ld-wrapper is broken in core-updates due to guile-2.2 (host running guile-2.0)

[Sergei Trofimovich <slyfox@inbox.ru>]

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Efraim noticed core-updates breakage on package libgpg-error.

TL;DR:

  ld-wrapper package embeds guile-2.2 interpreter
  to interpret ld.go bytecode built by guile-2.0.
  I have no idea how to fix it but still decided to
  share my findings so far.

Longer story:

The sympthon is broken ld:

    $ ./pre-inst-env guix build libgpg-error
    ...
    checking whether the C compiler works... no
    configure: error: in `/tmp/guix-build-libgpg-error-1.26.drv-0/libgpg-error-1.26':
    configure: error: C compiler cannot create executables
    See `config.log' for more details

Namely minimal linking (from config.log) fails as:

  configure:3724: checking whether the C compiler works
  configure:3746: gcc    conftest.c  >&5
  Backtrace:
           5 (apply-smob/1 #<catch-closure 1d14100>)
  In ice-9/boot-9.scm:
    710:2  4 (call-with-prompt ("prompt") #<procedure 1d286a0 at ic?> ?)
  In ice-9/eval.scm:
    619:8  3 (_ #(#(#<directory (guile-user) 1dd01e0>)))
  In ice-9/command-line.scm:
   181:18  2 (_ #<input: string 1dfff50>)
  In unknown file:
           1 (eval (load-compiled "/gnu/store/qv0w20gdi57ybganx82?") #)
           0 (load-compiled/vm "/gnu/store/qv0w20gdi57ybganx82w8ymk1?")

  ERROR: In procedure load-compiled/vm:
  ERROR: In procedure load-thunk-from-memory: No such file or directory
  collect2: error: ld returned 1 exit status
  configure:3750: $? = 1
  configure:3788: result: no
  configure: failed program was:
  | /* confdefs.h */
  | int
  | main ()
  | {
  |   return 0;
  | }
  configure:3793: error: in `/tmp/guix-build-libgpg-error-1.26.drv-0/libgpg-error-1.26':
  configure:3795: error: C compiler cannot create executables
  See `config.log' for more details

That's right: it's the guile's backtrace from gcc invocation.
  /tmp/guix-build-libgpg-error-1.26.drv-0/libgpg-error-1.26 $ ld
  Backtrace:
           5 (apply-smob/1 #<catch-closure ae2c20>)
  In ice-9/boot-9.scm:
    710:2  4 (call-with-prompt ("prompt") #<procedure aefa40 at ice…> …)
  In ice-9/eval.scm:
    619:8  3 (_ #(#(#<directory (guile-user) b781e0>)))
  In ice-9/command-line.scm:
   181:18  2 (_ #<input: string ba5f50>)
  In unknown file:
           1 (eval (load-compiled "/gnu/store/qv0w20gdi57ybganx82…") #)
           0 (load-compiled/vm "/gnu/store/qv0w20gdi57ybganx82w8ymk1…")

  ERROR: In procedure load-compiled/vm:
  ERROR: In procedure load-thunk-from-memory:

Backtrace tries to tell us that guile-2.2 cannot load ld.go file. Snippet from `which ld`:

  """
  exec /gnu/store/kri8a2dy6dy0cdg0z41djn0pnn08515z-guile-2.2.0/bin/guile -c "(load-compiled \"/gnu/store/qv0w20gdi57ybganx82w8ymk1cwv7n2c-ld-wrapper-0/bin/ld.go\") (apply $main (cdr (command-line)))" "$@"
  """

File confirms bytecode is from incompatible 2.0 version:

  $ file /gnu/store/qv0w20gdi57ybganx82w8ymk1cwv7n2c-ld-wrapper-0/bin/ld.go
  /gnu/store/qv0w20gdi57ybganx82w8ymk1cwv7n2c-ld-wrapper-0/bin/ld.go: Guile Object, little endian, 64bit, bytecode v2.0

I think the problem comes from 'gnu/packages/base.scm:make-ld-wrapper' function
which uses host's guile to compile ld.go, not bootstrapped guile:

http://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/base.scm#n458

(define* (make-ld-wrapper name #:key
                          (target (const #f))
                          binutils
                          (guile (canonical-package guile-2.0))
                          (bash (canonical-package bash))
                          (guile-for-build guile))
...
    (arguments
     (let ((target (target (%current-system))))
       `(#:guile ,guile-for-build
         #:modules ((guix build utils))
         #:builder (begin
...
                       (chmod ld #o555)
                       (compile-file ld #:output-file go))))))

Which guile is being used here for compile-file? 'build-for-build'
or current host's guile? Looks like the requirement here is that
both mush be of the same version.

If it really is a requirement to run guile-2.2 perhaps adding early
assertion would be nicer? I don't know how to add it either :)

Thanks!

-- 

  Sergei

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