%current-system and --system

%current-system and --system

[Greg Hogan]

Hi Guix,

From my x86_64 machine I am executing offload builds targeting an
aarch64 machine:

$ guix build --system=aarch64-linux --manifest=manifest.scm

Several packages do not build for aarch64 and need to be filtered out.
%current-target-system is #f as these are offload builds not cross
compilation, and %current-system is reported as "x86_64-linux". How
can I access the current "build system"?

If it helps, the manifest is defined at
https://github.com/greghogan/guix-manifest

Thanks,
Greg

Re: %current-system and --system

[Efraim Flashner]

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On Fri, Mar 03, 2023 at 10:37:44AM -0500, Greg Hogan wrote:
> Hi Guix,
> 
> From my x86_64 machine I am executing offload builds targeting an
> aarch64 machine:
> 
> $ guix build --system=aarch64-linux --manifest=manifest.scm
> 
> Several packages do not build for aarch64 and need to be filtered out.
> %current-target-system is #f as these are offload builds not cross
> compilation, and %current-system is reported as "x86_64-linux". How
> can I access the current "build system"?
> 
> If it helps, the manifest is defined at
> https://github.com/greghogan/guix-manifest
> 
> Thanks,
> Greg

Here's a (reduced) snippet I have from my home-config (and previously in
my manifest file):

(define %my-package-list
  (list "git"
        "git:send-email"
        "git-annex")

(define package-list
  (map (compose list specification->package+output)
       (filter (lambda (pkg)
                 (member (or (%current-system)
                             (%current-target-system))
                         (package-transitive-supported-systems
                           (specification->package+output pkg))))
              %my-package-list)))

(%current-target-system) doesn't currently work with guix-home but I
figured I'd have it ready. package-transitive-supported-systems makes it
so that git-annex, which shows as supported on aarch64-linux, isn't
added because ghc, one of its dependencies, isn't supported on
aarch64-linux.


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Re: %current-system and --system

[Ludovic Courtès]

Hi,

Greg Hogan <code@greghogan.com> skribis:

> From my x86_64 machine I am executing offload builds targeting an
> aarch64 machine:
>
> $ guix build --system=aarch64-linux --manifest=manifest.scm
>
> Several packages do not build for aarch64 and need to be filtered out.
> %current-target-system is #f as these are offload builds not cross
> compilation, and %current-system is reported as "x86_64-linux". How
> can I access the current "build system"?

Not via ‘%current-system’ because at the time the manifest is evaluated,
it can be bound to anything, as you saw.

What you could do is wrap packages in ‘let-system’, which lets you check
the “current system” as the time the object is “lowered” (untested):

  (define (package-or-emptiness p)
    (let-system system
      (if (supported-package? p system)
          p
          (plain-file "emptyness" "Nothing to see here."))))

   (manifest
    (map (lambda (p)
           (manifest-entry
             (inherit (package->manifest-entry p))
             (item (package-or-emptiness p))))
         the-packages))

Obviously that’s not great because you still end up with entries for
non-existing packages.  It’s good enough for ‘guix build -m’ though.

HTH!

Ludo’.