Re: Cross-building bootstrap binaries fail in current master

[Carlos Sánchez de La Lama]

Hi!

> Regardless, cross-building ‘bootstrap-tarballs’ to one of the supported
> target triplets works on master:
>
> --8<---------------cut here---------------start------------->8---
> $ ./pre-inst-env guix build bootstrap-tarballs --target=mips64el-linux-gnu -n
> substitute: updating list of substitutes from 
> 'https://mirror.hydra.gnu.org'... 100.0%
> The following files would be downloaded:
>    /gnu/store/lwn9v9jhsllffpc3d4kii8bldw4hfppa-bootstrap-tarballs-0
>    
> /gnu/store/6cm18hfwbp8c1mf6wha28f0b0axlcm8k-guile-static-stripped-tarball-2.0.11
>    /gnu/store/f790i196x1ms2ym13pvbazldzicqv4k9-glibc-stripped-tarball-2.23
>    /gnu/store/jj007dw6gc31hnn1qq3yz7rz1ai1z0fa-gcc-stripped-tarball-4.9.3
>    /gnu/store/niqxni4hhjr2wvlabn92z1asqb7xcnsx-static-binaries-tarball-0
>    
> /gnu/store/pskf0y5q3j5a3k30c0czd2xymwp4224i-binutils-static-stripped-tarball-2.25.1
> $ git describe
> v0.11.0-1764-g3ad7dce
> --8<---------------cut here---------------end--------------->8---
>
> See:
>
>   
> https://hydra.gnu.org/job/gnu/master/mips64el-linux-gnu.bootstrap-tarballs-0.x86_64-linux
>   
> https://hydra.gnu.org/job/gnu/master/mips64el-linux-gnuabi64.bootstrap-tarballs-0.x86_64-linux

For efraim and for myself,

guix build --target=mips64el-linux-gnu bootrap-tarballs

got broken with commit

b9bc6e842066b066ebdf9eaf75d41753598d75b5

After some digging, I think I have found the root cause. That commit
introduces a (otherwise fine) replacement for expat, but this triggers a
problem:

After package-cross-derivation has (sucesfully) cross-built the
un-grafted bootstrap-tarballs derivation, it tries to resolve grafts,
using (bag-grafts), which does:

--8<---------------cut here---------------start------------->8---
  (define target-grafts
    (if target
        (let ((->graft (input-cross-graft store target system)))
          (fold-bag-dependencies (lambda (package grafts)
                                   (match (->graft package)
                                     (#f    grafts)
                                     (graft (cons graft grafts))))
                                 '()
                                 bag
                                 #:native? #f))
--8<---------------cut here---------------end--------------->8---

Now, (fold-bag-dependencies) goes trhough *all* the dependencies, down to
make-boot0. The replacement in expat causes this loop to apply
(package-cross-derivation) to them, including those which are not
cross-compilable, at which point building fails (make-boot0).

Probably building with --no-grafts is a suitable work-around, or
cross-building expat beforehand (thus I won't need grafting) but I am
leaving my store untoched for a while to be able to produce a proper
fix.

BR

Carlos