[gentoo-dev] Re: Move x86/amd64 CPU extensions USE flags to a new USE_EXPAND variable

[Duncan]

Dirkjan Ochtman posted on Sat, 11 Dec 2010 20:03:39 +0100 as excerpted:

> On Sat, Dec 11, 2010 at 20:01, Matt Turner <mattst88@g.o> wrote:
>> I agree that this could be better. To me, most of the problems with
>> this are due to users not knowing which of these should be set for
>> their particular CPU.
>>
>> Instead of having defaults set by a profile, I'd like to figure out a
>> way we can have these flags set by default dependent on the user's CPU.
>> This might require some additional logic in portage; I don't know.
>
> Yeah, I think setting the best possible default is important here.

FWIW, I don't think that's a good idea -- at least if you're suggesting 
real-time build-machine detection (see below for the alternative).  Not 
only will implementing it be a lot of work, but then you'll have people 
filing bugs because they intended to compile for several different 
machines and set generic CFLAGS accordingly, but still ended up with 
broken packages because the default CPU extensions logic looked at the 
build machine only, and they thought they were done when they set the 
profile, CFLAGS and CHOST to the level of generic they intended.

Unless the logic is based on the -march set in C(XX)FLAGS.  That could 
work, as people should already be setting that as specific or generic as 
they want.

I do like the USE_EXPAND idea, tho.

Meanwhile, would it be possible to have altivec in the same USE_EXPAND?  
It's the same CPU extensions type of thing on PPC, if I'm not mistaken.  
Does profile-mask work for USE_EXPAND?  Because it just seems strange to 
me to see all those CPU extensions in their own USE_EXPAND and see altivec 
still in USE.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman