When compiling host programs, it is possible to set specific flags. +The programs will always be compiled utilising $(HOSTCC) passed +the options specified in $(KBUILD_HOSTCFLAGS). - When compiling host programs, it is possible to set specific flags. - The programs will always be compiled utilising $(HOSTCC) passed - the options specified in $(KBUILD_HOSTCFLAGS). - To set flags that will take effect for all host programs created - in that Makefile, use the variable HOST_EXTRACFLAGS. +To set flags that will take effect for all host programs created +in that Makefile, use the variable HOST_EXTRACFLAGS. - Example:: +Example:: - #scripts/lxdialog/Makefile - HOST_EXTRACFLAGS += -I/usr/include/ncurses + #scripts/lxdialog/Makefile + HOST_EXTRACFLAGS += -I/usr/include/ncurses - To set specific flags for a single file the following construction - is used: +To set specific flags for a single file the following construction +is used: - Example:: +Example:: - #arch/ppc64/boot/Makefile - HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE) + #arch/ppc64/boot/Makefile + HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE) - It is also possible to specify additional options to the linker. +It is also possible to specify additional options to the linker. - Example:: +Example:: - #scripts/kconfig/Makefile - HOSTLDLIBS_qconf := -L$(QTDIR)/lib + #scripts/kconfig/Makefile + HOSTLDLIBS_qconf := -L$(QTDIR)/lib - When linking qconf, it will be passed the extra option - "-L$(QTDIR)/lib". +When linking qconf, it will be passed the extra option +``-L$(QTDIR)/lib``. -4.5 When host programs are actually built ------------------------------------------ +When host programs are actually built +------------------------------------- - Kbuild will only build host-programs when they are referenced - as a prerequisite. - This is possible in two ways: +Kbuild will only build host-programs when they are referenced +as a prerequisite. - (1) List the prerequisite explicitly in a special rule. +This is possible in two ways: - Example:: +(1) List the prerequisite explicitly in a custom rule. - #drivers/pci/Makefile - hostprogs-y := gen-devlist - $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist - ( cd $(obj); ./gen-devlist ) < $< + Example:: - The target $(obj)/devlist.h will not be built before - $(obj)/gen-devlist is updated. Note that references to - the host programs in special rules must be prefixed with $(obj). + #drivers/pci/Makefile + hostprogs := gen-devlist + $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist + ( cd $(obj); ./gen-devlist ) < $< - (2) Use $(always) + The target $(obj)/devlist.h will not be built before + $(obj)/gen-devlist is updated. Note that references to + the host programs in custom rules must be prefixed with $(obj). - When there is no suitable special rule, and the host program - shall be built when a makefile is entered, the $(always) - variable shall be used. +(2) Use always-y - Example:: + When there is no suitable custom rule, and the host program + shall be built when a makefile is entered, the always-y + variable shall be used. - #scripts/lxdialog/Makefile - hostprogs-y := lxdialog - always := $(hostprogs-y) + Example:: - This will tell kbuild to build lxdialog even if not referenced in - any rule. + #scripts/lxdialog/Makefile + hostprogs := lxdialog + always-y := $(hostprogs) -4.6 Using hostprogs-$(CONFIG_FOO) ---------------------------------- + Kbuild provides the following shorthand for this:: + + hostprogs-always-y := lxdialog + + This will tell kbuild to build lxdialog even if not referenced in + any rule. + +Userspace Program support +========================= + +Just like host programs, Kbuild also supports building userspace executables +for the target architecture (i.e. the same architecture as you are building +the kernel for). + +The syntax is quite similar. The difference is to use ``userprogs`` instead of +``hostprogs``. + +Simple Userspace Program +------------------------ + +The following line tells kbuild that the program bpf-direct shall be +built for the target architecture. + +Example:: + + userprogs := bpf-direct + +Kbuild assumes in the above example that bpf-direct is made from a +single C source file named bpf-direct.c located in the same directory +as the Makefile. + +Composite Userspace Programs +---------------------------- + +Userspace programs can be made up based on composite objects. +The syntax used to define composite objects for userspace programs is +similar to the syntax used for kernel objects. +$(<executable>-objs) lists all objects used to link the final +executable. + +Example:: + + #samples/seccomp/Makefile + userprogs := bpf-fancy + bpf-fancy-objs := bpf-fancy.o bpf-helper.o + +Objects with extension .o are compiled from the corresponding .c +files. In the above example, bpf-fancy.c is compiled to bpf-fancy.o +and bpf-helper.c is compiled to bpf-helper.o. + +Finally, the two .o files are linked to the executable, bpf-fancy. +Note: The syntax <executable>-y is not permitted for userspace programs. + +Controlling compiler options for userspace programs +--------------------------------------------------- + +When compiling userspace programs, it is possible to set specific flags. +The programs will always be compiled utilising $(CC) passed +the options specified in $(KBUILD_USERCFLAGS). + +To set flags that will take effect for all userspace programs created +in that Makefile, use the variable userccflags. - A typical pattern in a Kbuild file looks like this: +Example:: - Example:: + # samples/seccomp/Makefile + userccflags += -I usr/include - #scripts/Makefile - hostprogs-$(CONFIG_KALLSYMS) += kallsyms +To set specific flags for a single file the following construction +is used: - Kbuild knows about both 'y' for built-in and 'm' for module. - So if a config symbol evaluates to 'm', kbuild will still build - the binary. In other words, Kbuild handles hostprogs-m exactly - like hostprogs-y. But only hostprogs-y is recommended to be used - when no CONFIG symbols are involved. +Example:: -5 Kbuild clean infrastructure -============================= + bpf-helper-userccflags += -I user/include -"make clean" deletes most generated files in the obj tree where the kernel +It is also possible to specify additional options to the linker. + +Example:: + + # net/bpfilter/Makefile + bpfilter_umh-userldflags += -static + +To specify libraries linked to a userspace program, you can use +``<executable>-userldlibs``. The ``userldlibs`` syntax specifies