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diff --git a/tools/bpf/bpftool/Documentation/bpftool-gen.rst b/tools/bpf/bpftool/Documentation/bpftool-gen.rst new file mode 100644 index 000000000000..d0a36f442db7 --- /dev/null +++ b/tools/bpf/bpftool/Documentation/bpftool-gen.rst @@ -0,0 +1,481 @@ +.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) + +================ +bpftool-gen +================ +------------------------------------------------------------------------------- +tool for BPF code-generation +------------------------------------------------------------------------------- + +:Manual section: 8 + +.. include:: substitutions.rst + +SYNOPSIS +======== + +**bpftool** [*OPTIONS*] **gen** *COMMAND* + +*OPTIONS* := { |COMMON_OPTIONS| | { **-L** | **--use-loader** } | [ { **-S** | **--sign** } {**-k** <private_key.pem>} **-i** <certificate.x509> ] } + +*COMMAND* := { **object** | **skeleton** | **help** } + +GEN COMMANDS +============= + +| **bpftool** **gen object** *OUTPUT_FILE* *INPUT_FILE* [*INPUT_FILE*...] +| **bpftool** **gen skeleton** *FILE* [**name** *OBJECT_NAME*] +| **bpftool** **gen subskeleton** *FILE* [**name** *OBJECT_NAME*] +| **bpftool** **gen min_core_btf** *INPUT* *OUTPUT* *OBJECT* [*OBJECT*...] +| **bpftool** **gen help** + +DESCRIPTION +=========== +bpftool gen object *OUTPUT_FILE* *INPUT_FILE* [*INPUT_FILE*...] + Statically link (combine) together one or more *INPUT_FILE*'s into a single + resulting *OUTPUT_FILE*. All the files involved are BPF ELF object files. + + The rules of BPF static linking are mostly the same as for user-space + object files, but in addition to combining data and instruction sections, + .BTF and .BTF.ext (if present in any of the input files) data are combined + together. .BTF data is deduplicated, so all the common types across + *INPUT_FILE*'s will only be represented once in the resulting BTF + information. + + BPF static linking allows to partition BPF source code into individually + compiled files that are then linked into a single resulting BPF object + file, which can be used to generated BPF skeleton (with **gen skeleton** + command) or passed directly into **libbpf** (using **bpf_object__open()** + family of APIs). + +bpftool gen skeleton *FILE* + Generate BPF skeleton C header file for a given *FILE*. + + BPF skeleton is an alternative interface to existing libbpf APIs for + working with BPF objects. Skeleton code is intended to significantly + shorten and simplify code to load and work with BPF programs from userspace + side. Generated code is tailored to specific input BPF object *FILE*, + reflecting its structure by listing out available maps, program, variables, + etc. Skeleton eliminates the need to lookup mentioned components by name. + Instead, if skeleton instantiation succeeds, they are populated in skeleton + structure as valid libbpf types (e.g., **struct bpf_map** pointer) and can + be passed to existing generic libbpf APIs. + + In addition to simple and reliable access to maps and programs, skeleton + provides a storage for BPF links (**struct bpf_link**) for each BPF program + within BPF object. When requested, supported BPF programs will be + automatically attached and resulting BPF links stored for further use by + user in pre-allocated fields in skeleton struct. For BPF programs that + can't be automatically attached by libbpf, user can attach them manually, + but store resulting BPF link in per-program link field. All such set up + links will be automatically destroyed on BPF skeleton destruction. This + eliminates the need for users to manage links manually and rely on libbpf + support to detach programs and free up resources. + + Another facility provided by BPF skeleton is an interface to global + variables of all supported kinds: mutable, read-only, as well as extern + ones. This interface allows to pre-setup initial values of variables before + BPF object is loaded and verified by kernel. For non-read-only variables, + the same interface can be used to fetch values of global variables on + userspace side, even if