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Re: [PATCH] i386: Assembly Implementation cleanup
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Wed, 12 Aug 2015 10:58:16 -0300
- 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>
On 12-08-2015 09:44, H.J. Lu wrote:
> On Wed, Aug 12, 2015 at 5:38 AM, Adhemerval Zanella
> <email@example.com> wrote:
>> On 11-08-2015 21:22, H.J. Lu wrote:
>>> On Fri, Jul 3, 2015 at 8:41 AM, Adhemerval Zanella
>>> <firstname.lastname@example.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
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).