RFC: Check GLIBC_IFUNC to enable/disable ifunc features

[H.J. Lu]

On Sun, Jun 26, 2016 at 3:08 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Sun, Jun 26, 2016 at 11:55 AM, Carlos O'Donell <carlos@redhat.com> wrote:
>> On 06/26/2016 10:50 AM, H.J. Lu wrote:
>>> Hi,
>>>
>>> I'd like to check IFUNC_XXX environmental variable to enable/disable
>>> the ifunc feature, XXX.  That is
>>>
>>> 1.  IFUNC_XXX=1 to enable XXX.
>>> 2.  IFUNC_XXX=0 to disable XXX.
>>>
>>> Any comments?
>>
>> How would it work? Does it just mean that the IFUNC selector bypasses
>> the disabled choices?
>
> It will override bits in dl_x86_cpu_features.
>
>> Also it does not meet Tunables consensus:
>> "Tunable namespace should be clearly defined"
>> https://sourceware.org/glibc/wiki/TuningLibraryRuntimeBehavior?highlight=%28Tunables%29
>>
>> Should perhaps be "GLIBC_<VER>_IFUNC_<ARCH>_<PUBLIC_IFUNC_NAME>"?
>
> They won't be version-dependent.  How about
>
> GLIBC_IFUNC_X86=sse2=0:....
>
> or
>
> GLIBC_IFUNC=sse2=0:....
>
> since IFUNC is target dependent.

Something like this.


-- 
H.J.
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