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Diffstat (limited to 'Documentation/kbuild/makefiles.rst')
| -rw-r--r-- | Documentation/kbuild/makefiles.rst | 71 |
1 files changed, 55 insertions, 16 deletions
diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst index e67eb261c9b0..8aef3650c1f3 100644 --- a/Documentation/kbuild/makefiles.rst +++ b/Documentation/kbuild/makefiles.rst @@ -53,7 +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. @@ -291,6 +291,10 @@ Example:: # arch/x86/kernel/Makefile extra-y += vmlinux.lds +extra-y is now deprecated because this is equivalent to: + + always-$(KBUILD_BUILTIN) += vmlinux.lds + $(extra-y) should only contain targets needed for vmlinux. Kbuild skips extra-y when vmlinux is apparently not a final goal. @@ -318,9 +322,6 @@ 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). @@ -346,7 +347,7 @@ ccflags-y, asflags-y and ldflags-y Example:: #arch/cris/boot/compressed/Makefile - ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds + ldflags-y += -T $(src)/decompress_$(arch-y).lds subdir-ccflags-y, subdir-asflags-y The two flags listed above are similar to ccflags-y and asflags-y. @@ -426,14 +427,14 @@ 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 + $(src) is 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. + $(obj) is the directory where the target is saved. Always use $(obj) when + referring to generated files. Use $(obj) for pattern rules that need to work + for both generated files and real sources (VPATH will help to find the + prerequisites not only in the object tree but also in the source tree). Example:: @@ -449,6 +450,20 @@ $(obj) to prerequisites are referenced with $(src) (because they are not generated files). +$(srcroot) + $(srcroot) refers to the root of the source you are building, which can be + either the kernel source or the external modules source, depending on whether + KBUILD_EXTMOD is set. This can be either a relative or an absolute path, but + if KBUILD_ABS_SRCTREE=1 is set, it is always an absolute path. + +$(srctree) + $(srctree) refers to the root of the kernel source tree. When building the + kernel, this is the same as $(srcroot). + +$(objtree) + $(objtree) refers to the root of the kernel object tree. It is ``.`` when + building the kernel, but it is different when building external modules. + $(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 @@ -578,7 +593,7 @@ cc-option 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 + cc-option-yn is used to check if $(CC) supports a given option and return "y" if supported, otherwise "n". Example:: @@ -596,7 +611,7 @@ cc-option-yn 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 + cc-disable-warning checks if $(CC) 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. @@ -606,7 +621,7 @@ cc-disable-warning 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. + KBUILD_CFLAGS only if $(CC) really accepts it. gcc-min-version gcc-min-version tests if the value of $(CONFIG_GCC_VERSION) is greater than @@ -614,10 +629,10 @@ gcc-min-version Example:: - cflags-$(call gcc-min-version, 70100) := -foo + cflags-$(call gcc-min-version, 110100) := -foo In this example, cflags-y will be assigned the value -foo if $(CC) is gcc and - $(CONFIG_GCC_VERSION) is >= 7.1. + $(CONFIG_GCC_VERSION) is >= 11.1. clang-min-version clang-min-version tests if the value of $(CONFIG_CLANG_VERSION) is greater @@ -656,6 +671,20 @@ cc-cross-prefix endif endif +$(RUSTC) support functions +-------------------------- + +rustc-min-version + rustc-min-version tests if the value of $(CONFIG_RUSTC_VERSION) is greater + than or equal to the provided value and evaluates to y if so. + + Example:: + + rustflags-$(call rustc-min-version, 108500) := -Cfoo + + In this example, rustflags-y will be assigned the value -Cfoo if + $(CONFIG_RUSTC_VERSION) is >= 1.85.0. + $(LD) support functions ----------------------- @@ -937,6 +966,10 @@ 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. @@ -1623,6 +1656,13 @@ INSTALL_MOD_STRIP 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 ================= @@ -1654,6 +1694,5 @@ Credits TODO ==== -- Describe how kbuild supports shipped files with _shipped. - Generating offset header files. - Add more variables to chapters 7 or 9? |