Teach libarena's BPF atomic primitives to use compiler builtins for load-acquire and store-release when Clang advertises __BPF_FEATURE_LOAD_ACQ_STORE_REL. Older compilers continue to use the existing barrier-based fallback. Notably, as BPF programs begin running on arm64, it is better to use the more appropriate variants since we can no longer rely on x86 TSO ordering. Commit 880442305a39 ("bpf: Introduce load-acquire and store-release instructions") introduced support, hence kernels from 6.15 onwards are needed when compiling with compilers supporting these instructions. We have relatively recent kernel version requirements in libarena anyway, and have not cut first release, hence declare such a dependency. Signed-off-by: Puranjay Mohan --- Changelog: v1: https://lore.kernel.org/bpf/20260721185705.1365329-1-memxor@gmail.com/ Changes in v2: - Use __BPF_FEATURE_LOAD_ACQ_STORE_REL directly for guard. - Use __unqual_typeof --- .../bpf/libarena/include/bpf_atomic.h | 20 +++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/tools/testing/selftests/bpf/libarena/include/bpf_atomic.h b/tools/testing/selftests/bpf/libarena/include/bpf_atomic.h index b7b2304319295..4558fa26911f6 100644 --- a/tools/testing/selftests/bpf/libarena/include/bpf_atomic.h +++ b/tools/testing/selftests/bpf/libarena/include/bpf_atomic.h @@ -86,6 +86,25 @@ extern bool CONFIG_X86_64 __kconfig __weak; /* Control dependency provides LOAD->STORE, provide LOAD->LOAD */ #define smp_acquire__after_ctrl_dep() ({ smp_rmb(); }) +#if defined(__BPF_FEATURE_LOAD_ACQ_STORE_REL) +/* + * Clang advertises this feature when it can lower acquire/release atomic + * builtins to BPF_LOAD_ACQ/BPF_STORE_REL. Older compilers keep using the + * barrier-based fallback below. The generated instructions require kernel + * verifier/JIT support added in Linux 6.15; compile for an older BPF CPU to + * keep using the fallback when targeting older kernels. + */ +#define smp_load_acquire(p) \ + ({ \ + __unqual_typeof(*(p)) ___p1 = __atomic_load_n((p), __ATOMIC_ACQUIRE); \ + (typeof(*(p)))___p1; \ + }) + +#define smp_store_release(p, val) \ + do { \ + __atomic_store_n((p), (val), __ATOMIC_RELEASE); \ + } while (0) +#else #define smp_load_acquire(p) \ ({ \ __unqual_typeof(*(p)) __v = READ_ONCE(*(p)); \ @@ -102,6 +121,7 @@ extern bool CONFIG_X86_64 __kconfig __weak; barrier(); \ WRITE_ONCE(*(p), val); \ }) +#endif #define smp_cond_load_relaxed_label(p, cond_expr, label) \ ({ \ base-commit: a23a71823352e2d792dcaae25f1ebb744acbfc0b -- 2.53.0-Meta