Re: [gentoo-user] Re: Multilib ABI specific CPU use flags?

[Jonathan Yong]

On 10/9/20 9:27 AM, Ashley Dixon wrote:
> On Fri, Oct 09, 2020 at 12:26:17AM +0000, Jonathan Yong wrote:
>> I'm open to fixing ebuild packages by myself in my own overlay, though I
>> prefer not to due to eventual bit rot. Any hints on how to mask CPU USE
>> flags based on multilib arch in the .ebuild file itself?
>
> I suppose you could detect whether a CPU_FLAG is enabled for a x86_32  multilib,
> although be wary that `MULTILIB_ABI_FLAG` is only  exported  for  some  multilib
> functions, such as `multilib_src_configure` [1]:
>
>          if [[ ${MULTILIB_ABI_FLAG} == abi_x86_32 ]] && use cpu_flags_x86_avx2;
>          then
> 		ewarn "Disabling AVX2 extensions for 32-bit build."
> 		# circumvention measures
> 	fi
>
> I'm not sure of the best way to achieve the "circumvention measures", hence  the
> comment.  You could run this conditional after  GLOBALCMAKEARGS  has  been  set,
> omitting the CPU_BASELINE definition in the main block [2],  or  you  could  sed
> through the USE flags and disable `cpu_flags_x86_avx2` there.   You're  probably
> better asking on IRC for the best-practice way to achieve this.
>

OK, thanks for the hints, I had something similar when I tried 
/etc/portage/bashrc, so MULTILIB_ABI_FLAG is the variable to look out for.

I will try this next time if another package misbehaves with AVX2. I'm 
OK with trial and error learning.

> As mentioned in the relevant bug report, this is not  an  issue  caused  by  the
> ebuild, so although this might prove to be a temporary fix, it will hopefully be
> resolved by upstream very soon. Just be patient. ;-)
> > [1]
https://wiki.gentoo.org/wiki/Project:Multilib/multilib-build#MULTILIB_ABI_FLAG
> [2] https://github.com/opencv/opencv/wiki/CPU-optimizations-build-options#customizing-cmake-options
> [3] https://bugs.gentoo.org/747163#c15
>

I'm not so worried about OpenCV itself, since it is very much an active 
project.

The notion that I am unable to fix a problem myself, on a system that I 
own, because of some technicality, even as a temporary measure is 
disconcerting. Controlling every piece of how a software is configured, 
built and installed is why I love Gentoo's portage system so much.