libraries +linked to all userspace programs created in the current Makefile. + +When linking bpfilter_umh, it will be passed the extra option -static. + +From command line, :ref:`USERCFLAGS and USERLDFLAGS <userkbuildflags>` will also be used. + +When userspace programs are actually built +------------------------------------------ + +Kbuild builds userspace programs only when told to do so. +There are two ways to do this. + +(1) Add it as the prerequisite of another file + + Example:: + + #net/bpfilter/Makefile + userprogs := bpfilter_umh + $(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh + + $(obj)/bpfilter_umh is built before $(obj)/bpfilter_umh_blob.o + +(2) Use always-y + + Example:: + + userprogs := binderfs_example + always-y := $(userprogs) + + Kbuild provides the following shorthand for this:: + + userprogs-always-y := binderfs_example + + This will tell Kbuild to build binderfs_example when it visits this + Makefile. + +Kbuild clean infrastructure +=========================== + +``make clean`` deletes most generated files in the obj tree where the kernel is compiled. This includes generated files such as host programs. -Kbuild knows targets listed in $(hostprogs-y), $(hostprogs-m), $(always), -$(extra-y) and $(targets). They are all deleted during "make clean". -Files matching the patterns "*.[oas]", "*.ko", plus some additional files -generated by kbuild are deleted all over the kernel src tree when -"make clean" is executed. +Kbuild knows targets listed in $(hostprogs), $(always-y), $(always-m), +$(always-), $(extra-y), $(extra-) and $(targets). They are all deleted +during ``make clean``. Files matching the patterns ``*.[oas]``, ``*.ko``, plus +some additional files generated by kbuild are deleted all over the kernel +source tree when ``make clean`` is executed. Additional files or directories can be specified in kbuild makefiles by use of $(clean-files). - Example:: +Example:: - #lib/Makefile - clean-files := crc32table.h + #lib/Makefile + clean-files := crc32table.h -When executing "make clean", the file "crc32table.h" will be deleted. +When executing ``make clean``, the file ``crc32table.h`` will be deleted. Kbuild will assume files to be in the same relative directory as the -Makefile, except if prefixed with $(objtree). +Makefile. To exclude certain files or directories from make clean, use the $(no-clean-files) variable. -Usually kbuild descends down in subdirectories due to "obj-* := dir/", +Usually kbuild descends down in subdirectories due to ``obj-* := dir/``, but in the architecture makefiles where the kbuild infrastructure is not sufficient this sometimes needs to be explicit. - Example:: +Example:: - #arch/x86/boot/Makefile - subdir- := compressed/ + #arch/x86/boot/Makefile + subdir- := compressed The above assignment instructs kbuild to descend down in the -directory compressed/ when "make clean" is executed. +directory compressed/ when ``make clean`` is executed. -To support the clean infrastructure in the Makefiles that build the -final bootimage there is an optional target named archclean: - - Example:: - - #arch/x86/Makefile - archclean: - $(Q)$(MAKE) $(clean)=arch/x86/boot - -When "make clean" is executed, make will descend down in arch/x86/boot, -and clean as usual. The Makefile located in arch/x86/boot/ may use -the subdir- trick to descend further down. - -Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is -included in the top level makefile, and the kbuild infrastructure -is not operational at that point. +Note 1: arch/$(SRCARCH)/Makefile cannot use ``subdir-``, because that file is +included in the top level makefile. Instead, arch/$(SRCARCH)/Kbuild can use +``subdir-``. Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will -be visited during "make clean". +be visited during ``make clean``. -6 Architecture Makefiles -======================== +Architecture Makefiles +====================== The top level Makefile sets up the environment and does the preparation, before starting to descend down in the individual directories. + The top level makefile contains the generic part, whereas -arch/$(ARCH)/Makefile contains what is required to set up kbuild +arch/$(SRCARCH)/Makefile contains what is required to set up kbuild for said architecture. -To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines + +To do so, arch/$(SRCARCH)/Makefile sets up a number of variables and defines a few targets. When kbuild executes, the following steps are followed (roughly): 1) Configuration of the kernel => produce .config + 2) Store kernel version in include/linux/version.h + 3) Updating all other prerequisites to the target prepare: - - Additional prerequisites are specified in arch/$(ARCH)/Makefile + + - Additional prerequisites are specified in arch/$(SRCARCH)/Makefile + 4) Recursively descend down in all directories listed in init-* core* drivers-* net-* libs-* and build all targets. - - The values of the above variables are expanded in arch/$(ARCH)/Makefile. + + - The values of the above variables are expanded in arch/$(SRCARCH)/Makefile. + 5) All object files are then linked and the resulting file vmlinux is located at the root of the obj tree. - The very first objects linked are listed in head-y, assigned by - arch/$(ARCH)/Makefile. + The very first objects linked are listed in scripts/head-object-list.txt. + 6) Finally, the architecture-specific part does any required post processing and builds the final bootimage. + - This includes building boot records - Preparing initrd images and the like +Set variables to tweak the build to the architecture +---------------------------------------------------- -6.1 Set variables to tweak the build to the architecture --------------------------------------------------------- - - LDFLAGS - Generic $(LD) options - - Flags used for all invocations of the linker. - Often specifying the emulation is sufficient. - - Example:: - - #arch/s390/Makefile - LDFLAGS := -m elf_s390 +KBUILD_LDFLAGS + Generic $(LD) options - Note: ldflags-y can be used to further customise - the flags used. See chapter 3.7. + Flags used for all invocations of the linker. + Often specifying the emulation is sufficient. - LDFLAGS_vmlinux - Options for $(LD) when linking vmlinux + Example:: - LDFLAGS_vmlinux is used to specify additional flags to pass to - the linker when linking the final vmlinux image. - LDFLAGS_vmlinux uses the LDFLAGS_$@ support. + #arch/s390/Makefile + KBUILD_LDFLAGS := -m elf_s390 - Example:: + Note: ldflags-y can be used to further