Re: [PATCH bpf-next v4 1/1] selftests/bpf: Fix "expression result unused" warnings with icecc

[Yonghong Song <yonghong.song@linux.dev>]

On 8/28/25 7:53 PM, Ilya Leoshkevich wrote:
> icecc is a compiler wrapper that distributes compile jobs over a build
> farm [1]. It works by sending toolchain binaries and preprocessed
> source code to remote machines.
>
> Unfortunately using it with BPF selftests causes build failures due to
> a clang bug [2]. The problem is that clang suppresses the
> -Wunused-value warning if the unused expression comes from a macro
> expansion. Since icecc compiles preprocessed source code, this
> information is not available. This leads to -Wunused-value false
> positives.
>
> obj_new_no_struct() and obj_new_acq() use the bpf_obj_new() macro and
> discard the result. arena_spin_lock_slowpath() uses two macros that
> produce values and ignores the results. Add (void) casts to explicitly
> indicate that this is intentional and suppress the warning.
>
> An alternative solution is to change the macros to not produce values.
> This would work today for the arena_spin_lock_slowpath() issue, but in
> the future there may appear users who need them. Another potential
> solution is to replace these macros with functions. Unfortunately this
> would not work, because these macros work with unknown types and
> control flow.
>
> [1] https://github.com/icecc/icecream
> [2] https://github.com/llvm/llvm-project/issues/142614
>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>

Acked-by: Yonghong Song <yonghong.song@linux.dev>