RFE: build libasmrun_shared too

[vicuna]

Original bug ID: 6693
Reporter: Richard Jones
Assigned to: @gasche
Status: closed (set by @xavierleroy on 2017-02-16T14:15:13Z)
Resolution: fixed
Priority: normal
Severity: minor
Platform: amd64
OS: Linux
Target version: 4.02.2+dev / +rc1
Fixed in version: 4.02.2+dev / +rc1
Category: runtime system and C interface
Tags: patch
Related to: #6733 #6845
Monitored by: @whitequark @gasche @ygrek @hcarty

Bug description

I want to routinely build Linux .so files containing OCaml code. This can be done, see Gerd's instructions here:

http://www.camlcity.org/knowledge/kb_002_shared_library.html

but it requires that you recompile OCaml with -fPIC, otherwise you get this error:

/usr/bin/ld: /usr/lib64/ocaml/libasmrun.a(startup.o): relocation R_X86_64_32 against `.rodata.str1.1' can not be used when making a shared object; recompile with -fPIC

So it would be nice if this just worked out of the box. I think by analogy to libcamlrun_shared.so, there should be libasmrun_shared.so, and ocamlopt should select '-lasmrun_shared' when asked to build a .so file.

This has been requested multiple times on the mailing list:

http://caml.inria.fr/pub/ml-archives/caml-list/2009/12/19e3dc20e585bd216f200789cbea922a.en.html
https://groups.google.com/d/topic/fa.caml/T6blKLDFDog/discussion
http://caml.inria.fr/pub/ml-archives/caml-list/2009/12/7a299d294aa5b8152ce26a18eb03a2dc.en.html

File attachments

• camlrun_pic.patch
• grel.patch

[vicuna]

Comment author: @yallop

I agree that this would be useful. Ctypes provides facilities for building shared objects from OCaml libraries, and it'd be better if the instructions for doing so didn't have to begin with "First, recompile OCaml with -fPIC" ...

Example here:

https://github.com/yallop/ocaml-ctypes-inverted-stubs-example/

[vicuna]

Comment author: Richard Jones

My specific need stems from writing nbdkit plugins in OCaml:

libguestfs/nbdkit@e3abac4

[vicuna]

Comment author: @mshinwell

We must sort this out. I will see what I can do.

[vicuna]

Comment author: @whitequark

I've attached a patch that builds libasmrun_shared.so like libcamlrun_shared.so. It also builds libasmrun_pic.a and libcamlrun_pic.a, since in many cases it is inconvenient to refer to a shared library that is not in default library search path.

[vicuna]

Comment author: @gasche

Would the "people that know this stuff" give an opinion on the proposed patch? It's a dependency to get the ocamlbuild-related patch in #6733 (which I'm ready to merge) to work properly.

[vicuna]

Comment author: @mshinwell

I will have a look at it, when I can find a moment...

[vicuna]

Comment author: @whitequark

Ping? This is needed for #6733...

[vicuna]

Comment author: @mshinwell

I had a look for two minutes, and I spotted two things.

1. It appears that PICFLAGS does not include -O. Is this intentional?

2. Why does e.g. the implicit rule for %.pic.o include ASPPPROFFLAGS? Those are for profiling. (Should we build shared library versions of the profiling-enabled libraries too? I tend to think that there's no point for Linux since perf is almost certainly more useful than gprof---but for other platforms, this argument may not hold.)

[vicuna]

Comment author: @whitequark

1. -O added.
2. ASPPPROFFLAGS removed.

I think we can add profiling-enabled shared libraries when someone needs them.

[vicuna]

Comment author: @whitequark

Ping?

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Comment author: @mshinwell

Pong. (I will look at this when I have a moment.)

[vicuna]

Comment author: @whitequark

Ping?

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Comment author: @avsm

A minor nit on this patch; SHARED is quite a general variable name to go in the top-level Makefile. Would something like SHARED_LIBS or SHARED_LIBS_MODE to reflect the purpose of the variable be clearer?

[vicuna]

Comment author: @gasche

The patch is slightly wrong as there are dangling ; fi in the byterun/Makefile:install-shared target, but that is easy to fix.

[vicuna]

Comment author: @gasche

There was another minor problem with the patch:
libcamlrun_pic.a: $(OBJS)
should be
libcamlrun_pic.a: $(PICOBJS)