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Re: [PATCH] x86-64: Implement strcat family IFUNC selectors in C
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: libc-alpha at sourceware dot org
- Date: Thu, 15 Jun 2017 12:32:23 -0300
- Subject: Re: [PATCH] x86-64: Implement strcat family IFUNC selectors in C
- Authentication-results: sourceware.org; auth=none
- References: <20170612161054.GD25262@gmail.com>
On 12/06/2017 13:10, H.J. Lu wrote:
> Implement strcat family IFUNC selectors in C.
> All internal calls within libc.so can use IFUNC on x86-64 since unlike
> x86, x86-64 supports PC-relative addressing to access the GOT entry so
> that it can call via PLT without using an extra register. For libc.a,
> we can't use IFUNC for functions which are called before IFUNC has been
> initialized. Use IFUNC internally reduces the icache footprint since
> libc.so and other codes in the process use the same implementations.
> This patch uses IFUNC for strcat family functions within libc.
> Any comments?
> * sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
> * sysdeps/x86_64/multiarch/strcat-sse2.S: New file.
> * sysdeps/x86_64/multiarch/strcat.c: Likewise.
> * sysdeps/x86_64/multiarch/strncat.c: Likewise.
> * sysdeps/x86_64/multiarch/strcat.S: Removed.
> * sysdeps/x86_64/multiarch/strncat.S: Likewise.
LGTM, but since the idea is to use IFUNC for internal symbol call, do we
still need the assembly implementation for x86_64? Default algorithm should
be good enough with both vectorized strlen and strcpy (same for strncat)