bug#55431: [PATCH] guix: cpu: recognize other architectures.

[Efraim Flashner]

On Sun, May 15, 2022 at 07:11:32PM +0200, Julien Lepiller wrote:
> Hi Guix!
> 
> The attached patch lets (guix cpu) recognize other architectures. The
> code of (current-cpu) is based on the content of /proc/cpuinfo which
> can be pretty different on non-intel architectures. For instance,
> here's a sample from an armhf machine:
> 
> processor     : 0
> model name    : ARMv7 Processor rev 4 (v7l)
> BogoMIPS      : 45.47
> Features      : half thumb fastmult vfp edsp thumbee neon vfpv3 tls
> vfpv4 idiva idivt vfpd32 lpae evtstrm CPU implementer : 0x41
> CPU architecture: 7
> CPU variant   : 0x0
> CPU part      : 0xc07
> CPU revision  : 4
> 
> In particular, there's no flags entry, so (current-cpu) doesn't stop
> until eof, and returns #f.
> 
> It's an issue because a test uses this code, for testing manifests with
> --tune. If no cpu is returned, the test crashes:
> 
> In guix/transformations.scm:
>    864:25  1 (_ _ _ _ ((package ad-hoc-package "gcc-toolchain")
> (<E2><80><A6>) <E2><80><A6>)) In guix/cpu.scm:
>      94:2  0 (cpu->gcc-architecture #f)
> 
> Since the test fails, the "guix" package doesn't build, and I can't
> reconfigure on armhf or aarch64. (well armhf has other issues right
> now...)
> 
> The attached patch changes the logic of the code to read all lines,
> find information about the CPU even if it's an ARM CPU, and returns
> always something (to prevent the crash) when it reads eof. This means
> that it will return architecture information about the last CPU,
> instead of the first. I don't think that's an issue because this code
> is used for --tune which really only works on intel where you don't
> have multiple CPUs with too different features.
> 
> WDYT?

I just pushed mine without seeing yours, sorry.

I did check the gcc source code and I found the options for determining
the cpu flags for arm* processors in gcc/config/arm/arm-cpus.in. Do you
think it'd be worth it to add detection for armv7 CPUs?

Also, I'm pretty sure we can overlap armhf and aarch64 together, and
i686 and x86_64 together, and then running 32-bit code on 64-bit
processors will get a nice boost since it'll be tuned for the actual
hardware.

-- 
Efraim Flashner   <efraim@flashner.co.il>   אפרים פלשנר
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