Re: [PATCH bpf-next 3/3] selftests/bpf: Enable some of the blocked cpuv4 instruction tests for bpf-gcc

[Eduard Zingerman <eddyz87@gmail.com>]

On Fri, 2026-08-21 at 13:13 -0700, Vineet Gupta wrote:
> A bunch of tests are gated behind clang only __clang_major__ and thus
> fail to build under BPF_GCC. What's worse is, before the prev patch they
> were also declared as passing/OK.
> 
> This need not be because (a) bpf-gcc does support the feature in codegen
> and (b) also advertises correctly with feature support preprocessor macros:
> 
>   __BPF_FEATURE_BSWAP, __BPF_FEATURE_GOTOL, __BPF_FEATURE_LDSX,
>   __BPF_FEATURE_MOVSX, __BPF_FEATURE_SDIV_SMOD, __BPF_FEATURE_ST
> 
> So loosen up the gates to also add specific feature check.
> clang >=18 has to stay, despite it being true for so long: clang only
> defines __BPF_FEATURE_MOVSX and friends at -mcpu=v4, but assembles the
> inline asm at -mcpu=v3 too, and dropping it would remove these tests from
> the default test_progs flavour where they run today.

Huh, that's unfortunate.

> 
> Since bpf-gcc doesn't support addr_space_cast, wrap the corresponding
> tests under __BPF_FEATURE_ADDR_SPACE_CAST to skip under it.
> And also move the map under that guard so that a bpf-gcc object does not
> declare an arena map that no program in it references.
> 
> Recovered under BPF_GCC (programs per object, was 1 dummy each):
> 
>   verifier_sdiv    80
>   verifier_movsx   17
>   verifier_ldsx    14   (20 under clang; 5 arena tests,
>                        kfunc_root and the arena map stay clang-only)
>   verifier_bswap   13
> 
> CAN_USE_GOTOL and CAN_USE_BPF_ST only gate parts of a file, so those were
> not dummies to begin with:
> 
>   compute_live_registers        17 -> 19  (21 under clang)
>   verifier_gotol                 1 -> 2
>   verifier_iterating_callbacks  34 -> 35
> 
> The clang builds are unchanged: verifier_ldsx still emits 20 programs under
> the cpuv4 flavour.
> 
> One thing left alone: verifier_load_acquire.c and verifier_store_release.c
> stay clang-only, and their gates are correct as gas doesn't implement
> those (experimental -mxbpf not implemented at all). FWIW LLVM groups
> those under -mcpu=v4 and defines __BPF_FEATURE_LOAD_ACQ_STORE_REL there.
> 
> Signed-off-by: Vineet Gupta <vineet.gupta@linux.dev>
> ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

I'll wait for v2 and apply.

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