More information in ocamlc -config

[vicuna]

Original bug ID: 7172
Reporter: @dbuenzli
Assigned to: @dra27
Status: assigned (set by @mshinwell on 2016-12-14T11:38:40Z)
Resolution: open
Priority: normal
Severity: feature
Version: 4.02.3
Target version: 4.07.0+dev/beta2/rc1/rc2
Category: configure and build/install
Monitored by: @gasche @diml @dbuenzli

Bug description

It would be nice if ocamlc -config could report whether:

1. Native compilation is available
2. Native dynlinking is available.

[vicuna]

Comment author: @mshinwell

I think we may need to fix matters for 4.03 such that there is a means of discovering whether Flambda is enabled or not. Perhaps we could just fix these all at once.

[vicuna]

Comment author: @dbuenzli

@shinwell I'd be delighted if this could go into 4.03 and I may be tempted to hide the fact that ocamlc -config already reports if flambda is enabled or not.

[vicuna]

Comment author: @mshinwell

Oh, so it does. Well it will probably have to wait then :p

[vicuna]

Comment author: @dbuenzli

Grrrrr.

[vicuna]

Comment author: @dbuenzli

Somehow I had hoped that I could fill the missing slots with:

$(ocamlc -where)/Makefile.config

but in fact this file seems to reflect the output of the configure process, not of what is actually installed, e.g. on a bytecode only switch like:

https://github.com/ocaml/opam-repository/blob/master/compilers/4.02.3/4.02.3%2Bbytecode-only/4.02.3%2Bbytecode-only.comp

NATDYNLINK will be true even though there no actual dynlink.cmxa. In fact reading the INSTALL file it seems there's no way to configure ocaml to be bytecode only.

So I guess I'm left with discovery hacks.

I'm thinking about:

• native code compilation is available if $(ocamlc -where)/libasmrun.$(EXT_DLL) exists
  (looking up ocamlopt in the path can be a bit unreliable, for example in a bytecode only switch ocamlopt may actually be in the path, but it's the ocamlopt of the system compiler...)

• native dynlinking is available if $(ocamlc -where)/dynlink.cmxa exists

Does it sound reasonable ?

[vicuna]

Comment author: @dbuenzli

That is libasmrun.$(EXT_LIB) rather than $(EXT_DLL).

[vicuna]

Comment author: @gasche

I needed a -no-native-compiler configure option to test the bytecode-only build of ocamlbuild, and added it to the script in #387. The relevant variables should be set to a meaningful value in this case, and the fact that this is not done for NATDYNLINK comes from an (independent) omission in the relevant logic:

https://github.com/ocaml/ocaml/blob/d3d30f3/configure#L874-L878

I need to document the -no-native-compiler switch in the INSTALL file, and I think I will fix the configure script as well.

[vicuna]

Comment author: @dbuenzli

Also it would be nice to give us ext_exe, since the logic is a little bit twisted and requires to consult both ccomp_type and os_type. There is the EXE variable in Makefile.config but I now decided I'd rely only on the output of ocamlc -config.

[vicuna]

Comment author: @damiendoligez

@dbuenzli your "discovery hacks" look quite reasonable to me.

It's not clear to me how ocamlc -config could know whether the native compiler was built or anything about the build process. Currently, it relies only on information from configure.

I agree with ext_exe.

[vicuna]

Comment author: @dbuenzli

@doligez The solution is to be able to specify whether native compilers should be built in the configure of course.

[vicuna]

Comment author: @gasche

I proposed
#513
to solve this issue.

[vicuna]

Comment author: @gasche

#513 has just been merged in 4.03 and trunk. ./configure -no-native-compiler now sets NATDYNLINK=false in Makefile.config.

[vicuna]

Comment author: @dbuenzli

Another bit that is useful for build systems to know an that should be reported by ocamlc -config is the value of Sys.word_size on the target platform. This is useful even for OCaml programs as it affects the size of ocaml integers.

