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List:       glibc-help
Subject:    Build and test memory functions in glibc-2.25
From:       adhemerval.zanella () linaro ! org (Adhemerval Zanella)
Date:       2017-03-27 17:29:00
Message-ID: 84f928bc-c42c-774f-d055-a4542e79d33f () linaro ! org
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On 27/03/2017 13:01, Lu, Hongjiu wrote:
> Hi hongjiu and glibc developers,
> 
> I was investigating whether a few memory functions(memcpy, memset, memmove) with \
> various versions(sse4, ssse3, avx2, avx512) in glibc-2.25 could have performance \
> gain for our server programs in Linux(glibc 2.12). I put the detailed question on \
> stackoverflow(http://stackoverflow.com/questions/42999511/port-glibc-2-25-and-test-memory-functions). \
> In short, my questions are as follows: 
> 1. I built glibc-2.25 on my dev machine and run my application under newly built \
> glibc. Then did the glibc select the most suitable version of memory functions \
> automatically for me according to the cpu/os/memory? 
> That is correct.
> 
> H.J.
> ----
> 2. If #1?s answer is no, do I need to tweak a few options for ./configuration and \
> make to achieve that?

Default configure option for x86_64 is to enable ifunc (or multi-arch in glibc \
terminology) as default. So, unless you actually configured glibc with \
--disable-multi-arch you will have ifunc enabled.

> 
> 3. If #2 is impossible, I was wondering if I need to dispatch the \
> memcpy/memset/memmove calls to the appropriate version of functions with \
> __attribute__((ifunc))( https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40528 ) \
> manually according to the corresponding boolean test of the cpu(Built-in Function: \
> int __builtin_cpu_supports (const char *feature))?  
> I reviewed changelog and the related links above and put hongjiu on the list \
> explicitly. Please help take a look and I?m looking forward to your replies. 
> Thanks in advance.
> 
> ________________________________________
> wentingli(???)
> 


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