customise + the flags used. See `Non-builtin vmlinux targets - extra-y`_. - #arch/x86/Makefile - LDFLAGS_vmlinux := -e stext +LDFLAGS_vmlinux + Options for $(LD) when linking vmlinux - OBJCOPYFLAGS - objcopy flags + LDFLAGS_vmlinux is used to specify additional flags to pass to + the linker when linking the final vmlinux image. - When $(call if_changed,objcopy) is used to translate a .o file, - the flags specified in OBJCOPYFLAGS will be used. - $(call if_changed,objcopy) is often used to generate raw binaries on - vmlinux. + LDFLAGS_vmlinux uses the LDFLAGS_$@ support. - Example:: + Example:: - #arch/s390/Makefile - OBJCOPYFLAGS := -O binary + #arch/x86/Makefile + LDFLAGS_vmlinux := -e stext - #arch/s390/boot/Makefile - $(obj)/image: vmlinux FORCE - $(call if_changed,objcopy) +OBJCOPYFLAGS + objcopy flags - In this example, the binary $(obj)/image is a binary version of - vmlinux. The usage of $(call if_changed,xxx) will be described later. + When $(call if_changed,objcopy) is used to translate a .o file, + the flags specified in OBJCOPYFLAGS will be used. - KBUILD_AFLAGS - Assembler flags + $(call if_changed,objcopy) is often used to generate raw binaries on + vmlinux. - Default value - see top level Makefile - Append or modify as required per architecture. + Example:: - Example:: + #arch/s390/Makefile + OBJCOPYFLAGS := -O binary - #arch/sparc64/Makefile - KBUILD_AFLAGS += -m64 -mcpu=ultrasparc + #arch/s390/boot/Makefile + $(obj)/image: vmlinux FORCE + $(call if_changed,objcopy) - KBUILD_CFLAGS - $(CC) compiler flags + In this example, the binary $(obj)/image is a binary version of + vmlinux. The usage of $(call if_changed,xxx) will be described later. - Default value - see top level Makefile - Append or modify as required per architecture. +KBUILD_AFLAGS + Assembler flags - Often, the KBUILD_CFLAGS variable depends on the configuration. + Default value - see top level Makefile. - Example:: + Append or modify as required per architecture. - #arch/x86/boot/compressed/Makefile - cflags-$(CONFIG_X86_32) := -march=i386 - cflags-$(CONFIG_X86_64) := -mcmodel=small - KBUILD_CFLAGS += $(cflags-y) + Example:: - Many arch Makefiles dynamically run the target C compiler to - probe supported options:: + #arch/sparc64/Makefile + KBUILD_AFLAGS += -m64 -mcpu=ultrasparc - #arch/x86/Makefile +KBUILD_CFLAGS + $(CC) compiler flags - ... - cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\ - -march=pentium2,-march=i686) - ... - # Disable unit-at-a-time mode ... - KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time) - ... - - - The first example utilises the trick that a config option expands - to 'y' when selected. - - KBUILD_AFLAGS_KERNEL - Assembler options specific for built-in - - $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile - resident kernel code. - - KBUILD_AFLAGS_MODULE - Assembler options specific for modules - - $(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that - are used for assembler. + Default value - see top level Makefile. - From commandline AFLAGS_MODULE shall be used (see kbuild.txt). + Append or modify as required per architecture. - KBUILD_CFLAGS_KERNEL - $(CC) options specific for built-in + Often, the KBUILD_CFLAGS variable depends on the configuration. - $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile - resident kernel code. + Example:: - KBUILD_CFLAGS_MODULE - Options for $(CC) when building modules + #arch/x86/boot/compressed/Makefile + cflags-$(CONFIG_X86_32) := -march=i386 + cflags-$(CONFIG_X86_64) := -mcmodel=small + KBUILD_CFLAGS += $(cflags-y) - $(KBUILD_CFLAGS_MODULE) is used to add arch-specific options that - are used for $(CC). - From commandline CFLAGS_MODULE shall be used (see kbuild.txt). + Many arch Makefiles dynamically run the target C compiler to + probe supported options:: - KBUILD_LDFLAGS_MODULE - Options for $(LD) when linking modules + #arch/x86/Makefile - $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options - used when linking modules. This is often a linker script. - - From commandline LDFLAGS_MODULE shall be used (see kbuild.txt). - - KBUILD_LDS + ... + cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\ + -march=pentium2,-march=i686) + ... + # Disable unit-at-a-time mode ... + KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time) + ... - The linker script with full path. Assigned by the top-level Makefile. - KBUILD_LDS_MODULE + The first example utilises the trick that a config option expands + to "y" when selected. - The module linker script with full path. Assigned by the top-level - Makefile and additionally by the arch Makefile. +KBUILD_RUSTFLAGS + $(RUSTC) compiler flags - KBUILD_VMLINUX_OBJS + Default value - see top level Makefile. - All object files for vmlinux. They are linked to vmlinux in the same - order as listed in KBUILD_VMLINUX_OBJS. + Append or modify as required per architecture. - KBUILD_VMLINUX_LIBS + Often, the KBUILD_RUSTFLAGS variable depends on the configuration. - All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and - KBUILD_VMLINUX_LIBS together specify all the object files used to - link vmlinux. + Note that target specification file generation (for ``--target``) + is handled in ``scripts/generate_rust_target.rs``. -6.2 Add prerequisites to archheaders ------------------------------------- +KBUILD_AFLAGS_KERNEL + Assembler options specific for built-in - The archheaders: rule is used to generate header files that - may be installed into user space by "make header_install". + $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile + resident kernel code. - It is run before "make archprepare" when run on the - architecture itself. +KBUILD_AFLAGS_MODULE + Assembler options specific for modules + $(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that + are used for assembler. -6.3 Add prerequisites to archprepare ------------------------------------- + From commandline AFLAGS_MODULE shall be used (see kbuild.rst). - The archprepare: rule is used to list prerequisites that need to be - built before starting to descend down in the subdirectories. - This is usually used for header files containing assembler constants. +KBUILD_CFLAGS_KERNEL + $(CC) options specific for built-in - Example:: + $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile + resident kernel code. - #arch/arm/Makefile - archprepare: maketools +KBUILD_CFLAGS_MODULE + Options for $(CC) when building modules - In this example, the file target maketools will be processed - before descending down in the