Dune compilation with -output-obj

Ecosystem
,
1

Here is my dune file:

(executable
 (name binding)
 (modules binding)
 (libraries xxx)
 (modes
  (native object))
 ;(ocamlopt_flags (-output-obj))
 (promote
  (until-clean)
  (into .)))

This compiles, but doesn’t work later in my process.

The problem is that line

Running[3]: (cd _build/default && /home/xo/.opam/5.1.1/bin/ocamlopt.opt -w @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40 -strict-sequence -strict-formats -short-paths -keep-locs -g -o binding.exe.o -output-complete-obj /home/xo/.opam/5.1.1/lib/xxx/xxx.cmxa .binding.eobjs/native/dune__exe__Binding.cmx)

I need to change the -output-complete-obj into -output-obj for it to work.
(I build the .so later in my process)

About my attempts:

  • The commented line doesn’t work as the .cmx compilation needs the flag out
  • Just in case, the -output-complete-obj version fails on next step because I need a -fPIC version (which I link with libasmrun_pic.a as a matter of fact) Maybe there’s another workaround considering that…

Also, for reference, my working compilation line I want to reproduce in dune is:

opam exec -- ocamlfind ocamlopt -package xxx -linkpkg -output-obj -o binding.o binding.ml
2

Dune does not support -output-obj unfortunately. Your only hope is to write a rule by hand to produce what you need, but I never tried myself so am not sure how complicated it is.

Cheers,
Nicolas

3

This may be nothing to do with your problem (the issues were different from the ones you report), but to get dune’s (native object) mode to work in a toy project of my own I had to compile with the -noautolink flag which in turn required explicitly linking with libunixnat.a, libthreadnat.a and liblwt_unix_stubs.a.

As I say it was a toy project and I didn’t spend much time looking at what the problem was, but I ended with a flags field in the dune file comprising (flags :standard -noautolink -cclib -lunixnat -cclib -lthreadsnat -cclib -llwt_unix_stubs). With that I could get my simple project to compile and run. YMMV.

4

See also this comment.

5

Thank you for the comments. Unfortunately the flags option doesn’t do the trick :frowning_face:

I found out how to write a rule and copy-paste my compilation line. Not that difficult, however, I might as well just write a Makefile then :roll_eyes: (looks cleaner)

Last option which just worked: add the following line to prevent the error further away. It doesn’t prevent the -output-complete-obj but it seems to do the trick to prevent the errors further ahead.

(link_flags (-cclib -lasmrun_pic))

Now last twist: this option is only necessary on Linux. I found something with enabled_if but that seems to apply on the whole target, not on the option itself (and I don’t want targets with different names according to the OS)