On Thu, May 8, 2025 at 12:21 PM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> wrote:
>
> On Thu, 2025-05-08 at 11:38 -0700, Alexei Starovoitov wrote:
> > On Thu, May 8, 2025 at 4:38 AM Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> > wrote:
> > >
> > > clang-21 complains about unused expressions in a few progs.
> > > Fix by explicitly casting the respective expressions to void.
> >
> > ...
> > > 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);
> >
> > Hmm. I'm on clang-21 too and I don't see them.
> > What warnings do you see ?
>
> In file included from progs/arena_spin_lock.c:7:
> progs/bpf_arena_spin_lock.h:305:1756: error: expression result unused
> [-Werror,-Wunused-value]
> 305 | ({ typeof(_Generic((*&lock->locked), char: (char)0, unsigned
> char : (unsigned char)0, signed char : (signed char)0, unsigned short :
> (unsigned short)0, signed short : (signed short)0, unsigned int :
> (unsigned int)0, signed int : (signed int)0, unsigned long : (unsigned
> long)0, signed long : (signed long)0, unsigned long long : (unsigned
> long long)0, signed long long : (signed long long)0, default:
> (typeof(*&lock->locked))0)) __val = ({ typeof(&lock->locked) __ptr =
> (&lock->locked); typeof(_Generic((*(&lock->locked)), char: (char)0,
> unsigned char : (unsigned char)0, signed char : (signed char)0,
> unsigned short : (unsigned short)0, signed short : (signed short)0,
> unsigned int : (unsigned int)0, signed int : (signed int)0, unsigned
> long : (unsigned long)0, signed long : (signed long)0, unsigned long
> long : (unsigned long long)0, signed long long : (signed long long)0,
> default: (typeof(*(&lock->locked)))0)) VAL; for (;;) { VAL =
> (typeof(_Generic((*(&lock->locked)), char: (char)0, unsigned char :
> (unsigned char)0, signed char : (signed char)0, unsigned short :
> (unsigned short)0, signed short : (signed short)0, unsigned int :
> (unsigned int)0, signed int : (signed int)0, unsigned long : (unsigned
> long)0, signed long : (signed long)0, unsigned long long : (unsigned
> long long)0, signed long long : (signed long long)0, default:
> (typeof(*(&lock->locked)))0)))(*(volatile typeof(*__ptr) *)&(*__ptr));
> if (!VAL) break; ({ __label__ l_break, l_continue; asm volatile
> goto("may_goto %l[l_break]" :::: l_break); goto l_continue; l_break:
> goto release_err; l_continue:; }); ({}); } (typeof(*(&lock-
> >locked)))VAL; }); ({ ({ if (!CONFIG_X86_64) ({ unsigned long __val;
> __sync_fetch_and_add(&__val, 0); }); else asm volatile("" :::
> "memory"); }); }); (typeof(*(&lock->locked)))__val; });
> |
> ^ ~~~~~
> 1 error generated.
hmm. The error is impossible to read.
Kumar,
Do you see a way to silence it differently ?
Without adding (void)...
Things like:
- bpf_obj_new(..
+ (void)bpf_obj_new(..
are good to fix, and if we could annotate
bpf_obj_new_impl kfunc with __must_check we would have done it,
but
- arch_mcs_spin_lock...
+ (void)arch_mcs_spin_lock...
is odd.
> It started today.
> Here is the full compiler version:
>
> $ clang-21 --version
> Debian clang version 21.0.0 (++20250501112544+75d1cceb9486-
> 1~exp1~20250501112558.1422)
> Target: s390x-unknown-linux-gnu
> Thread model: posix
> InstalledDir: /usr/lib/llvm-21/bin
>
> Best regards,
> Ilya