subdirectories. - See also chapter XXX-TODO that describe how kbuild supports - generating offset header files. + $(KBUILD_CFLAGS_MODULE) is used to add arch-specific options that + are used for $(CC). + From commandline CFLAGS_MODULE shall be used (see kbuild.rst). -6.4 List directories to visit when descending ---------------------------------------------- +KBUILD_RUSTFLAGS_KERNEL + $(RUSTC) options specific for built-in - An arch Makefile cooperates with the top Makefile to define variables - which specify how to build the vmlinux file. Note that there is no - corresponding arch-specific section for modules; the module-building - machinery is all architecture-independent. + $(KBUILD_RUSTFLAGS_KERNEL) contains extra Rust compiler flags used to + compile resident kernel code. +KBUILD_RUSTFLAGS_MODULE + Options for $(RUSTC) when building modules - head-y, init-y, core-y, libs-y, drivers-y, net-y - $(head-y) lists objects to be linked first in vmlinux. + $(KBUILD_RUSTFLAGS_MODULE) is used to add arch-specific options that + are used for $(RUSTC). - $(libs-y) lists directories where a lib.a archive can be located. + From commandline RUSTFLAGS_MODULE shall be used (see kbuild.rst). - The rest list directories where a built-in.a object file can be - located. +KBUILD_LDFLAGS_MODULE + Options for $(LD) when linking modules - $(init-y) objects will be located after $(head-y). + $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options + used when linking modules. This is often a linker script. - Then the rest follows in this order: + From commandline LDFLAGS_MODULE shall be used (see kbuild.rst). - $(core-y), $(libs-y), $(drivers-y) and $(net-y). +KBUILD_LDS + The linker script with full path. Assigned by the top-level Makefile. - The top level Makefile defines values for all generic directories, - and arch/$(ARCH)/Makefile only adds architecture-specific - directories. +KBUILD_VMLINUX_OBJS + All object files for vmlinux. They are linked to vmlinux in the same + order as listed in KBUILD_VMLINUX_OBJS. - Example:: + The objects listed in scripts/head-object-list.txt are exceptions; + they are placed before the other objects. - #arch/sparc64/Makefile - core-y += arch/sparc64/kernel/ - libs-y += arch/sparc64/prom/ arch/sparc64/lib/ - drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/ +KBUILD_VMLINUX_LIBS + All .a ``lib`` files for vmlinux. KBUILD_VMLINUX_OBJS and + KBUILD_VMLINUX_LIBS together specify all the object files used to + link vmlinux. +Add prerequisites to archheaders +-------------------------------- -6.5 Architecture-specific boot images -------------------------------------- +The archheaders: rule is used to generate header files that +may be installed into user space by ``make header_install``. - An arch Makefile specifies goals that take the vmlinux file, compress - it, wrap it in bootstrapping code, and copy the resulting files - somewhere. This includes various kinds of installation commands. - The actual goals are not standardized across architectures. +It is run before ``make archprepare`` when run on the +architecture itself. - It is common to locate any additional processing in a boot/ - directory below arch/$(ARCH)/. +Add prerequisites to archprepare +-------------------------------- - Kbuild does not provide any smart way to support building a - target specified in boot/. Therefore arch/$(ARCH)/Makefile shall - call make manually to build a target in boot/. +The archprepare: rule is used to list prerequisites that need to be +built before starting to descend down in the subdirectories. - The recommended approach is to include shortcuts in - arch/$(ARCH)/Makefile, and use the full path when calling down - into the arch/$(ARCH)/boot/Makefile. +This is usually used for header files containing assembler constants. - Example:: +Example:: - #arch/x86/Makefile - boot := arch/x86/boot - bzImage: vmlinux - $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@ + #arch/arm/Makefile + archprepare: maketools - "$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke - make in a subdirectory. +In this example, the file target maketools will be processed +before descending down in the subdirectories. - There are no rules for naming architecture-specific targets, - but executing "make help" will list all relevant targets. - To support this, $(archhelp) must be defined. +See also chapter XXX-TODO that describes how kbuild supports +generating offset header files. - Example:: +List directories to visit when descending +----------------------------------------- - #arch/x86/Makefile - define archhelp - echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)' - endif +An arch Makefile cooperates with the top Makefile to define variables +which specify how to build the vmlinux file. Note that there is no +corresponding arch-specific section for modules; the module-building +machinery is all architecture-independent. - When make is executed without arguments, the first goal encountered - will be built. In the top level Makefile the first goal present - is all:. - An architecture shall always, per default, build a bootable image. - In "make help", the default goal is highlighted with a '*'. - Add a new prerequisite to all: to select a default goal different - from vmlinux. +core-y, libs-y, drivers-y + $(libs-y) lists directories where a lib.a archive can be located. - Example:: + The rest list directories where a built-in.a object file can be + located. - #arch/x86/Makefile - all: bzImage + Then the rest follows in this order: - When "make" is executed without arguments, bzImage will be built. + $(core-y), $(libs-y), $(drivers-y) -6.6 Building non-kbuild targets -------------------------------- + The top level Makefile defines values for all generic directories, + and arch/$(SRCARCH)/Makefile only adds architecture-specific + directories. - extra-y - extra-y specifies additional targets created in the current - directory, in addition to any targets specified by `obj-*`. + Example:: - Listing all targets in extra-y is required for two purposes: + # arch/sparc/Makefile + core-y += arch/sparc/ - 1) Enable kbuild to check changes in command lines + libs-y += arch/sparc/prom/ + libs-y += arch/sparc/lib/ - - When $(call if_changed,xxx) is used + drivers-$(CONFIG_PM) += arch/sparc/power/ - 2) kbuild knows what files to delete during "make clean" +Architecture-specific boot images +--------------------------------- - Example:: +An arch Makefile specifies goals that take the vmlinux file, compress +it, wrap