[sanitizer] Correct alignment of x32 __sanitizer_siginfo

[hjl.tools]

Summary

Since alignment of x32 siginfo_t is 8 bytes, not 4 bytes, use u64 in
sanitizer_siginfo_pad to align x32 sanitizer_siginfo to 8 bytes.

Fixes https://github.com/llvm/llvm-project/issues/62394

[MaskRay]

Thanks for the patch. If I read sysdeps/unix/sysv/linux/bits/types/siginfo_t.h and sysdeps/unix/sysv/linux/x86/bits/siginfo-arch.h correct, the x32 ABI does use 8-byte alignment for siginfo_t.

compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h

587

If x32 is the canonical spelling

[MaskRay]

D142117 changed(fixed?) the alignment to 4 for x86-32. Any idea why COMPILER_CHECK(alignof(siginfo_t) == alignof(__sanitizer_siginfo)); did not fail for x86-32?

[hjl.tools]

compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h

587

If x32 is the canonical spelling

Will update.

[hjl.tools]

In D149309#4300794, @MaskRay wrote:

D142117 changed(fixed?) the alignment to 4 for x86-32. Any idea why COMPILER_CHECK(alignof(siginfo_t) == alignof(__sanitizer_siginfo)); did not fail for x86-32?

x86-32 siginfo_t is 4-byte aligned.

compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h

 #elif SANITIZER_LINUX
 struct __sanitizer_sigset_t {
   // The size is determined by looking at sizeof of real sigset_t on linux.
   uptr val[128 / sizeof(uptr)];
 };
 #endif
 
 struct __sanitizer_siginfo_pad {
+#if SANITIZER_X32
+  // x32 siginfo_t is aligned to 8 bytes.
+  u64 pad[128 / sizeof(u64)];
+#else
   // Require uptr, because siginfo_t is always pointer-size aligned on Linux.
   uptr pad[128 / sizeof(uptr)];
+#endif
 };
 
 #if SANITIZER_LINUX
 # define SANITIZER_HAS_SIGINFO 1
 union __sanitizer_siginfo {
   struct {
     int si_signo;
 # if SANITIZER_MIPS