they are modified by BPF code. + + During skeleton generation, contents of source BPF object *FILE* is + embedded within generated code and is thus not necessary to keep around. + This ensures skeleton and BPF object file are matching 1-to-1 and always + stay in sync. Generated code is dual-licensed under LGPL-2.1 and + BSD-2-Clause licenses. + + It is a design goal and guarantee that skeleton interfaces are + interoperable with generic libbpf APIs. User should always be able to use + skeleton API to create and load BPF object, and later use libbpf APIs to + keep working with specific maps, programs, etc. + + As part of skeleton, few custom functions are generated. Each of them is + prefixed with object name. Object name can either be derived from object + file name, i.e., if BPF object file name is **example.o**, BPF object name + will be **example**. Object name can be also specified explicitly through + **name** *OBJECT_NAME* parameter. The following custom functions are + provided (assuming **example** as the object name): + + - **example__open** and **example__open_opts**. + These functions are used to instantiate skeleton. It corresponds to + libbpf's **bpf_object__open**\ () API. **_opts** variants accepts extra + **bpf_object_open_opts** options. + + - **example__load**. + This function creates maps, loads and verifies BPF programs, initializes + global data maps. It corresponds to libbpf's **bpf_object__load**\ () + API. + + - **example__open_and_load** combines **example__open** and + **example__load** invocations in one commonly used operation. + + - **example__attach** and **example__detach**. + This pair of functions allow to attach and detach, correspondingly, + already loaded BPF object. Only BPF programs of types supported by libbpf + for auto-attachment will be auto-attached and their corresponding BPF + links instantiated. For other BPF programs, user can manually create a + BPF link and assign it to corresponding fields in skeleton struct. + **example__detach** will detach both links created automatically, as well + as those populated by user manually. + + - **example__destroy**. + Detach and unload BPF programs, free up all the resources used by + skeleton and BPF object. + + If BPF object has global variables, corresponding structs with memory + layout corresponding to global data data section layout will be created. + Currently supported ones are: *.data*, *.bss*, *.rodata*, and *.kconfig* + structs/data sections. These data sections/structs can be used to set up + initial values of variables, if set before **example__load**. Afterwards, + if target kernel supports memory-mapped BPF arrays, same structs can be + used to fetch and update (non-read-only) data from userspace, with same + simplicity as for BPF side. + +bpftool gen subskeleton *FILE* + Generate BPF subskeleton C header file for a given *FILE*. + + Subskeletons are similar to skeletons, except they do not own the + corresponding maps, programs, or global variables. They require that the + object file used to generate them is already loaded into a *bpf_object* by + some other means. + + This functionality is useful when a library is included into a larger BPF + program. A subskeleton for the library would have access to all objects and + globals defined in it, without having to know about the larger program. + + Consequently, there are only two functions defined for subskeletons: + + - **example__open(bpf_object\*)**. + Instantiates a subskeleton from an already opened (but not necessarily + loaded) **bpf_object**. + + - **example__destroy()**. + Frees the storage for the subskeleton but *does not* unload any BPF + programs or maps. + +bpftool gen min_core_btf *INPUT* *OUTPUT* *OBJECT* [*OBJECT*...] + Generate a minimum BTF file as *OUTPUT*, derived from a given *INPUT* BTF + file, containing all needed BTF types so one, or more, given eBPF objects + CO-RE relocations may be satisfied. + + When kernels aren't compiled with CONFIG_DEBUG_INFO_BTF, libbpf, when + loading an eBPF object, has to rely on external BTF files to be able to + calculate CO-RE relocations. + + Usually, an external BTF file is built from existing kernel DWARF data + using pahole. It contains all the types used by its respective kernel image + and, because of that, is big. + + The min_core_btf feature builds smaller BTF files, customized to one or + multiple eBPF objects, so they can be distributed together with an eBPF + CO-RE based application, turning the application portable to different + kernel versions. + + Check examples below for more information on how to use it. + +bpftool gen help + Print short help message. + +OPTIONS +======= +.. include:: common_options.rst + +-L, --use-loader + For skeletons, generate a "light" skeleton (also known as "loader" + skeleton). A light skeleton contains a loader eBPF program. It does not use + the majority of the libbpf infrastructure, and does not need libelf. + +-S, --sign + For skeletons, generate a signed skeleton. This option must be used with + **-k** and **-i**. Using this flag implicitly enables **--use-loader**. + +-k <private_key.pem> + Path to the private key file in PEM format, required for signing. + +-i <certificate.x509> + Path to the X.509 certificate file in PEM or DER format, required for + signing. + +EXAMPLES +======== +**$ cat example1.bpf.c** + +:: + + #include <stdbool.h> + #include <linux/ptrace.h> + #include <linux/bpf.h> + #include <bpf/bpf_helpers.h> + + const volatile int param1 = 42; + bool global_flag = true; + struct { int x; } data = {}; + + SEC("raw_tp/sys_enter") + int handle_sys_enter(struct pt_regs *ctx) + { + static long my_static_var; + if (global_flag) + my_static_var++; + else + data.x += param1; + return 0; + } + +**$ cat example2.bpf.c** + +:: + + #include <linux/ptrace.h> + #include <linux/bpf.h> + #include <bpf/bpf_helpers.h> + + struct { + __uint(type, BPF_MAP_TYPE_HASH); + __uint(max_entries, 128); + __type(key, int); + __type(value, long); + } my_map SEC(".maps"); + + SEC("raw_tp/sys_exit") + int handle_sys_exit(struct pt_regs *ctx) + { + int zero = 0; + bpf_map_lookup_elem(&my_map, &zero); + return 0; + } + +**$ cat example3.bpf.c** + +:: + + #include <linux/ptrace.h> + #include <linux/bpf.h> + #include <bpf/bpf_helpers.h> + /* This header file is provided by the bpf_testmod module. */ + #include "bpf_testmod.h" + + int test_2_result = 0; + + /* bpf_Testmod.ko calls this function, passing a "4" + * and testmod_map->data. + */ + SEC("struct_ops/test_2") + void BPF_PROG(test_2, int a, int b) + { + test_2_result = a + b; + } + + SEC(".struct_ops") + struct bpf_testmod_ops testmod_map = { + .test_2 = (void *)test_2, + .data = 0x1, + }; + +This is example BPF application with three BPF programs and a mix of BPF +maps and global variables. Source code is split across three source code +files. + +**$ clang --target=bpf -g example1.bpf.c -o example1.bpf.o** + +**$ clang --target=bpf -g example2.bpf.c -o example2.bpf.o** + +**$ clang --target=bpf -g example3.bpf.c -o example3.bpf.o** + +**$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o example3.bpf.o** + +This set of commands compiles *example1.bpf.c*, *example2.bpf.c* and +*example3.bpf.c* individually and then statically links respective object +files into the final BPF ELF object file *example.bpf.o*. + +**$ bpftool gen skeleton example.bpf.o name example | tee example.skel.h** + +:: + + /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */ + + /* THIS FILE IS AUTOGENERATED! */ + #ifndef __EXAMPLE_SKEL_H__ + #define __EXAMPLE_SKEL_H__ + + #include <stdlib.h> + #include <bpf/libbpf.h> + + struct example { + struct bpf_object_skeleton *skeleton; + struct bpf_object *obj; + struct { + struct bpf_map *rodata; + struct bpf_map *data; + struct bpf_map *bss; + struct bpf_map *my_map; + struct bpf_map *testmod_map; + } maps; + struct { + struct example__testmod_map__bpf_testmod_ops { + const struct bpf_program *test_1; + const struct bpf_program *test_2; + int data; + } *testmod_map; + } struct_ops; + struct { + struct bpf_program *handle_sys_enter; + struct bpf_program *handle_sys_exit; + } progs; + struct { + struct bpf_link *handle_sys_enter; + struct bpf_link *handle_sys_exit; + } links; + struct example__bss { + struct { + int x; + } data; + int test_2_result; + } *bss; + struct example__data { + _Bool global_flag; + long int handle_sys_enter_my_static_var; + } *data; + struct example__rodata { + int param1; + } *rodata; + }; + + static void example__destroy(struct example *obj); + static inline struct example *example__open_opts( + const struct bpf_object_open_opts *opts); + static inline struct example *example__open(); + static inline int example__load(struct example *obj); + static inline struct example *example__open_and_load(); + static inline int example__attach(struct example *obj); + static inline void example__detach(struct example *obj); + + #endif /* __EXAMPLE_SKEL_H__ */ + +**$ cat example.c** + +:: + + #include "example.skel.h" + + int main() + { + struct example *skel; + int err = 0; + + skel = example__open(); + if (!skel) + goto cleanup; + + skel->rodata->param1 = 128; + + /* Change the value through the pointer of shadow type */ + skel->struct_ops.testmod_map->data = 13; + + err = example__load(skel); + if (err) + goto cleanup; + + /* The result of the function test_2() */ + printf("test_2_result: %d\n", skel->bss->test_2_result); + + err = example__attach(skel); + if (err) + goto cleanup; + + /* all libbpf APIs are usable */ + printf("my_map name: %s\n", bpf_map__name(skel->maps.my_map)); + printf("sys_enter prog FD: %d\n", + bpf_program__fd(skel->progs.handle_sys_enter)); + + /* detach and re-attach sys_exit program */ + bpf_link__destroy(skel->links.handle_sys_exit); + skel->links.handle_sys_exit = + bpf_program__attach(skel->progs.handle_sys_exit); + + printf("my_static_var: %ld\n", + skel->bss->handle_sys_enter_my_static_var); + + cleanup: + example__destroy(skel); + return err; + } + +**# ./example** + +:: + + test_2_result: 17 + my_map name: my_map + sys_enter prog FD: 8 + my_static_var: 7 + +This is a stripped-out version of skeleton generated for above example code. + +min_core_btf +------------ + +**$ bpftool btf dump file 5.4.0-example.btf format raw** + +:: + + [1] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none) + [2] CONST '(anon)' type_id=1 + [3] VOLATILE '(anon)' type_id=1 + [4] ARRAY '(anon)' type_id=1 index_type_id=21 nr_elems=2 + [5] PTR '(anon)' type_id=8 + [6] CONST '(anon)' type_id=5 + [7] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=(none) + [8] CONST '(anon)' type_id=7 + [9] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none) + <long output> + +**$ bpftool btf dump file one.bpf.o format raw** + +:: + + [1] PTR '(anon)' type_id=2 + [2] STRUCT 'trace_event_raw_sys_enter' size=64 vlen=4 + 'ent' type_id=3 bits_offset=0 + 'id' type_id=7 bits_offset=64 + 'args' type_id=9 bits_offset=128 + '__data' type_id=12 bits_offset=512 + [3] STRUCT 'trace_entry' size=8 vlen=4 + 'type' type_id=4 bits_offset=0 + 'flags' type_id=5 bits_offset=16 + 'preempt_count' type_id=5 bits_offset=24 + <long output> + +**$ bpftool gen min_core_btf 5.4.0-example.btf 5.4.0-smaller.btf one.bpf.o** + +**$ bpftool btf dump file 5.4.0-smaller.btf format raw** + +:: + + [1] TYPEDEF 'pid_t' type_id=6 + [2] STRUCT 'trace_event_raw_sys_enter' size=64 vlen=1 + 'args' type_id=4 bits_offset=128 + [3] STRUCT 'task_struct' size=9216 vlen=2 + 'pid' type_id=1 bits_offset=17920 + 'real_parent' type_id=7 bits_offset=18048 + [4] ARRAY '(anon)' type_id=5 index_type_id=8 nr_elems=6 + [5] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none) + [6] TYPEDEF '__kernel_pid_t' type_id=8 + [7] PTR '(anon)' type_id=3 + [8] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED + <end> + +Now, the "5.4.0-smaller.btf" file may be used by libbpf as an external BTF file +when loading the "one.bpf.o" object into the "5.4.0-example" kernel. Note that +the generated BTF file won't allow other eBPF objects to be loaded, just the +ones given to min_core_btf. + +:: + + LIBBPF_OPTS(bpf_object_open_opts, opts, .btf_custom_path = "5.4.0-smaller.btf"); + struct bpf_object *obj; + + obj = bpf_object__open_file("one.bpf.o", &opts); + + ... |