Re: [gentoo-user] USE="mmx mmxext sse sse2 ssse3 3dnow 3dnowext"

[Alan McKinnon <alan.mckinnon@gmail.com>]

On Wednesday 27 May 2009 00:20:50 KH wrote:
> Hi,
>
> so I temporarily disable all USE flags in my make.conf by adding the "#"
> to the line. Some with package.use.
> The I run :
>
> USE="cpudetection" emerge -pv mplayer
>
> See output below.
>
> So what changes for me: oss is added. That's nothing for hardware and I
> use alsa, so I don't need it, do I?
> -aalib -cddb -cdparanoia -debug -dirac -dvb (not hardware)
> -pvr (it's software too, isn't it?)
> -samba -schroedinger -xinerama (not hardware)
>
>
> Is this a valid way of approache?
>
> So My USE flags are set correct (for hardware) aren't they?

No, you have it wrong.

The ebuild does not magically change the USE flags based on what you have. It 
will build according to what you tell it, no more, no less.

USE=cpudetection causes special code to be compiled into mplayer. Think of it 
this way (a highly simplistic explanation that gets the point across):

mplayer is built with routines for every possible optimization. At RUNTIME, 
when mplayer starts, it figures out what you have and what you can use, and 
remembers for itself the routines you can't use and does not run them.

cpudetection changes runtime behaviour, not compile time behaviour, and does 
not change your use flags at all. When you hashed out the line in 
/etc/make.conf, all you proved is that with the exception of oss, your 
configured USE flags for mplayer are the same as the default for your profile 
and mplayer.

-- 
alan dot mckinnon at gmail dot com