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author | Andrii Nakryiko <andrii@kernel.org> | 2022-05-09 03:41:46 +0300 |
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committer | Daniel Borkmann <daniel@iogearbox.net> | 2022-05-09 18:15:32 +0300 |
commit | f760d0537925e2973ed3adc2e590aa2968d0e8dc (patch) | |
tree | a19c4f25b7f75e27bf680927ff6e28efe5f1f60b /tools/lib | |
parent | 785c3342cf6c520250258d8d7bc0cae1d4461dc8 (diff) | |
download | linux-f760d0537925e2973ed3adc2e590aa2968d0e8dc.tar.xz |
libbpf: Provide barrier() and barrier_var() in bpf_helpers.h
Add barrier() and barrier_var() macros into bpf_helpers.h to be used by
end users. While a bit advanced and specialized instruments, they are
sometimes indispensable. Instead of requiring each user to figure out
exact asm volatile incantations for themselves, provide them from
bpf_helpers.h.
Also remove conflicting definitions from selftests. Some tests rely on
barrier_var() definition being nothing, those will still work as libbpf
does the #ifndef/#endif guarding for barrier() and barrier_var(),
allowing users to redefine them, if necessary.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220509004148.1801791-8-andrii@kernel.org
Diffstat (limited to 'tools/lib')
-rw-r--r-- | tools/lib/bpf/bpf_helpers.h | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h index bbae9a057bc8..fb04eaf367f1 100644 --- a/tools/lib/bpf/bpf_helpers.h +++ b/tools/lib/bpf/bpf_helpers.h @@ -76,6 +76,30 @@ #endif /* + * Compiler (optimization) barrier. + */ +#ifndef barrier +#define barrier() asm volatile("" ::: "memory") +#endif + +/* Variable-specific compiler (optimization) barrier. It's a no-op which makes + * compiler believe that there is some black box modification of a given + * variable and thus prevents compiler from making extra assumption about its + * value and potential simplifications and optimizations on this variable. + * + * E.g., compiler might often delay or even omit 32-bit to 64-bit casting of + * a variable, making some code patterns unverifiable. Putting barrier_var() + * in place will ensure that cast is performed before the barrier_var() + * invocation, because compiler has to pessimistically assume that embedded + * asm section might perform some extra operations on that variable. + * + * This is a variable-specific variant of more global barrier(). + */ +#ifndef barrier_var +#define barrier_var(var) asm volatile("" : "=r"(var) : "0"(var)) +#endif + +/* * Helper macro to throw a compilation error if __bpf_unreachable() gets * built into the resulting code. This works given BPF back end does not * implement __builtin_trap(). This is useful to assert that certain paths |