cross-compilation regression on mirage

[emillon]

Our mirage CI run is broken. The linking step fails with:

/usr/bin/ld: /home/runner/work/dune/dune/mirage/_build/solo5/duniverse/Zarith/../../../install/default/lib/gmp//libgmp.a(assert.o): in function `__gmp_assert_header':
assert.c:(.text+0x36): undefined reference to `__fprintf_chk'
/usr/bin/ld: /home/runner/work/dune/dune/mirage/_build/solo5/duniverse/Zarith/../../../install/default/lib/gmp//libgmp.a(assert.o): in function `__gmp_assert_fail':
assert.c:(.text+0x9a): undefined reference to `__fprintf_chk'
/usr/bin/ld: /home/runner/work/dune/dune/mirage/_build/solo5/duniverse/Zarith/../../../install/default/lib/gmp//libgmp.a(assert.o): in function `__gmp_assert_header':
assert.c:(.text+0x6c): undefined reference to `__fprintf_chk'
/usr/bin/ld: /home/runner/work/dune/dune/mirage/_build/solo5/duniverse/Zarith/../../../install/default/lib/gmp//libgmp.a(memory.o): in function `__gmp_default_allocate':
memory.c:(.text+0x42): undefined reference to `__fprintf_chk'
/usr/bin/ld: /home/runner/work/dune/dune/mirage/_build/solo5/duniverse/Zarith/../../../install/default/lib/gmp//libgmp.a(memory.o): in function `__gmp_default_reallocate':
memory.c:(.text+0x95): undefined reference to `__fprintf_chk'
collect2: error: ld returned 1 exit status
File "caml_startup", line 1:

I bisected that to #8740. I'll try to isolate a repro case.

[emillon]

While diffing the logs, it looks like it picks the wrong context (- is the good build, + is the bad build)

 binary ocamldoc: found in /home/runner/work/dune/dune/_opam/bin
 binary x86_64-solo5-none-static-cc: found in /home/runner/work/dune/dune/_opam/bin
 binary ocamlopt: found in /home/runner/work/dune/dune/_opam/bin
-checking compilation with x86_64-solo5-none-static-cc -I/home/runner/work/dune/dune/_opam/solo5-sysroot/include/nolibc/ -include _solo5/overrides.h -O2 -fno-strict-aliasing -fwrapv -I/home/runner/work/dune/dune/mirage/_build/solo5/duniverse/Zarith/../../../install/solo5/lib/gmp/: working
+checking compilation with x86_64-solo5-none-static-cc -I/home/runner/work/dune/dune/_opam/solo5-sysroot/include/nolibc/ -include _solo5/overrides.h -O2 -fno-strict-aliasing -fwrapv -I/home/runner/work/dune/dune/mirage/_build/solo5/duniverse/Zarith/../../../install/default/lib/gmp/: working
 include caml/mlvalues.h: found
 library dynlink.cmxa: found
 binary ocamlfind: found in /home/runner/work/dune/dune/_opam/bin

[emillon]

I think that the crux of the issue is that in this dune file:

(rule
 (target gmp.true)
 (deps
  (:exe configure_env.exe)
  %{lib:gmp:libgmp.a}
  %{lib:gmp:libgmp.so}
  %{lib:gmp:gmp.h})
 (action
  (with-stdout-to
   %{target}
   (run %{exe} --cc "%{cc}" --with-gmp=%{lib:gmp:libgmp.a}))))

We resolve %{lib:gmp:libgmp.a} in a different context:

-$ (cd _build/solo5/duniverse/Zarith && ../../../default/duniverse/Zarith/configure_env.exe --cc 'x86_64-solo5-none-static-cc -I/tmp/repro/_opam/solo5-sysroot/include/nolibc/ -include _solo5/overrides.h -O2 -fno-strict-aliasing -fwrapv' --with-gmp=../../../install/solo5/lib/gmp/libgmp.a) > _build/solo5/duniverse/Zarith/gmp.true
+$ (cd _build/solo5/duniverse/Zarith && ../../../default/duniverse/Zarith/configure_env.exe --cc 'x86_64-solo5-none-static-cc -I/tmp/repro/_opam/solo5-sysroot/include/nolibc/ -include _solo5/overrides.h -O2 -fno-strict-aliasing -fwrapv' --with-gmp=../../../install/default/lib/gmp/libgmp.a) > _build/solo5/duniverse/Zarith/gmp.true

[emillon]

Repro in #9200