0004847: callback from C to CAML

Notes
(0005050) daweil (reporter) 2009-08-18 17:47 edited on: 2009-08-18 17:49	NB : I put the issue in the wrong category, it is not a feature request but a blocking issue for migrating our software from 3.10 to 3.11

(0005051) frisch (developer) 2009-08-18 22:31	You'd better use flexlink to produce the main program. You also need to link advapi32.lib and ws2_32.lib. Here is a working Makefile: include $(shell ocamlc -where)/Makefile.config byte: ocamlc -output-obj -o modcaml.obj mod.ml ocamlc -c modwrap.c ocamlc -c main.c $(MKEXE) -o main.exe modwrap.obj main.obj modcaml.obj $(PREFIX)/lib/libcamlrun.lib $(BYTECCLIBS) opt: ocamlopt -output-obj -o modcaml.obj mod.ml ocamlopt -c modwrap.c ocamlopt -c main.c $(MKEXE) -o main.exe modwrap.obj main.obj modcaml.obj $(PREFIX)/lib/libasmrun.lib $(NATIVECCLIBS)

(0005052) daweil (reporter) 2009-08-19 09:25	Thanks for your fast answer. Now I want to do the next step that is required for our software : callback from C to CAML but but the CAML in a DLL. (in ocaml3.10, I had to patch the caml sources to do it, but it seems that I should not need thispatch anymore in pcaml3.11) So I added the following target in the makefile you suggest : FLEXOPT= -show-exports -show-imports bytedll: ocamlc -output-obj -o modcaml.obj mod.ml ocamlc -c modwrap.c ocamlc -c main.c $(MKDLL) $(FLEXOPT) -implib -o libmodwrap.dll modwrap.obj modcaml.obj $(PREFIX)/lib/libcamlrun.lib $(BYTECCLIBS) $(MKEXE) $(FLEXOPT) -o main.exe main.obj libmodwrap.lib ws2_32.lib advapi32.lib It fails with the following message : ** Cannot resolve symbols for main.obj: _caml_startup _fib _format_result What's wrong ? The symbols "_caml_startup _fib _format_result" appears to be exporteed when I use the -show_exports option of flexlink

(0005053) frisch (developer) 2009-08-19 14:14	The symbols are exported in the sense of flexdll. Since the DLL will be loaded in the main program directly (not with flexdll), through its import library, you need real DLL exports. You can achieve that by passing /def:XXX flags to the linker, or with a .def file, or by adding declspec(dllexport) directives to modwrap.c. For the .def file solution, you can create a file modwrap.def with those lines: EXPORTS caml_startup fib format_result And then the Makefile rule would be: bytedll: ocamlc -c modwrap.c ocamlc -cclib "-implib -link /def:modwrap.def" -output-obj -o libmodwrap.dll modwrap.obj mod.ml ocamlc -c main.c $(MKEXE) -o main.exe main.obj libmodwrap.lib Note that I use here the new feature of OCaml that allows you to get a DLL directly (-output-obj X.dll).

(0005057) daweil (reporter) 2009-08-19 16:27 edited on: 2009-08-19 16:29	Thanks for your answer. I'm making progress. I'm able to make a dll containing caml code compiled in byte & native mode and link a main file to the .lib file exporting the symbols I want. Note that I put the wrapper outside the dll, it corresponds to the use case I have. Now, I would like to understand the other method which use flexdll to dynamically load my dll. I manage to compile but execution fails : ./mainflex.exe No master relocation table make: *** [byteflexdll] Error 1 Can you explain what happen? Unzip caml_from_c_main_with_flexdll.zip to reproduce the issue.

