Re: [PATCH, resend] Add x86 32 bit vDSO time function support

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Jan 12, 2015 at 9:35 AM, Adhemerval Zanella
<azanella@linux.vnet.ibm.com> wrote:
> On 12-01-2015 13:59, H.J. Lu wrote:
>> On Mon, Jan 12, 2015 at 6:49 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>> On Mon, Jan 12, 2015 at 6:28 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>> On Mon, Jan 12, 2015 at 5:51 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>> On Tue, Jan 6, 2015 at 6:35 AM, Adhemerval Zanella
>>>>> <azanella@linux.vnet.ibm.com> wrote:
>>>>>> Ping.
>>>>>>
>>>>>> On 09-12-2014 13:32, Adhemerval Zanella wrote:
>>>>>>> Linux 3.15 adds support for clock_gettime, gettimeofday, and time vDSO
>>>>>>> (commit id 37c975545ec63320789962bf307f000f08fabd48).  This patch adds
>>>>>>> GLIBC supports to use such symbol when they are avaiable.
>>>>>>>
>>>>>>> Along with x86 vDSO support, this patch cleanup x86_64 code by moving
>>>>>>> all common code to x86 common folder.  Only init-first.c is different
>>>>>>> between implementations.
>>>>>>>
>>>>>>> Tested on x86 and x86_64 with a 3.5.0 and a 3.16 kernel.
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>>> 2014-12-09  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
>>>>>>>           Stefani Seibold  <stefani@seibold.net>
>>>>>>>
>>>>>>>       * sysdeps/unix/sysv/linux/x86_64/Makefile [$(subdir) = elf]
>>>>>>>       (sysdep_routines): Add dl-vdso here, ...
>>>>>>>       * sysdeps/unix/sysv/linux/x86/Makefile [$(subdir) = elf]
>>>>>>>       (sysdep_routines): ... not here.
>>>>>>>       * sysdeps/unix/sysv/linux/i386/gettimeofday.c: New file: set syscall
>>>>>>>       fallback when vDSO is not presented.
>>>>>>>       * sysdeps/unix/sysv/linux/x86_64/init-first.c (__vdso_clock_gettime):
>>>>>>>       Define with libc_hidden_proto/libc_hidden_data_def definitions.
>>>>>>>       (_libc_vdso_platform_setup): Rename to __vdso_platform_setup.
>>>>>>>       * sysdeps/unix/sysv/linux/i386/init-first.c: New file: likewise.
>>>>>>>       * sysdeps/unix/sysv/linux/i386/time.c: New file: likewise.
>>>>>>>       * sysdeps/unix/sysv/linux/x86_64/bits/libc-vdso.h: Moved to ...
>>>>>>>       * sysdeps/unix/sysv/linux/x86/libc-vdso.h: ... here.
>>>>>>>       * sysdeps/unix/sysv/linux/x86_64/clock_gettime.c: Move to ...
>>>>>>>       * sysdeps/unix/sysv/linux/x86/clock_gettime.c: ... here.
>>>>>>>       * sysdeps/unix/sysv/linux/x86_64/gettimeofday.c: Move to ...
>>>>>>>       * sysdeps/unix/sysv/linux/x86/gettimeofday.c: ... here.  Also added
>>>>>>>       fallback configurable symbol when vDSO is not available.
>>>>>>>       * sysdeps/unix/sysv/linux/x86_64/time.c: Move to ...
>>>>>>>       * sysdeps/unix/sysv/linux/x86/time.c: ... here.  Also refactored to
>>>>>>>       be able to redefine fallback symbol when vDSO is not available.
>>>>>>>       * sysdeps/unix/sysv/linux/x86_64/timespec_get.c: Move to ...
>>>>>>>       * sysdeps/unix/sysv/linux/x86/timespec_get.c: ... here.
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>>> +# include <dl-vdso.h>
>>>>>>> +# include <errno.h>
>>>>>>> +
>>>>>>> +/* If the vDSO is not available we fall back on the syscall.  */
>>>>>>> +static int
>>>>>>> +__gettimeofday_syscall (struct timeval *tv, struct timezone *tz)
>>>>>>> +{
>>>>>>> +  return INLINE_SYSCALL (gettimeofday, 2, tv, tz);
>>>>>>> +}
>>>>>>> +# define GETTIMEOFAY_FALLBACK (void*) (&__gettimeofday_syscall)
>>>>>>> +# undef libc_ifunc_hidden_def
>>>>>>> +# define libc_ifunc_hidden_def(name)  \
>>>>>>> +  libc_ifunc_hidden_def1 (__GI_##name, __gettimeofday_syscall)
>>>>> Why do you define __GI___gettimeofday to __gettimeofday_syscall
>>>>> instead of the ifunc version? The x86-64 ifunc  works fine.
>>>>>
>>>>> --
>>>>> H.J.
>>>> Why isn't __GI_time IFUNC
>>>>
>>>> 5822: 000a3360    21 FUNC    LOCAL  DEFAULT   13 __GI_time
>>>>
>>> The key to call local IFUNC function is that we HAVE to tell GCC
>>> it is a global function, not local so that it will go through PLT.
>>> Otherwise GCC will perform optimization which will break local
>>> IFUNC.  I will see what I can do.
>>>
>> This requires too many changes with unknown benefits at this stage.  OK with
>> copyright year update and sysdeps/unix/sysv/linux/x86_64/x32/init-first.c
>> fix.
>>
>> Thanks.
>>
> The idea of this patch is to just provide IFUNC calls externally to GLIBC, internal
> calls are still by the syscall.  I didn't really dig into the issues, but what I
> could tell i386 suffers from the same issue as powerpc32: __gettimeofday is resolved
> as a local call and thus no PLT is created, although the IFUNC is still called.

The problem on i386 is EBX wasn't set up for calling IFUNC via PLT since
it is local.

> I will change the copyright and the x32 and push, thanks for the review.
>



-- 
H.J.