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 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.

-- 
H.J.