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| author | Jiri Olsa <jolsa@kernel.org> | 2022-09-03 16:11:54 +0300 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2022-09-16 23:23:20 +0300 |
| commit | ceea991a019c57a1fb0edd12a5f836a0fa431aee (patch) | |
| tree | a7f8c1564646e0e153392ddaf5369ae1135b9781 /include | |
| parent | 9440155ccb948f8e3ce5308907a2e7378799be60 (diff) | |
| download | linux-ceea991a019c57a1fb0edd12a5f836a0fa431aee.tar.xz | |
bpf: Move bpf_dispatcher function out of ftrace locations
The dispatcher function is attached/detached to trampoline by
dispatcher update function. At the same time it's available as
ftrace attachable function.
After discussion [1] the proposed solution is to use compiler
attributes to alter bpf_dispatcher_##name##_func function:
- remove it from being instrumented with __no_instrument_function__
attribute, so ftrace has no track of it
- but still generate 5 nop instructions with patchable_function_entry(5)
attribute, which are expected by bpf_arch_text_poke used by
dispatcher update function
Enabling HAVE_DYNAMIC_FTRACE_NO_PATCHABLE option for x86, so
__patchable_function_entries functions are not part of ftrace/mcount
locations.
Adding attributes to bpf_dispatcher_XXX function on x86_64 so it's
kept out of ftrace locations and has 5 byte nop generated at entry.
These attributes need to be arch specific as pointed out by Ilya
Leoshkevic in here [2].
The dispatcher image is generated only for x86_64 arch, so the
code can stay as is for other archs.
[1] https://lore.kernel.org/bpf/20220722110811.124515-1-jolsa@kernel.org/
[2] https://lore.kernel.org/bpf/969a14281a7791c334d476825863ee449964dd0c.camel@linux.ibm.com/
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/bpf/20220903131154.420467-3-jolsa@kernel.org
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/bpf.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 54178b9e9c3a..e0dbe0c0a17e 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -977,7 +977,14 @@ int arch_prepare_bpf_dispatcher(void *image, s64 *funcs, int num_funcs); }, \ } +#ifdef CONFIG_X86_64 +#define BPF_DISPATCHER_ATTRIBUTES __attribute__((patchable_function_entry(5))) +#else +#define BPF_DISPATCHER_ATTRIBUTES +#endif + #define DEFINE_BPF_DISPATCHER(name) \ + notrace BPF_DISPATCHER_ATTRIBUTES \ noinline __nocfi unsigned int bpf_dispatcher_##name##_func( \ const void *ctx, \ const struct bpf_insn *insnsi, \ |