Re: [PATCH bpf-next v2 17/23] selftests/bpf: Add tests for stack argument validation

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Unconditional use of the 'r11' register in inline assembly will cause selftest build failures on older Clang compilers.
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commit 6f66b8fd81d82b7d1f5f683d16976b8d486d440b
Author: Yonghong Song <yonghong.song@linux.dev>

selftests/bpf: Add tests for stack argument validation

This commit adds negative tests to verify that kfuncs properly reject large
structs passed as stack arguments. It also adds tests to ensure the verifier
rejects invalid uses of the r11 register for stack arguments.

> diff --git a/tools/testing/selftests/bpf/progs/stack_arg_fail.c b/tools/testing/selftests/bpf/progs/stack_arg_fail.c
> new file mode 100644
> index 0000000000000..c6db302549cbd
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/stack_arg_fail.c

[ ... ]

> +#else
> +
> +SEC("tc")
> +__description("stack_arg_fail: not supported, dummy test")
> +__success
> +int test_stack_arg_big(struct __sk_buff *skb)
> +{
> +	return 0;
> +}
> +
> +#endif
> +
> +SEC("socket")
> +__description("r11 in ALU instruction")
> +__failure __msg("R11 is invalid")
> +__naked void r11_alu_reject(void)
> +{
> +	asm volatile (
> +	"r11 += 1;"

Could these inline assembly blocks using r11 cause build failures on older
Clang compilers?

The r11 register is a relatively new addition to the BPF ISA and LLVM backend.
Because these naked assembly functions are placed outside of the
__BPF_FEATURE_STACK_ARGUMENT guard, compiling this file with an older
toolchain might result in fatal assembler errors regarding an invalid operand.

Would it be safer to move these r11 tests inside the feature guard to
maintain selftest compatibility across toolchains?

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20260507212942.1122000-1-yonghong.song@linux.dev?part=17