Zarith compilation fails in 32bit OCaml switches on a 64bit host.

[ejgallego]

Ubuntu 18.04, opam 2.0, switch is 4.07.0+32bit:

./configure 
binary ocaml: found in /home/egallego/.opam/4.07.0+32bit/bin
binary ocamlc: found in /home/egallego/.opam/4.07.0+32bit/bin
binary ocamldep: found in /home/egallego/.opam/4.07.0+32bit/bin
binary ocamlmklib: found in /home/egallego/.opam/4.07.0+32bit/bin
binary ocamldoc: found in /home/egallego/.opam/4.07.0+32bit/bin
binary ar: found in /usr/bin
binary perl: found in /usr/bin
binary gcc: found in /usr/bin
binary ocamlopt: found in /home/egallego/.opam/4.07.0+32bit/bin
checking compilation with gcc -O3 -Wall -Wextra : working
include caml/mlvalues.h: found
library dynlink.cmxa: found
binary ocamlfind: found in /home/egallego/.opam/4.07.0+32bit/bin
OCaml's word size is 32
binary uname: found in /bin
include gmp.h: found
library gmp: found
OCaml extended comparison supported
OCaml new hash functions available
OCaml supports -bin-annot to produce documentation

detected configuration:

  native-code:          yes
  dynamic linking:      yes
  asm path:             x86_64
  defines:              -DZ_OCAML_HASH -DZ_OCAML_COMPARE_EXT -DHAS_GMP -DZ_ELF -DZ_DOT_LABEL_PREFIX 
  libraries:             -lgmp
  C options:            -O3 -Wall -Wextra 
  asm options           
  installation path:    /home/egallego/.opam/4.07.0+32bit/lib
  installation method   findlib

$ make
project.mak:151: depend: No existe el archivo o el directorio
./z_pp.pl x86_64
Name "main::extra" used only once: possible typo at ./z_pp.pl line 29.
found assembly file caml_z_x86_64.S
  found abs
  found add
  found div
  found divexact
  found logand
  found lognot
  found logor
  found logxor
  found mul
  found neg
  found pred
  found rem
  found shift_left
  found shift_right
  found sub
  found succ
ocamldep -native  z.ml q.ml big_int_Z.ml z.mli q.mli big_int_Z.mli > depend
ocamlc -I +compiler-libs -bin-annot  -c z.mli
ocamlc -I +compiler-libs -bin-annot  -c z.ml
ocamlc -I +compiler-libs -bin-annot  -c q.mli
ocamlc -I +compiler-libs -bin-annot  -c q.ml
ocamlc -I +compiler-libs -bin-annot  -c big_int_Z.mli
ocamlc -I +compiler-libs -bin-annot  -c big_int_Z.ml
ocamlmklib -failsafe -o zarith z.cmo q.cmo big_int_Z.cmo -lgmp
gcc -DZ_OCAML_HASH -DZ_OCAML_COMPARE_EXT -DHAS_GMP -DZ_ELF -DZ_DOT_LABEL_PREFIX     -c -o caml_z_x86_64.o caml_z_x86_64.S
ocamlc -ccopt "-I/home/egallego/.opam/4.07.0+32bit/lib/ocaml  -DZ_OCAML_HASH -DZ_OCAML_COMPARE_EXT -DHAS_GMP -DZ_ELF -DZ_DOT_LABEL_PREFIX  -O3 -Wall -Wextra " -c caml_z.c
ocamlmklib -failsafe -o zarith caml_z_x86_64.o caml_z.o -lgmp
/usr/bin/ld: la arquitectura i386:x86-64 del fichero de entrada `caml_z_x86_64.o' es incompatible con la salida i386
collect2: error: ld returned 1 exit status
ocamlc -I +compiler-libs -bin-annot  -c zarith_top.ml
ocamlc -o zarith_top.cma -a zarith_top.cmo
ocamlopt -I +compiler-libs  -c z.ml
ocamlopt -I +compiler-libs  -c q.ml
ocamlopt -I +compiler-libs  -c big_int_Z.ml
ocamlmklib -failsafe -o zarith z.cmx q.cmx big_int_Z.cmx -lgmp
ocamlopt -shared -o zarith.cmxs -I . zarith.cmxa -linkall
/usr/bin/ld: se salta el ./libzarith.a incompatible mientras se busca -lzarith
/usr/bin/ld: no se puede encontrar -lzarith
collect2: error: ld returned 1 exit status
File "caml_startup", line 1:
Error: Error during linking
project.mak:79: recipe for target 'zarith.cmxs' failed
make: *** [zarith.cmxs] Error 2

[ejgallego]

./configure -host i686-linux-gnu && make CC='gcc -m32' makes the build work.

I wonder how this should be detected under the 32bit OPAM.

[ejgallego]

I see that a similar https://forge.ocamlcore.org/tracker/?func=detail&atid=1095&aid=1539&group_id=243 report was closed.

Indeed, it may make sense for Zarith not to have to care about incorrect host settings; I have little clue on cross-compilation but then I wonder what the 4.07.0+32bit switch is doing.

Does it make sense to have a 32bit OCaml and not set arch to i686?

[antoinemine]

OK. PR #56 changes slightly the configure to detect this situation (based on the host and actual size of OCaml words).