[PATCH v2] linux: Enforce zero fill of siginfo_t

[mengqinggang]

Gcc zero-initialize the whole struct like this:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124356

Struct siginfo has an extra "int __pad0" if __WORDSIZE == 64.
sysdeps/unix/sysv/linux/bits/types/siginfo_t.h
  36 typedef struct
  37   {
  38     int si_signo;               /* Signal number.  */
  39 #if __SI_ERRNO_THEN_CODE
  40     int si_errno;               /* If non-zero, an errno value 
associated with
  41                                    this signal, as defined in 
<errno.h>.  */
  42     int si_code;                /* Signal code.  */
  43 #else
  44     int si_code;
  45     int si_errno;
  46 #endif
  47 #if __WORDSIZE == 64
  48     int __pad0;                 /* Explicit padding.  */
  49 #endif

This initialization code causes gcc to zero the whole struct only on 
64-bit targets.
213     siginfo_t info =
214       {
215         .si_signo = SIGUSR2,
216         .si_errno = EAGAIN,
217         .si_code = -10,
218         .si_pid = ppid,
219         .si_uid = puid
220       };


So I think this patch is necessary for 32-bit targets.


在 2026/4/21 14:25, Florian Weimer 写道:
> * Adhemerval Zanella:
>
>> The glibc siginfo struct is larger than the kABI one, and the kernel
>> enforces that for an unknown si_code, all the extra bytes should be 0
>> (post_copy_siginfo_from_user).
> I still think the explanation of this change is wrong (I think it's that
> designated initializers with unions do not necessary zero-initialize
> inactive members), but the code change itself is correct.
>
> Thanks,
> Florian