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author | 2021-03-18 12:40:33 -0700 | |
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committer | 2021-03-18 16:14:23 -0700 | |
commit | d80b2fcbe0a023619e0fc73112f2a02c2662f6ab (patch) | |
tree | 5a232c9c067b8af8ef6a1789d09d55a64f4a15cc /tools/bpf/bpftool/Documentation/bpftool-gen.rst | |
parent | bpftool: Add ability to specify custom skeleton object name (diff) | |
download | wireguard-linux-d80b2fcbe0a023619e0fc73112f2a02c2662f6ab.tar.xz wireguard-linux-d80b2fcbe0a023619e0fc73112f2a02c2662f6ab.zip |
bpftool: Add `gen object` command to perform BPF static linking
Add `bpftool gen object <output-file> <input_file>...` command to statically
link multiple BPF ELF object files into a single output BPF ELF object file.
This patch also updates bash completions and man page. Man page gets a short
section on `gen object` command, but also updates the skeleton example to show
off workflow for BPF application with two .bpf.c files, compiled individually
with Clang, then resulting object files are linked together with `gen object`,
and then final object file is used to generate usable BPF skeleton. This
should help new users understand realistic workflow w.r.t. compiling
mutli-file BPF application.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-10-andrii@kernel.org
Diffstat (limited to 'tools/bpf/bpftool/Documentation/bpftool-gen.rst')
-rw-r--r-- | tools/bpf/bpftool/Documentation/bpftool-gen.rst | 65 |
1 files changed, 51 insertions, 14 deletions
diff --git a/tools/bpf/bpftool/Documentation/bpftool-gen.rst b/tools/bpf/bpftool/Documentation/bpftool-gen.rst index d4e7338e22e7..7cd6681137f3 100644 --- a/tools/bpf/bpftool/Documentation/bpftool-gen.rst +++ b/tools/bpf/bpftool/Documentation/bpftool-gen.rst @@ -14,16 +14,37 @@ SYNOPSIS *OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] } - *COMMAND* := { **skeleton** | **help** } + *COMMAND* := { **object** | **skeleton** | **help** } GEN COMMANDS ============= +| **bpftool** **gen object** *OUTPUT_FILE* *INPUT_FILE* [*INPUT_FILE*...] | **bpftool** **gen skeleton** *FILE* [**name** *OBJECT_NAME*] | **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*. @@ -133,26 +154,19 @@ OPTIONS EXAMPLES ======== -**$ cat example.c** +**$ cat example1.bpf.c** :: #include <stdbool.h> #include <linux/ptrace.h> #include <linux/bpf.h> - #include "bpf_helpers.h" + #include <bpf/bpf_helpers.h> const volatile int param1 = 42; bool global_flag = true; struct { int x; } data = {}; - 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_enter") int handle_sys_enter(struct pt_regs *ctx) { @@ -164,6 +178,21 @@ EXAMPLES 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) { @@ -173,9 +202,17 @@ EXAMPLES } This is example BPF application with two BPF programs and a mix of BPF maps -and global variables. +and global variables. Source code is split across two source code files. -**$ bpftool gen skeleton example.o** +**$ clang -target bpf -g example1.bpf.c -o example1.bpf.o** +**$ clang -target bpf -g example2.bpf.c -o example2.bpf.o** +**$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o** + +This set of commands compiles *example1.bpf.c* and *example2.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** :: @@ -230,7 +267,7 @@ and global variables. #endif /* __EXAMPLE_SKEL_H__ */ -**$ cat example_user.c** +**$ cat example.c** :: @@ -273,7 +310,7 @@ and global variables. return err; } -**# ./example_user** +**# ./example** :: |