it in bootstrapping code, and copy the resulting files +somewhere. This includes various kinds of installation commands. +The actual goals are not standardized across architectures. - #arch/x86/kernel/Makefile - extra-y := head.o init_task.o +It is common to locate any additional processing in a boot/ +directory below arch/$(SRCARCH)/. - In this example, extra-y is used to list object files that - shall be built, but shall not be linked as part of built-in.a. +Kbuild does not provide any smart way to support building a +target specified in boot/. Therefore arch/$(SRCARCH)/Makefile shall +call make manually to build a target in boot/. -6.7 Commands useful for building a boot image ---------------------------------------------- +The recommended approach is to include shortcuts in +arch/$(SRCARCH)/Makefile, and use the full path when calling down +into the arch/$(SRCARCH)/boot/Makefile. - Kbuild provides a few macros that are useful when building a - boot image. +Example:: - if_changed - if_changed is the infrastructure used for the following commands. + #arch/x86/Makefile + boot := arch/x86/boot + bzImage: vmlinux + $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@ - Usage:: +``$(Q)$(MAKE) $(build)=<dir>`` is the recommended way to invoke +make in a subdirectory. - target: source(s) FORCE - $(call if_changed,ld/objcopy/gzip/...) +There are no rules for naming architecture-specific targets, +but executing ``make help`` will list all relevant targets. +To support this, $(archhelp) must be defined. - When the rule is evaluated, it is checked to see if any files - need an update, or the command line has changed since the last - invocation. The latter will force a rebuild if any options - to the executable have changed. - Any target that utilises if_changed must be listed in $(targets), - otherwise the command line check will fail, and the target will - always be built. - Assignments to $(targets) are without $(obj)/ prefix. - if_changed may be used in conjunction with custom commands as - defined in 6.8 "Custom kbuild commands". +Example:: - Note: It is a typical mistake to forget the FORCE prerequisite. - Another common pitfall is that whitespace is sometimes - significant; for instance, the below will fail (note the extra space - after the comma):: + #arch/x86/Makefile + define archhelp + echo '* bzImage - Compressed kernel image (arch/x86/boot/bzImage)' + endif - target: source(s) FORCE +When make is executed without arguments, the first goal encountered +will be built. In the top level Makefile the first goal present +is all:. - **WRONG!** $(call if_changed, ld/objcopy/gzip/...) +An architecture shall always, per default, build a bootable image. +In ``make help``, the default goal is highlighted with a ``*``. - Note: - if_changed should not be used more than once per target. - It stores the executed command in a corresponding .cmd +Add a new prerequisite to all: to select a default goal different +from vmlinux. - file and multiple calls would result in overwrites and - unwanted results when the target is up to date and only the - tests on changed commands trigger execution of commands. +Example:: - ld - Link target. Often, LDFLAGS_$@ is used to set specific options to ld. + #arch/x86/Makefile + all: bzImage - Example:: +When ``make`` is executed without arguments, bzImage will be built. - #arch/x86/boot/Makefile - LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary - LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext +Commands useful for building a boot image +----------------------------------------- - targets += setup setup.o bootsect bootsect.o - $(obj)/setup $(obj)/bootsect: %: %.o FORCE - $(call if_changed,ld) +Kbuild provides a few macros that are useful when building a +boot image. - In this example, there are two possible targets, requiring different - options to the linker. The linker options are specified using the - LDFLAGS_$@ syntax - one for each potential target. - $(targets) are assigned all potential targets, by which kbuild knows - the targets and will: +ld + Link target. Often, LDFLAGS_$@ is used to set specific options to ld. - 1) check for commandline changes - 2) delete target during make clean + Example:: - The ": %: %.o" part of the prerequisite is a shorthand that - frees us from listing the setup.o and bootsect.o files. + #arch/x86/boot/Makefile + LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary + LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext - Note: - It is a common mistake to forget the "targets :=" assignment, - resulting in the target file being recompiled for no - obvious reason. + targets += setup setup.o bootsect bootsect.o + $(obj)/setup $(obj)/bootsect: %: %.o FORCE + $(call if_changed,ld) - objcopy - Copy binary. Uses OBJCOPYFLAGS usually specified in - arch/$(ARCH)/Makefile. - OBJCOPYFLAGS_$@ may be used to set additional options. + In this example, there are two possible targets, requiring different + options to the linker. The linker options are specified using the + LDFLAGS_$@ syntax - one for each potential target. - gzip - Compress target. Use maximum compression to compress target. + $(targets) are assigned all potential targets, by which kbuild knows + the targets and will: - Example:: + 1) check for commandline changes + 2) delete target during make clean - #arch/x86/boot/compressed/Makefile - $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE - $(call if_changed,gzip) + The ``: %: %.o`` part of the prerequisite is a shorthand that + frees us from listing the setup.o and bootsect.o files. - dtc - Create flattened device tree blob object suitable for linking - into vmlinux. Device tree blobs linked into vmlinux are placed - in an init section in the image. Platform code *must* copy the - blob to non-init memory prior to calling unflatten_device_tree(). + Note: + It is a common mistake to forget the ``targets :=`` assignment, + resulting in the target file being recompiled for no + obvious reason. - To use this command, simply add `*.dtb` into obj-y or targets, or make - some other target depend on `%.dtb` +objcopy + Copy binary. Uses OBJCOPYFLAGS usually specified in + arch/$(SRCARCH)/Makefile. - A central rule exists to create `$(obj)/%.dtb` from `$(src)/%.dts`; - architecture Makefiles do no need to explicitly write out that rule. + OBJCOPYFLAGS_$@ may be used to set additional options. - Example:: +gzip + Compress target. Use maximum compression to compress target. - targets += $(dtb-y) - DTC_FLAGS ?