Chen Li <che...@uniontech.com> 于2021年3月8日周一 下午2:35写道：
>
>
> 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.
>
It only has this problem on mips64.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=983769
> 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.
>
> Maybe sparc also suffers from this problem, but I have no machine to
> verify.
> ---
> .../testsuite/27_io/filesystem/operations/last_write_time.cc | 2 ++
> .../experimental/filesystem/operations/last_write_time.cc | 2 ++
> 2 files changed, 4 insertions(+)
>
> diff --git
> a/libstdc++-v3/testsuite/27_io/filesystem/operations/last_write_time.cc
> b/libstdc++-v3/testsuite/27_io/filesystem/operations/last_write_time.cc
> index 6ae64c482b6..72272d4e781 100644
> --- a/libstdc++-v3/testsuite/27_io/filesystem/operations/last_write_time.cc
> +++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/last_write_time.cc
> @@ -200,11 +200,13 @@ test02()
> VERIFY( approx_equal(last_write_time(f.path), time) );
>
> ec = bad_ec;
> + #ifndef __mips__
> // A time before than the epoch
> time -= chrono::milliseconds(1000 * 60 * 20 + 15);
> last_write_time(f.path, time, ec);
> VERIFY( !ec );
> VERIFY( approx_equal(last_write_time(f.path), time) );
> + #endif
> }
>
> int
> diff --git
> a/libstdc++-v3/testsuite/experimental/filesystem/operations/last_write_time.cc
>
> b/libstdc++-v3/testsuite/experimental/filesystem/operations/last_write_time.cc
> index 536ab1f28f6..6fb490a6bc3 100644
> ---
> a/libstdc++-v3/testsuite/experimental/filesystem/operations/last_write_time.cc
> +++
> b/libstdc++-v3/testsuite/experimental/filesystem/operations/last_write_time.cc
> @@ -165,11 +165,13 @@ test02()
> VERIFY( !ec );
> VERIFY( approx_equal(last_write_time(f.path), time) );
>
> + #ifndef __mips__
> ec = bad_ec;
> time -= chrono::milliseconds(1000 * 60 * 10 + 15);
> last_write_time(f.path, time, ec);
> VERIFY( !ec );
> VERIFY( approx_equal(last_write_time(f.path), time) );
> + #endif
> }
>
> int
> --
> 2.30.0
>
>
>
--
YunQiang Su
