[PATCH v5 0/6] Add support for LoongArch32

[mengqinggang]

在 2026/3/4 09:52, mengqinggang 写道:
>
> 在 2026/3/4 00:33, Xi Ruoyao 写道:
>> On Tue, 2026-03-03 at 19:28 +0800, mengqinggang wrote:
>>> 在 2026/3/3 18:11, Xi Ruoyao 写道:
>>>> On Tue, 2026-03-03 at 17:54 +0800, mengqinggang wrote:
>>>>> LoongArch64 gcc generates call memset to fully zero-filling the 
>>>>> struct.
>>>>> But LoongArch32 gcc not generate call memset.
>>>>> Maybe we can fix LoongArch32 gcc to resolve this problem.
>>>> This is not a compiler bug so there's nothing to be fixed in the
>>>> compiler.  In C using = {...} to initialize a struct with automatic
>>>> storage duration will leave the padding bits unspecified, unless the
>>>> initializer is empty.
>>>>
>>>> See https://gcc.gnu.org/PR104607 which has been resolved as invalid
>>>> years ago.
>>> According to what you said, loongarch64 gcc should not generate call
>>> memset assembly code?
>> I don't think it should.  This seems a missed-optimization on almost all
>> GCC ports (GCC r16-7721 actually emits the memset for LA32...)
>>
> Only loongarch64 gcc generate call memset for the following code.
>
>   1 #include <errno.h>
>   2 #include <fcntl.h>
>   3 #include <limits.h>
>   4 #include <sys/pidfd.h>
>   5 #include <sys/wait.h>
>   6 #include <stdlib.h>
>   7 #include <stdio.h>
>   8 #include <unistd.h>
>   9
>  10 static pid_t ppid;
>  11 static uid_t puid;
>  12
>  13 int
>  14 main (void)
>  15 {
>  16   ppid = getpid ();
>  17   puid = getuid ();
>  18   pid_t pid = fork ();
>  19   if (pid != 0)
>  20   {
>  21     int pidfd = pidfd_open (pid, 0);
>  22     printf("pidfd %d\n", pidfd);
>  23     {
>  24       siginfo_t info =
>  25         {
>  26           .si_signo = SIGUSR2,
>  27           .si_errno = EAGAIN,
>  28           .si_code = -10,
>  29           .si_pid = ppid,
>  30           .si_uid = puid
>  31         };
>  32       int r = pidfd_send_signal (pidfd, SIGUSR2, &info, 0);
>  33       printf("pidfd r = %d\n", r);
>  34     }
>  35   }
>  36   return 0;
>  37 }
>
If wordsize is 64, there is an int __pad0.
Maybe this difference causes the loongarch64 gcc to generate call memset,
while the loongarch32 gcc does not.

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
  50
  51     union
  52       {
  53         int _pad[__SI_PAD_SIZE];
  54
  55          /* kill().  */
  56         struct
  57           {
  58             __pid_t si_pid;     /* Sending process ID.  */
  59             __uid_t si_uid;     /* Real user ID of sending 
process.  */
  60           } _kill;