Currently workarounds include:

1. Grepping for SIZEOF_PTR in $(ocamlc -where)/caml/config.h
2. Trying to pattern match on the values of architecture: and model: of ocamlc -config and try to infer the size based on the meaning of these keys according to

   ocaml/configure

   Lines 810 to 862 in 4ca0ca4

   	case "$target" in
   	sparc*-*-solaris2.*) arch=sparc; system=solaris;;
   	sparc*-*-*bsd*) arch=sparc; system=bsd;;
   	sparc*-*-linux*) arch=sparc; system=linux;;
   	sparc*-*-gnu*) arch=sparc; system=gnu;;
   	i[3456]86-*-linux*) arch=i386; system=linux_`sh ./runtest elf.c`;;
   	i[3456]86-*-*bsd*) arch=i386; system=bsd_`sh ./runtest elf.c`;;
   	i[3456]86-*-nextstep*) arch=i386; system=nextstep;;
   	i[3456]86-*-solaris*) if $arch64; then
   	arch=amd64; system=solaris
   	else
   	arch=i386; system=solaris
   	fi;;
   	i[3456]86-*-haiku*) arch=i386; system=beos;;
   	i[3456]86-*-beos*) arch=i386; system=beos;;
   	i[3456]86-*-cygwin*) arch=i386; system=cygwin;;
   	i[3456]86-*-darwin*) if $arch64; then
   	arch=amd64; system=macosx
   	else
   	arch=i386; system=macosx
   	fi;;
   	i[3456]86-*-gnu*) arch=i386; system=gnu;;
   	i[3456]86-*-mingw*) arch=i386; system=mingw;;
   	powerpc64le*-*-linux*) arch=power; model=ppc64le; system=elf;;
   	powerpc*-*-linux*) arch=power;
   	if $arch64; then model=ppc64; else model=ppc; fi
   	system=elf;;
   	powerpc-*-netbsd*) arch=power; model=ppc; system=elf;;
   	powerpc-*-openbsd*) arch=power; model=ppc; system=bsd_elf;;
   	s390x*-*-linux*) arch=s390x; model=z10; system=elf;;
   	armv6*-*-linux-gnueabihf) arch=arm; model=armv6; system=linux_eabihf;;
   	arm*-*-linux-gnueabihf) arch=arm; system=linux_eabihf;;
   	armv7*-*-linux-gnueabi) arch=arm; model=armv7; system=linux_eabi;;
   	armv6t2*-*-linux-gnueabi) arch=arm; model=armv6t2; system=linux_eabi;;
   	armv6*-*-linux-gnueabi) arch=arm; model=armv6; system=linux_eabi;;
   	armv6*-*-freebsd*) arch=arm; model=armv6; system=freebsd;;
   	earmv6*-*-netbsd*) arch=arm; model=armv6; system=netbsd;;
   	earmv7*-*-netbsd*) arch=arm; model=armv7; system=netbsd;;
   	armv5te*-*-linux-gnueabi) arch=arm; model=armv5te; system=linux_eabi;;
   	armv5*-*-linux-gnueabi) arch=arm; model=armv5; system=linux_eabi;;
   	arm*-*-linux-gnueabi) arch=arm; system=linux_eabi;;
   	arm*-*-openbsd*) arch=arm; system=bsd;;
   	zaurus*-*-openbsd*) arch=arm; system=bsd;;
   	x86_64-*-linux*) arch=amd64; system=linux;;
   	x86_64-*-gnu*) arch=amd64; system=gnu;;
   	x86_64-*-freebsd*) arch=amd64; system=freebsd;;
   	x86_64-*-netbsd*) arch=amd64; system=netbsd;;
   	x86_64-*-openbsd*) arch=amd64; system=openbsd;;
   	x86_64-*-darwin*) arch=amd64; system=macosx;;
   	x86_64-*-mingw*) arch=amd64; system=mingw;;
   	aarch64-*-linux*) arch=arm64; system=linux;;
   	x86_64-*-cygwin*) arch=amd64; system=cygwin;;
   	esac

[vicuna]

Comment author: @dbuenzli

shinwell asked me to update on the status of this bug. So in 4.04, ocamlc -config still does not report the following useful tidbits:

• ext_exe
• word_size
• natdynlink
• nativecomp

[vicuna]

Comment author: @gasche

#970