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. arena_spin_lock_slowpath() uses two macros that produce values and ignores the results. Add (void) cast 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, 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@xxxxxxxxxxxxx> --- tools/testing/selftests/bpf/progs/bpf_arena_spin_lock.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/bpf/progs/bpf_arena_spin_lock.h b/tools/testing/selftests/bpf/progs/bpf_arena_spin_lock.h index d67466c1ff77..f90531cf3ee5 100644 --- a/tools/testing/selftests/bpf/progs/bpf_arena_spin_lock.h +++ b/tools/testing/selftests/bpf/progs/bpf_arena_spin_lock.h @@ -302,7 +302,7 @@ int arena_spin_lock_slowpath(arena_spinlock_t __arena __arg_arena *lock, u32 val * barriers. */ if (val & _Q_LOCKED_MASK) - smp_cond_load_acquire_label(&lock->locked, !VAL, release_err); + (void)smp_cond_load_acquire_label(&lock->locked, !VAL, release_err); /* * take ownership and clear the pending bit. @@ -380,7 +380,7 @@ int arena_spin_lock_slowpath(arena_spinlock_t __arena __arg_arena *lock, u32 val /* Link @node into the waitqueue. */ WRITE_ONCE(prev->next, node); - arch_mcs_spin_lock_contended_label(&node->locked, release_node_err); + (void)arch_mcs_spin_lock_contended_label(&node->locked, release_node_err); /* * While waiting for the MCS lock, the next pointer may have -- 2.50.1
