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Re: [PATCH] i386: Assembly Implementation cleanup
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Wed, 12 Aug 2015 07:47:22 -0700
- Subject: Re: [PATCH] i386: Assembly Implementation cleanup
- Authentication-results: sourceware.org; auth=none
- References: <5596AD3B dot 1060903 at linaro dot org> <CAMe9rOof5LzNfW_Yd2qgtX2=UMdP-E-ewdneJ9GjiCF9SPyNqQ at mail dot gmail dot com> <55CB3E37 dot 8080006 at linaro dot org> <CAMe9rOr6a+iNtDjx6xT3KWYsyetpDswu8Zm8rQiJWS9CtP5f6w at mail dot gmail dot com> <55CB50F8 dot 8010504 at linaro dot org>
On Wed, Aug 12, 2015 at 6:58 AM, Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
>
> On 12-08-2015 09:44, H.J. Lu wrote:
>> On Wed, Aug 12, 2015 at 5:38 AM, Adhemerval Zanella
>> <adhemerval.zanella@linaro.org> wrote:
>>>
>>>
>>> On 11-08-2015 21:22, H.J. Lu wrote:
>>>> On Fri, Jul 3, 2015 at 8:41 AM, Adhemerval Zanella
>>>> <adhemerval.zanella@linaro.org> wrote:
>>>>> This patch removes i386 assembly implementation for epoll_wait, mmap,
>>>>> mmap64, semtimeop now that i386 have 6 argument syscall support from
>>>>> C code.
>>>>>
>>>>> The mmap implementation used is the wordsize-32 generic linux one.
>>>>>
>>>>> Tested in i386.
>>>>>
>>>>> ---
>>>>>
>>>>> * sysdeps/unix/sysv/linux/i386/mmap.c: New file.
>>>>> * sysdeps/unix/sysv/linux/i386/epoll_pwait.S: Remove file.
>>>>> * sysdeps/unix/sysv/linux/i386/mmap.S: Likewise.
>>>>> * sysdeps/unix/sysv/linux/i386/mmap64.S: Likewise.
>>>>> * sysdeps/unix/sysv/linux/i386/semtimedop.S: Likewise.
>>>>>
>>>>
>>>> What is the motivation? 6 argument syscalls aren't really inlined.
>>>> They put arguments on stack and call __libc_do_syscall. It is
>>>> slower than assembly code.
>>>>
>>>
>>> Same for ARM: code maintainability on functions that are not really
>>> performance-critical. This avoids issues like the x86 pthread_cond_*
>>> assembly implementation (which are now aimed to be removed), that
>>> required specific fixes just for x86.
>>
>> Is there a way to truly inline syscall with 6 arguments, not by calling
>> __libc_do_syscall?
>>
>
> I checked around some other projects that implements i386 syscall and
> neither seems to have a workaround for this. I also recall that Joseph
> has said GCC does not really support to not cobbler the required register,
> so that's why he has implemented through a helper function. Anyway, as
> Tovarld has asked, I think these are not really heavy hitter (and kernel
> implementation is much more complex than the time to save/restore the
> register in stack).
Let me take a look on this.
--
H.J.