[gentoo-user] Re: CPU upgrade and LVM questions.

[Nikos Chantziaras <realnc@gmail.com>]

On 07/12/2018 07:10, Dale wrote:
> Now this is odd.  I changed the settings and ran emerge.  I decided to
> use -UDNa options to see if it would catch the changes.  It did.  Thing
> is, outside a few video type packages, there were no packages to be
> rebuilt.  It seems very few packages actually notice those settings.

That's correct. Some software has compile-time flags to enable/disable 
specific CPU features. The ebuilds for that software use CPU_FLAGS_X86 
to enable the relevant compile-time flags.

Most software doesn't contain low-level assembly code. Software that 
does usually deals with video, audio or graphics, where hand crafted 
low-level optimizations by the developers make sense.

If you want to see all of the installed packages that are affected, you 
need to set CPU_FLAGS_X86 to an empty string:

   CPU_FLAGS_X86=""

and then do "emerge -puDN --with-bdeps=y @world". This is because 
CPU_FLAGS_X86 is not empty by default. It contains sse and sse2 by 
default, because these are supported by all 64-bit CPUs.


> My only question left, will those flags affect the kernel image itself?
> I may just have to make sure my USB stick works.

No. The kernel configuration is completely separate from anything in 
make.conf. CFLAGS or CPU_FLAGS_X86 do not affect kernel builds.