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Re: [PATCH, resend] Add x86 32 bit vDSO time function support
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Mon, 12 Jan 2015 06:49:01 -0800
- Subject: Re: [PATCH, resend] Add x86 32 bit vDSO time function support
- Authentication-results: sourceware.org; auth=none
- References: <54871622 dot 807 at linux dot vnet dot ibm dot com> <54ABF2A9 dot 5010306 at linux dot vnet dot ibm dot com> <CAMe9rOr40wq9+d-88A9MDG2m=FeEKG==KpRBCbfPtDBdUwGPNA at mail dot gmail dot com> <CAMe9rOow7kETLOOJ1reWyzZh2GU3tPv3N=6t=vUHRvtAcLOPXw at mail dot gmail dot com>
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.
--
H.J.