selftests/bpf: Adjust fexit_bpf2bpf ctx layout for llvm23 true signature

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test_pkt_access_subprog2() is defined in C as

  int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)

but llvm optimizes away the unused 'int val' argument. Before llvm23 the
BTF signature did not match the optimized assembly, so the verifier set
attach_func_proto to NULL and fell back to MAX_BPF_FUNC_REG_ARGS (5) u64
arguments (see btf_ctx_access()). The fexit ctx struct therefore placed
the return value after args[5].

With llvm23 the 'true' signature

  int test_pkt_access_subprog2(volatile struct __sk_buff *skb)

is recorded in BTF, so nr_args becomes 1 and the return value moves to
the slot right after args[1]. Select the matching args_subprog2 layout
based on __clang_major__ so the test works with both old and new llvm.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260609233412.2712178-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

...

This commit is contained in:

Yonghong Song 2026-06-09 16:34:12 -07:00 • committed by Alexei Starovoitov

parent be1d838b88

commit e775c522a4

1 changed files with 11 additions and 2 deletions

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tools/testing/selftests/bpf/progs/fexit_bpf2bpf.c

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