[Sanitizer] Fix the implementation of internal_fstat on LoongArch

[tangyouling]

Summary

If pathname is an empty string and the AT_EMPTY_PATH flag is specified in flags,
statx pathname argument is of type const char *restrict, so it should be ""
instead of 0.

[tangyouling]

#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <sys/stat.h>
#include <linux/stat.h>
#include <linux/fcntl.h>

int main(int argc, char **argv)
{
        int fd, ret;
        struct statx bufx;

        fd = open(*argv, O_RDONLY);
        if (fd < 0)
                printf("open %s failed\n", *argv);

        ret = syscall(__NR_statx ,fd, 0, AT_EMPTY_PATH, STATX_BASIC_STATS, (void *)&bufx);
        if (ret < 0)
                printf("statx(%s) failed, ret %d\n", *argv, ret);

        printf("statx(%s) successed, ret %d\n", *argv, ret);

        close(fd);

        return 0;
}

$ gcc test-statx.c
$ ./a.out a.out 
statx(./a.out) fail, ret -1

#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <sys/stat.h>
#include <linux/stat.h>
#include <linux/fcntl.h>

int main(int argc, char **argv)
{
        int fd, ret;
        struct statx bufx;

        fd = open(*argv, O_RDONLY);
        if (fd < 0)
                printf("open %s failed\n", *argv);

        ret = syscall(__NR_statx ,fd, "", AT_EMPTY_PATH, STATX_BASIC_STATS, (void *)&bufx);
        if (ret < 0)
                printf("statx(%s) failed, ret %d\n", *argv, ret);

        printf("statx(%s) successed, ret %d\n", *argv, ret);

        close(fd);

        return 0;
}

$ gcc test-statx.c
$ ./a.out 
statx(./a.out) successed, ret 0

[xry111]

LGTM, thanks for fixing my stupid error!

Not sure how I wrote "0" here in the first place :(.

[xen0n]

we all gotta read manpages real hard

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

 #if SANITIZER_MIPS64
   // For mips64, fstat syscall fills buffer in the format of kernel_stat
   struct kernel_stat kbuf;
   int res = internal_syscall(SYSCALL(fstat), fd, &kbuf);
   kernel_stat_to_stat(&kbuf, (struct stat *)buf);
   return res;
 #      elif SANITIZER_LINUX && defined(__loongarch__)
   struct statx bufx;
-  int res = internal_syscall(SYSCALL(statx), fd, 0, AT_EMPTY_PATH,
+  int res = internal_syscall(SYSCALL(statx), fd, "", AT_EMPTY_PATH,
                              STATX_BASIC_STATS, (uptr)&bufx);
   statx_to_stat(&bufx, (struct stat *)buf);
   return res;
 #      else
   return internal_syscall(SYSCALL(fstat), fd, (uptr)buf);
 #      endif
 #else
   struct stat64 buf64;