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Re: libgo patch committed: Update to current version of Go library


On Fri, Feb 8, 2013 at 5:21 PM, Ian Lance Taylor <iant@google.com> wrote:
> On Fri, Feb 8, 2013 at 7:23 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
>> On Fri, Feb 8, 2013 at 4:02 PM, Ian Lance Taylor <iant@google.com> wrote:
>>
>>>>>> I did hit one new error that seems related:
>>>>>>
>>>>>> --- FAIL: TestChtimes (0.00 seconds)
>>>>>> os_test.go:681:         AccessTime didn't go backwards;
>>>>>> was={63495872497 0 47130825733376}, after={63495872497 0
>>>>>> 47130825733376}
>>>>>> os_test.go:685:         ModTime didn't go backwards; was={63495872497
>>>>>> 0 47130825733376}, after={63495872497 0 47130825733376}
>>>>>> FAIL
>>>>>> FAIL: os
>>>>>
>>>>> Something has gone wrong in the file
>>>>> libgo/go/syscall/libcall_linux_utimesnano.go.  The function in that
>>>>> file will try utimensat.  On your system that should return ENOSYS.
>>>>> In that case the function should convert the times and call utimes.
>>>>> The code looks OK to me but there may be something wrong with it.  It
>>>>> looks like the file times didn't change at all.
>>>>
>>>> From the strace -f, it looks that utimes is not called at all in
>>>> between two relevant stats:
>>>
>>> Strange.  What I would expect to happen is that the function in
>>> libcall_linux_utimesnano.go will call utimensat.  Since your system
>>> does not have that function, that will call the stub routine in
>>> libgo/runtime/go-nosys.c, which will return -1 with errno set to
>>> ENOSYS.  The code in libcall_linux_utimensnano.go will see the ENOSYS
>>> error and continue on to call utime.  Clearly something is going wrong
>>> in that sequence, but I don't know what.
>>
>> Somwhow expected, following "patch" makes test to pass:
>>
>> --cut here--
>> Index: go/syscall/libcall_linux_utimesnano.go
>> ===================================================================
>> --- go/syscall/libcall_linux_utimesnano.go      (revision 195879)
>> +++ go/syscall/libcall_linux_utimesnano.go      (working copy)
>> @@ -14,10 +14,10 @@
>>         if len(ts) != 2 {
>>                 return EINVAL
>>         }
>> -       err = utimensat(_AT_FDCWD, path,
>> (*[2]Timespec)(unsafe.Pointer(&ts[0])), 0)
>> -       if err != ENOSYS {
>> -               return err
>> -       }
>> +//     err = utimensat(_AT_FDCWD, path,
>> (*[2]Timespec)(unsafe.Pointer(&ts[0])), 0)
>> +//     if err != ENOSYS {
>> +//             return err
>> +//     }
>>         // If the utimensat syscall isn't available (utimensat was
>> added to Linux
>>         // in 2.6.22, Released, 8 July 2007) then fall back to utimes
>>         var tv [2]Timeval
>> --cut here--
>>
>> 11491 stat("/tmp/_Go_TestChtimes581938713", {st_mode=S_IFREG|0600,
>> st_size=13, ...}) = 0
>> 11491 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
>> 11491 utimes("/tmp/_Go_TestChtimes581938713", {{1360336212, 0},
>> {1360336212, 0}}) = 0
>> 11491 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
>> 11491 stat("/tmp/_Go_TestChtimes581938713", {st_mode=S_IFREG|0600,
>> st_size=13, ...}) = 0
>>
>> It looks to me that gcc miscompiles this part for some reason...?
>
> A miscompilation seems fairly unlikely.  I expect it's something very
> obvious, I'm just not seeing it.  Can you verify that the code reaches
> the stub definition of utimensat in libgo/runtime/go-nosys.c?

utimensat returns zero on CentOS. Following is gdb session:

Breakpoint 1, syscall.UtimesNano (path=..., ts.param=...) at
../../../gcc-svn/trunk/libgo/go/syscall/libcall_linux_utimesnano.go:13
13      func UtimesNano(path string, ts []Timespec) (err error) {
(gdb) n
14              if len(ts) != 2 {
(gdb) n
13      func UtimesNano(path string, ts []Timespec) (err error) {
(gdb) n
14              if len(ts) != 2 {
(gdb) n
17              err = utimensat(_AT_FDCWD, path,
(*[2]Timespec)(unsafe.Pointer(&ts[0])), 0)
(gdb) n
17              err = utimensat(_AT_FDCWD, path,
(*[2]Timespec)(unsafe.Pointer(&ts[0])), 0)
(gdb) n
18              if err != ENOSYS {
(gdb) p err
$1 = {__methods = 0x0, __object = 0x0}
(gdb) n
19                      return err
(gdb) n
29      }
(gdb) n
os.Chtimes (name=..., atime.param=..., mtime.param=...) at file_posix.go:162
162             return nil
(gdb) c
Continuing.
--- FAIL: TestChtimes (41.09 seconds)
os_test.go:681:         AccessTime didn't go backwards;
was={63495938759 0 46912511898976}, after={63495938759 0
46912511898976}
os_test.go:685:         ModTime didn't go backwards; was={63495938759
0 46912511898976}, after={63495938759 0 46912511898976}
FAIL

Uros.


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