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Re: [PATCH] x86-64: Implement strcat family IFUNC selectors in C



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?
> 
> H.J.
> 	* sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
> 	strcat-sse2.
> 	* 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)


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