Re: [PATCH] S390: Refactor ifunc handling

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 30/11/2018 13:57, Stefan Liebler wrote:
> This patch series is mainly refactoring the s390 specific ifunc handling.
> The idea is to omit ifunc variants or ifunc at all if the used compile
> options are already building for newer cpus. The glibc internal calls
> and ld.so will then use "newer" ifunc variants as before.
> 
> In case of the memcpy, memset and memcmp functions, the newest ifunc variant
> is for z196 and there are two further ones for older cpus, but the current usual
> compile options are e.g. building for zEC12.
> In case of the string / wcsmbs functions, there are variants for z13 and
> "before z13".  After switching to z13 as default cpu level, there won't
> be IFUNC symbols in s390 libc.so.
> 
> Furthermore new z13 specific ifunc variants are introduced for
> memmove, strstr and memmem.
> 
> Some functions like the mem* functions are duplicated twice for 31 and 64 bit.
> In fact they are nearly the same. Thus those implementations are now unified
> and adjusted in order to be usable for 31 and 64bit.
> 
> I've build and tested these patches with different -march levels
> and with / without multiarch and checked the symbols with readelf - e.g. if
> IFUNC is used or not and if the __GI_ symbols are targeting the correct
> ifunc variant.
> 
> If no one objects, I plan to commit this series in the next one or two weeks.
> 

The only issue I have for this change is it would require another
ABI variant for testing and validation, which would require more
coverage from build-many-glibcs.py (similar to armv7 for instance).

The gains I see is a slight reduction is loading time (due no ifunc)
and less code side. Is is what is driving you for this change? Does
it worth the extra testing and validation it might require?