On 08/03/21 14:35 +0800, Chen Li wrote:
When execute libstdc++ testcases on mips, I notice that last_write_time
alawys failed, and the failed VERIFY is "VERIFY(
approx_equal(last_write_time(f.path), time) );" where testing time before
than epoch.
Below is the minimal case:
```
// gcc a.c
int main()
{
struct timespec times[2] = {{1, UTIME_OMIT}, {-1201, 985000000}};
utimensat(AT_FDCWD, "test", times, 0);
}
```
$ touch test && gcc a.c && ./a.out && stat test
File: test
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 805h/2053d Inode: 1056841 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1000/ deepin) Gid: ( 1000/ deepin)
Access: 2021-03-08 13:52:55.966354501 +0800
Modify: 2106-02-07 14:08:15.985000000 +0800
Change: 2021-03-08 13:52:56.907782193 +0800
Birth: -
Undoubtedly, mtime's type is unsigned somewhere on mips.
After debuging kernel, it turns out that mtime is always -1201 in
ext4_setattr, cp_new_stat, newlstat and etc, so the problem should not
occur in kernel space.
go back to user space via copy_to_user, I finally found mips used
"unsigned int st_mtime_sec;" in struct kernel_stat, which is used to
receive -1201 from kernel.
I can't reproduce this on a mips64 machine:
jwakely@erpro8-fsf2:~$ uname -a
Linux erpro8-fsf2 4.1.4 #1 SMP PREEMPT Mon Aug 3 14:22:54 PDT 2015 mips64
GNU/Linux
jwakely@erpro8-fsf2:~$ apt list libc6
Listing... Done
libc6/oldstable,now 2.19-18+deb8u10 mipsel [installed]
jwakely@erpro8-fsf2:~$ touch test && ./a.out && TZ= stat test
File: ‘test’
Size: 0 Blocks: 0 IO Block: 131072 regular empty file
Device: 21h/33d Inode: 36596524 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1049/ jwakely) Gid: ( 1049/ jwakely)
Access: 2021-03-08 10:52:06.855991946 +0000
Modify: 1969-12-31 23:39:59.985000000 +0000
Change: 2021-03-08 10:52:06.859992051 +0000
Birth: -
This is an ext4 filesystem.
Do I need to compile a 64-bit executable?
In any case, shouldn't this be fixed in glibc to return EINVAL instead
of setting a bogus time? That would make the std::filesystem library
report an error.
Maybe sparc also suffers from this problem, but I have no machine to
verify.
Your test case works correctly for me on sparc-linux (both 32-bit and
64-bit on ext4 and xfs filesystems):
$ uname -a
Linux gcc202 5.10.0-4-sparc64-smp #1 SMP Debian 5.10.19-1 (2021-03-02) sparc64
GNU/Linux
$ apt list libc6
Listing... Done
libc6/unstable,now 2.31-4 sparc64 [installed]
$ ./a.out
$ TZ= stat test
File: test
Size: 0 Blocks: 0 IO Block: 8192 regular empty file
Device: fd01h/64769d Inode: 657291843 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1049/ jwakely) Gid: ( 1049/ jwakely)
Access: 2021-03-08 10:25:43.593819539 +0000
Modify: 1969-12-31 23:39:59.985000000 +0000
Change: 2021-03-08 10:34:13.711287778 +0000
Birth: 2021-03-08 10:24:27.106598699 +0000
