Re: Cross-building GuixSD (and maybe using pre-built toolchains)

[ludo@gnu.org (Ludovic Courtès)]

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ludo@gnu.org (Ludovic Courtès) skribis:

> David Craven <david@craven.ch> skribis:
>
>>>> So one issue that happens when cross building is for things that have
>>>> the #:no-substitutes #t enabled. This is mainly found in service
>>>> derivations for generating configuration files.
>>>
>>> I think there’s currently no easy way to cross build a full GuixSD
>>> anyway, like ‘guix system build --target=mips64el-linux-gnu’ (the
>>> --target flag doesn’t exist yet).  Or did you experiment in this area?
>>>
>>> I’d be curious.  It’s designed to allow this (in particular because
>>> gexps are cross-compilation-aware), but I’ve never tried.
>>
>> I'm currently not trying to cross-compile everything. The
>> --system=mips64el-linux gets us pretty far already. The missing parts
>> are only the ones where no substitutes are available.
>
> Aaah OK.  That’s not cross-compilation though, so it works if and only
> if substitutes are available or builds can be offloaded to a machine of
> that architecture.  Otherwise it cannot really work.
>
> Now, in most cases, the tiny Guile derivations created via
> ‘gexp->derivation’ et al. in GuixSD (e.g., the derivation that builds
> the initrd) could use, say, an x86_64 Guile, even if building for
> mips64el.  However, it would be difficult to take advantage of this
> AFAICS.

There’s an untested hack to illustrate:


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diff --git a/guix/gexp.scm b/guix/gexp.scm
index 302879f..53239ac 100644
--- a/guix/gexp.scm
+++ b/guix/gexp.scm
@@ -523,6 +523,8 @@ The other arguments are as for 'derivation'."
             (cons file-name thing)))
          graphs))
 
+  (define gsystem "x86_64-linux")
+
   (mlet* %store-monad (;; The following binding forces '%current-system' and
                        ;; '%current-target-system' to be looked up at >>=
                        ;; time.
@@ -546,13 +548,13 @@ The other arguments are as for 'derivation'."
                                             (object->string sexp)))
                        (modules  (if (pair? %modules)
                                      (imported-modules %modules
-                                                       #:system system
+                                                       #:system gsystem
                                                        #:module-path module-path
                                                        #:guile guile-for-build)
                                      (return #f)))
                        (compiled (if (pair? %modules)
                                      (compiled-modules %modules
-                                                       #:system system
+                                                       #:system gsystem
                                                        #:module-path module-path
                                                        #:guile guile-for-build)
                                      (return #f)))
@@ -587,7 +589,7 @@ The other arguments are as for 'derivation'."
                         ,builder)
                       #:outputs outputs
                       #:env-vars env-vars
-                      #:system system
+                      #:system gsystem
                       #:inputs `((,guile)
                                  (,builder)
                                  ,@(if modules
diff --git a/guix/packages.scm b/guix/packages.scm
index 3646b9b..fe23d35 100644
--- a/guix/packages.scm
+++ b/guix/packages.scm
@@ -1104,7 +1104,7 @@ symbolic output name, such as \"out\".  Note that this procedure calls
   "This monadic procedure changes the Guile currently used to run the build
 code of derivations to GUILE, a package object."
   (lambda (store)
-    (let ((guile (package-derivation store guile)))
+    (let ((guile (package-derivation store guile "x86_64-linux")))
       (values (%guile-for-build guile) store))))
 
 (define* (package-file package

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Ludo’.