Re: [PATCH] powerpc: New feature - HWCAP/HWCAP2 bits in the TCB

[Richard Henderson <rth at twiddle dot net>]

On 06/30/2015 04:07 PM, Steven Munroe wrote:
> On Tue, 2015-06-30 at 07:49 +0100, Richard Henderson wrote:
> This is not intended for use within GLIBC or by knowledgeable folks like
> yourself and the GLIBC community.
>
> This about application developers in other communities and users where I
> would settle for them to just support my platform with any optimization
> that is somewhat sane.
>
> The __Builtin_cpu_supports exist and I see its use. I don't see much use
> of the more "complicated" approaches that we use in GLIBC. So it seem
> reasonable to enable __builtin_cpu_supports for POWER but define the
> implementation to be optimal for the PowerPC platform.
>
> Most the argument against seems to be based on assumed "moral hazard".
> Where you think what they are doing is stupid and so you refuse to help
> them with any mechanisms that might make what they are doing, and will
> continue to do, a little less stupid.

No, this is mostly an argument against adding a new dependency between glibc 
and gcc, at a specific glibc version, which cannot be checked via symbol 
versioning.

On the other hand, there is an alternative way to implement what you want that, 
while a factor of 20 slower is not "slow" when the interface is used at the 
"approprate" level.  And further, that the interface *is* handled by symbol 
versioning, and is also present in an older version of glibc and so the gcc 
feature is usable on more systems.

Surely that's a consideration worth a counter-argument?


r~