Many instances of -Wattribute-alias after LLVM commit 40da6920a0d71d49dfa2392b09153600b0759f5e

[nathanchance]

llvm/llvm-project@40da692

kernel/seccomp.c:2126:1: warning: alias and aliasee have different types 'long (unsigned int, unsigned int, void *)' and 'long (typeof (__builtin_choose_expr((__builtin_types_compatible_p(typeof ((unsigned int)0), typeof (0LL)) || __builtin_types_compatible_p(typeof ((unsigned int)0), typeof (0ULL))), 0LL, 0L)), typeof (__builtin_choose_expr((__builtin_types_compatible_p(typeof ((unsigned int)0), typeof (0LL)) || __builtin_types_compatible_p(typeof ((unsigned int)0), typeof (0ULL))), 0LL, 0L)), typeof (__builtin_choose_expr((__builtin_types_compatible_p(typeof ((void *)0), typeof (0LL)) || __builtin_types_compatible_p(typeof ((void *)0), typeof (0ULL))), 0LL, 0L)))' (aka 'long (long, long, long)') [-Wattribute-alias]
 2126 | SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags,
      | ^
include/linux/syscalls.h:227:36: note: expanded from macro 'SYSCALL_DEFINE3'
  227 | #define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, __VA_ARGS__)
      |                                    ^
include/linux/syscalls.h:236:2: note: expanded from macro 'SYSCALL_DEFINEx'
  236 |         __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
      |         ^
include/linux/syscalls.h:251:18: note: expanded from macro '__SYSCALL_DEFINEx'
  251 |                 __attribute__((alias(__stringify(__se_sys##name))));    \
      |                                ^
kernel/seccomp.c:2126:1: note: aliasee is declared here
include/linux/syscalls.h:227:36: note: expanded from macro 'SYSCALL_DEFINE3'
  227 | #define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, __VA_ARGS__)
      |                                    ^
include/linux/syscalls.h:236:2: note: expanded from macro 'SYSCALL_DEFINEx'
  236 |         __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
      |         ^
include/linux/syscalls.h:255:18: note: expanded from macro '__SYSCALL_DEFINEx'
  255 |         asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__))  \
      |                         ^
<scratch space>:59:1: note: expanded from here
   59 | __se_sys_seccomp
      | ^
1 warning generated.

We will need to match commit bee20031772a ("disable -Wattribute-alias warning for SYSCALL_DEFINEx()"). I will send a patch for this.

[nickdesaulniers]

We will need to match commit bee20031772a

After I reported this as GCC PR82435, a new
-Wno-attribute-alias

Does clang have that flag? Does clang need it?

[nathanchance]

Does clang have that flag? Does clang need it?

It seems like it?

clang -Wno-attribute-alias -c -o /dev/null -x c /dev/null

does not warn about an unknown flag. I assume that it gets it automatically from DiagGroup or something like that? Regardless, we don't need the explicit negative flag as long as _Pragma(clang diagnostic ignored -Wattribute-alias) works (which it does). I am running my patch through my full build tests before I send it, just to make sure it handles everything and there are no additional cases that need to be handled.

[nathanchance]

https://lore.kernel.org/20260515-syscall-disable-attribute-alias-for-clang-v1-1-9a9d95d41df6@kernel.org/