= -p 1024 + Example:: -6.8 Custom kbuild commands --------------------------- + #arch/x86/boot/compressed/Makefile + $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE + $(call if_changed,gzip) - When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand - of a command is normally displayed. - To enable this behaviour for custom commands kbuild requires - two variables to be set:: +dtc + Create flattened device tree blob object suitable for linking + into vmlinux. Device tree blobs linked into vmlinux are placed + in an init section in the image. Platform code *must* copy the + blob to non-init memory prior to calling unflatten_device_tree(). - quiet_cmd_<command> - what shall be echoed - cmd_<command> - the command to execute + To use this command, simply add ``*.dtb`` into obj-y or targets, or make + some other target depend on ``%.dtb`` - Example:: + A central rule exists to create ``$(obj)/%.dtb`` from ``$(src)/%.dts``; + architecture Makefiles do no need to explicitly write out that rule. - # - quiet_cmd_image = BUILD $@ - cmd_image = $(obj)/tools/build $(BUILDFLAGS) \ - $(obj)/vmlinux.bin > $@ + Example:: - targets += bzImage - $(obj)/bzImage: $(obj)/vmlinux.bin $(obj)/tools/build FORCE - $(call if_changed,image) - @echo 'Kernel: $@ is ready' + targets += $(dtb-y) + DTC_FLAGS ?= -p 1024 - When updating the $(obj)/bzImage target, the line: +Preprocessing linker scripts +---------------------------- - BUILD arch/x86/boot/bzImage +When the vmlinux image is built, the linker script +arch/$(SRCARCH)/kernel/vmlinux.lds is used. - will be displayed with "make KBUILD_VERBOSE=0". +The script is a preprocessed variant of the file vmlinux.lds.S +located in the same directory. +kbuild knows .lds files and includes a rule ``*lds.S`` -> ``*lds``. ---- 6.9 Preprocessing linker scripts +Example:: - When the vmlinux image is built, the linker script - arch/$(ARCH)/kernel/vmlinux.lds is used. - The script is a preprocessed variant of the file vmlinux.lds.S - located in the same directory. - kbuild knows .lds files and includes a rule `*lds.S` -> `*lds`. + #arch/x86/kernel/Makefile + extra-y := vmlinux.lds - Example:: +The assignment to extra-y is used to tell kbuild to build the +target vmlinux.lds. - #arch/x86/kernel/Makefile - always := vmlinux.lds +The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the +specified options when building the target vmlinux.lds. - #Makefile - export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH) +When building the ``*.lds`` target, kbuild uses the variables:: - The assignment to $(always) is used to tell kbuild to build the - target vmlinux.lds. - The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the - specified options when building the target vmlinux.lds. + KBUILD_CPPFLAGS : Set in top-level Makefile + cppflags-y : May be set in the kbuild makefile + CPPFLAGS_$(@F) : Target-specific flags. + Note that the full filename is used in this + assignment. - When building the `*.lds` target, kbuild uses the variables:: +The kbuild infrastructure for ``*lds`` files is used in several +architecture-specific files. - KBUILD_CPPFLAGS : Set in top-level Makefile - cppflags-y : May be set in the kbuild makefile - CPPFLAGS_$(@F) : Target-specific flags. - Note that the full filename is used in this - assignment. +Generic header files +-------------------- - The kbuild infrastructure for `*lds` files is used in several - architecture-specific files. +The directory include/asm-generic contains the header files +that may be shared between individual architectures. -6.10 Generic header files -------------------------- +The recommended approach how to use a generic header file is +to list the file in the Kbuild file. - The directory include/asm-generic contains the header files - that may be shared between individual architectures. - The recommended approach how to use a generic header file is - to list the file in the Kbuild file. - See "7.2 generic-y" for further info on syntax etc. +See `generic-y`_ for further info on syntax etc. -6.11 Post-link pass -------------------- +Post-link pass +-------------- - If the file arch/xxx/Makefile.postlink exists, this makefile - will be invoked for post-link objects (vmlinux and modules.ko) - for architectures to run post-link passes on. Must also handle - the clean target. +If the file arch/xxx/Makefile.postlink exists, this makefile +will be invoked for post-link objects (vmlinux and modules.ko) +for architectures to run post-link passes on. Must also handle +the clean target. - This pass runs after kallsyms generation. If the architecture - needs to modify symbol locations, rather than manipulate the - kallsyms, it may be easier to add another postlink target for - .tmp_vmlinux? targets to be called from link-vmlinux.sh. +This pass runs after kallsyms generation. If the architecture +needs to modify symbol locations, rather than manipulate the +kallsyms, it may be easier to add another postlink target for +.tmp_vmlinux? targets to be called from link-vmlinux.sh. - For example, powerpc uses this to check relocation sanity of - the linked vmlinux file. +For example, powerpc uses this to check relocation sanity of +the linked vmlinux file. -7 Kbuild syntax for exported headers ------------------------------------- +Kbuild syntax for exported headers +================================== The kernel includes a set of headers that is exported to userspace. Many headers can be exported as-is but other headers require a minimal pre-processing before they are ready for user-space. + The pre-processing does: - drop kernel-specific annotations - drop include of compiler.h -- drop all sections that are kernel internal (guarded by `ifdef __KERNEL__`) +- drop all sections that are kernel internal (guarded by ``ifdef __KERNEL__``) All headers under include/uapi/, include/generated/uapi/, arch/<arch>/include/uapi/ and arch/<arch>/include/generated/uapi/ @@ -1323,132 +1496,146 @@ are exported. A Kbuild file may be defined under arch/<arch>/include/uapi/asm/ and arch/<arch>/include/asm/ to list asm files coming from asm-generic. -See subsequent chapter for the syntax of the Kbuild file. -7.1 no-export-headers ---------------------- +See subsequent chapter for the syntax of the Kbuild file. - no-export-headers is essentially used by include/uapi/linux/Kbuild to - avoid exporting specific headers (e.g. kvm.h) on architectures that do - not support it. It should be avoided as much as possible. +no-export-headers +----------------- -7.2 generic-y -------------- +no-export-headers is essentially used by include/uapi/linux/Kbuild to +avoid exporting specific headers (e.g. kvm.h) on architectures that do +not support it. It should be avoided as much as possible. - If an architecture uses a verbatim copy of a header from - include/asm-generic then this is listed in the file - arch/$(ARCH)/include/asm/Kbuild like this: +generic-y +--------- - Example:: +If an architecture uses a verbatim copy of a header from +include/asm-generic then this is listed in the file +arch/$(SRCARCH)/include/asm/Kbuild like this: - #arch/x86/include/asm/Kbuild - generic-y += termios.h - generic-y += rtc.h +Example:: - During the prepare phase of the build a wrapper include - file is generated in the directory:: + #arch/x86/include/asm/Kbuild + generic-y += termios.h + generic-y += rtc.h - arch/$(ARCH)/include/generated/asm +During the prepare phase of the build a wrapper include +file is generated in the directory:: - When a header is exported where the architecture uses - the generic header a similar wrapper is generated as part - of the set of exported headers in the directory:: + arch/$(SRCARCH)/include/generated/asm - usr/include/asm +When a header is exported where the architecture uses +the generic header a similar wrapper is generated as part +of the set of exported headers in the directory:: - The generated wrapper will in both cases look like the following: + usr/include/asm - Example: termios.h:: +The generated wrapper will in both cases look like the following: - #include <asm-generic/termios.h> +Example: termios.h:: -7.3 generated-y ---------------- + #include <asm-generic/termios.h> - If an architecture generates other header files alongside generic-y - wrappers, generated-y specifies them. +generated-y +----------- - This prevents them being treated as stale asm-generic wrappers and - removed. +If an architecture generates other header files alongside generic-y +wrappers, generated-y specifies them. - Example:: +This prevents them being treated as stale asm-generic wrappers and +removed. - #arch/x86/include/asm/Kbuild - generated-y += syscalls_32.h +Example:: -7.4 mandatory-y ---------------- + #arch/x86/include/asm/Kbuild + generated-y += syscalls_32.h - mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild - to define the minimum set of ASM headers that all architectures must have. +mandatory-y +----------- - This works like optional generic-y. If a mandatory header is missing - in arch/$(ARCH)/include/(uapi/)/asm, Kbuild will automatically generate - a wrapper of the asm-generic one. +mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild +to define the minimum set of ASM headers that all architectures must have. - The convention is to list one subdir per line and - preferably in alphabetic order. +This works like optional generic-y. If a mandatory header is missing +in arch/$(SRCARCH)/include/(uapi/)/asm, Kbuild will automatically +generate a wrapper of the asm-generic one. -8 Kbuild Variables -================== +Kbuild Variables +================ The top Makefile exports the following variables: - VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION - These variables define the current kernel version. A few arch - Makefiles actually use these values directly; they should use - $(KERNELRELEASE) instead. - - $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic - three-part version number, such as "2", "4", and "0". These three - values are always numeric. - - $(EXTRAVERSION) defines an even tinier sublevel for pre-patches - or additional patches. It is usually some non-numeric string - such as "-pre4", and is often blank. - - KERNELRELEASE - $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable - for constructing installation directory names or showing in - version strings. Some arch Makefiles use it for this purpose. - - ARCH - This variable defines the target architecture, such as "i386", - "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to - determine which files to compile. - - By default, the top Makefile sets $(ARCH) to be the same as the - host system architecture. For a cross build, a user may - override the value of $(ARCH) on the command line:: - - make ARCH=m68k ... - - - INSTALL_PATH - This variable defines a place for the arch Makefiles to install - the resident kernel image and System.map file. - Use this for architecture-specific install targets. - - INSTALL_MOD_PATH, MODLIB - $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module - installation. This variable is not defined in the Makefile but - may be passed in by the user if desired. - - $(MODLIB) specifies the directory for module installation. - The top Makefile defines $(MODLIB) to - $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may - override this value on the command line if desired. - - INSTALL_MOD_STRIP - If this variable is specified, it will cause modules to be stripped - after they are installed. If INSTALL_MOD_STRIP is '1', then the - default option --strip-debug will be used. Otherwise, the - INSTALL_MOD_STRIP value will be used as the option(s) to the strip - command. - - -9 Makefile language -=================== +VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION + These variables define the current kernel version. A few arch + Makefiles actually use these values directly; they should use + $(KERNELRELEASE) instead. + + $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic + three-part version number, such as "2", "4", and "0". These three + values are always numeric. + + $(EXTRAVERSION) defines an even tinier sublevel for pre-patches + or additional patches. It is usually some non-numeric string + such as "-pre4", and is often blank. + +KERNELRELEASE + $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable + for constructing installation directory names or showing in + version strings. Some arch Makefiles use it for this purpose. + +ARCH + This variable defines the target architecture, such as "i386", + "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to + determine which files to compile. + + By default, the top Makefile sets $(ARCH) to be the same as the + host system architecture. For a cross build, a user may + override the value of $(ARCH) on the command line:: + + make ARCH=m68k ... + +SRCARCH + This variable specifies the directory in arch/ to build. + + ARCH and SRCARCH may not necessarily match. A couple of arch + directories are biarch, that is, a single ``arch/*/`` directory supports + both 32-bit and 64-bit. + + For example, you can pass in ARCH=i386, ARCH=x86_64, or ARCH=x86. + For all of them, SRCARCH=x86 because arch/x86/ supports both i386 and + x86_64. + +INSTALL_PATH + This variable defines a place for the arch Makefiles to install + the resident kernel image and System.map file. + Use this for architecture-specific install targets. + +INSTALL_MOD_PATH, MODLIB + $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module + installation. This variable is not defined in the Makefile but + may be passed in by the user if desired. + + $(MODLIB) specifies the directory for module installation. + The top Makefile defines $(MODLIB) to + $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may + override this value on the command line if desired. + +INSTALL_MOD_STRIP + If this variable is specified, it will cause modules to be stripped + after they are installed. If INSTALL_MOD_STRIP is "1", then the + default option --strip-debug will be used. Otherwise, the + INSTALL_MOD_STRIP value will be used as the option(s) to the strip + command. + +INSTALL_DTBS_PATH + This variable specifies a prefix for relocations required by build + roots. It defines a place for installing the device tree blobs. Like + INSTALL_MOD_PATH, it isn't defined in the Makefile, but can be passed + by the user if desired. Otherwise it defaults to the kernel install + path. + +Makefile language +================= The kernel Makefiles are designed to be run with GNU Make. The Makefiles use only the documented features of GNU Make, but they do use many @@ -1456,28 +1643,28 @@ GNU extensions. GNU Make supports elementary list-processing functions. The kernel Makefiles use a novel style of list building and manipulation with few -"if" statements. +``if`` statements. -GNU Make has two assignment operators, ":=" and "=". ":=" performs +GNU Make has two assignment operators, ``:=`` and ``=``. ``:=`` performs immediate evaluation of the right-hand side and stores an actual string -into the left-hand side. "=" is like a formula definition; it stores the +into the left-hand side. ``=`` is like a formula definition; it stores the right-hand side in an unevaluated form and then evaluates this form each time the left-hand side is used. -There are some cases where "=" is appropriate. Usually, though, ":=" +There are some cases where ``=`` is appropriate. Usually, though, ``:=`` is the right choice. -10 Credits -========== +Credits +======= - Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net> - Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de> - Updates by Sam Ravnborg <sam@ravnborg.org> - Language QA by Jan Engelhardt <jengelh@gmx.de> -11 TODO -======= +TODO +==== - Describe how kbuild supports shipped files with _shipped. - Generating offset header files. -- Add more variables to section 7? +- Add more variables to chapters 7 or 9? diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst index 69fa48ee93d6..a1f3eb7a43e2 100644 --- a/Documentation/kbuild/modules.rst +++ b/Documentation/kbuild/modules.rst @@ -182,7 +182,8 @@ module 8123.ko, which is built from the following files:: 8123_pci.c 8123_bin.o_shipped <= Binary blob ---- 3.1 Shared Makefile +3.1 Shared Makefile +------------------- An external module always includes a wrapper makefile that supports building the module using "make" with no arguments. @@ -331,7 +332,7 @@ according to the following rule: There are two notable exceptions to this rule: larger subsystems have their own directory under include/, such as include/scsi; and architecture specific headers are located - under arch/$(ARCH)/include/. + under arch/$(SRCARCH)/include/. 4.1 Kernel Includes ------------------- @@ -470,9 +471,9 @@ build. The syntax of the Module.symvers file is:: - <CRC> <Symbol> <Namespace> <Module> <Export Type> + <CRC> <Symbol> <Module> <Export Type> <Namespace> - 0xe1cc2a05 usb_stor_suspend USB_STORAGE drivers/usb/storage/usb-storage EXPORT_SYMBOL_GPL + 0xe1cc2a05 usb_stor_suspend drivers/usb/storage/usb-storage EXPORT_SYMBOL_GPL USB_STORAGE The fields are separated by tabs and values may be empty (e.g. if no namespace is defined for an exported symbol). @@ -528,18 +529,6 @@ build. will then do the expected and compile both modules with full knowledge of symbols from either module. - Use an extra Module.symvers file - When an external module is built, a Module.symvers file - is generated containing all exported symbols which are - not defined in the kernel. To get access to symbols - from bar.ko, copy the Module.symvers file from the - compilation of bar.ko to the directory where foo.ko is - built. During the module build, kbuild will read the - Module.symvers file in the directory of the external - module, and when the build is finished, a new - Module.symvers file is created containing the sum of - all symbols defined and not part of the kernel. - Use "make" variable KBUILD_EXTRA_SYMBOLS If it is impractical to add a top-level kbuild file, you can assign a space separated list diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst index 503393854e2e..f2dcc39044e6 100644 --- a/Documentation/kbuild/reproducible-builds.rst +++ b/Documentation/kbuild/reproducible-builds.rst @@ -99,10 +99,10 @@ unreproducible parts can be treated as sources: Structure randomisation ----------------------- -If you enable ``CONFIG_GCC_PLUGIN_RANDSTRUCT``, you will need to -pre-generate the random seed in -``scripts/gcc-plgins/randomize_layout_seed.h`` so the same value -is used in rebuilds. +If you enable ``CONFIG_RANDSTRUCT``, you will need to pre-generate +the random seed in ``scripts/basic/randstruct.seed`` so the same +value is used by each build. See ``scripts/gen-randstruct-seed.sh`` +for details. Debug info conflicts -------------------- @@ -119,6 +119,16 @@ To avoid this, you can make the vDSO different for different kernel versions by including an arbitrary string of "salt" in it. This is specified by the Kconfig symbol ``CONFIG_BUILD_SALT``. +Git +--- + +Uncommitted changes or different commit ids in git can also lead +to different compilation results. For example, after executing +``git reset HEAD^``, even if the code is the same, the +``include/config/kernel.release`` generated during compilation +will be different, which will eventually lead to binary differences. +See ``scripts/setlocalversion`` for details. + .. _KBUILD_BUILD_TIMESTAMP: kbuild.html#kbuild-build-timestamp .. _KBUILD_BUILD_USER and KBUILD_BUILD_HOST: kbuild.html#kbuild-build-user-kbuild-build-host .. _KCFLAGS: kbuild.html#kcflags |