(0005058) frisch (developer) 2009-08-19 21:12	Flexlink can really produce two very different kinds of DLLs: - regular DLLs, which correspond to "main program" linked as a DLL (that, they are in charge of performing the relocation for other DLLs loaded by flexlink) and can be loaded in normal ways (either explicit with LoadLibrary or through their import library); - flexlink DLLs, which need to be loaded by flexdll_dlopen. The "-output-obj X.dll" feature of OCaml produces a regular DLL. If you want to produce a flexlink DLL, you need to produce the .obj yourself and use flexlink explictly. Also, since mainflex.c does not refer to OCaml headers, it seems better to call the C compiler directly. Here is a working Makefile, for both bytecode and native: byteflexdll: ocamlc -output-obj -o modcaml.obj mod.ml ocamlc -c modwrap.c $(MKDLL) -o libmodwrap.dll modwrap.obj modcaml.obj $(PREFIX)/lib/libcamlrun.lib $(BYTECCLIBS) cl /MD /nologo /c -I "$(shell flexlink -where)" mainflex.c $(MKEXE) $(FLEXOPT) -o mainflex.exe mainflex.obj ./mainflex.exe optflexdll: ocamlopt -output-obj -o modcaml.obj mod.ml ocamlc -c modwrap.c $(MKDLL) -o libmodwrap.dll modwrap.obj modcaml.obj $(PREFIX)/lib/libasmrun.lib $(BYTECCLIBS) cl /MD /nologo /c -I "$(shell flexlink -where)" mainflex.c $(MKEXE) $(FLEXOPT) -o mainflex.exe mainflex.obj ./mainflex.exe

(0005061) daweil (reporter) 2009-08-24 16:31	Thanks. All these examples works fine. I think you can close the issue. Will this makefile be include in the official caml documentation?

(0005110) daweil (reporter) 2009-09-18 10:20	It doesn't work on Windows 64bits. I found 2 issues. 1) ocamlc -output-obj fails with the message "ocamlc -output-obj -o modcaml.obj mod.ml modcaml.c modcaml.c(2465) : error C2371: 'caml_get_public_method' : redefinition; different basic types C:/ProgramFiles/ocaml-3.11.1win64VC8/lib\caml/mlvalues.h(190) : see declaration of 'caml_get_public_method' modcaml.c(2721) : warning C4133: 'initializing' : incompatible types - from 'value (__cdecl )(value,value)' to 'primitive' File "mod.ml", line 1, characters 0-1: Error: Error while building custom runtime system " 2) I cannot use flexlink together with /DEBUG link option if I want to debug by main program: "flexlink -x64 -merge-manifest -exe -o main_opt.exe modwrap.obj main.obj libmodwrap.lib -link "/DEBUG" flexdll_msvc.obj : fatal error LNK1103: debugging information corrupt; recompile module * Fatal error: Error during linking"

(0005114) frisch (developer) 2009-09-18 22:50	I won't be able to look at (1) in the next two weeks. For (2), it is indeed the case that flexlink does not support COFF debugging information and there is little chance that it will be implemented (by myself).

(0005116) daweil (reporter) 2009-09-23 15:10	All these issues are only on 64 machines. For 2), the problem may be that I don't use the same version of compiler, so I should try again to recompile flexlink myself (I tried a few weeks ago but failed)

(0005117) xleroy (administrator) 2009-09-23 16:32	I looked into (1) and I think I've diagnosed and fixed the problem. Still needs to be tested under Win64. Fix will go in 3.11.2.

Issue History
Date Modified	Username	Field	Change
2009-08-18 17:43	daweil	New Issue
2009-08-18 17:43	daweil	File Added: caml_from_c.zip
2009-08-18 17:47	daweil	Note Added: 0005050
2009-08-18 17:49	daweil	Note Edited: 0005050
2009-08-18 17:49	daweil	Note Edited: 0005050
2009-08-18 22:31	frisch	Note Added: 0005051
2009-08-18 22:31	frisch	Status	new => assigned
2009-08-18 22:31	frisch	Assigned To	=> frisch
2009-08-18 22:31	frisch	Status	assigned => resolved
2009-08-18 22:31	frisch	Resolution	open => fixed
2009-08-19 09:25	daweil	Note Added: 0005052
2009-08-19 09:25	daweil	Status	resolved => feedback
2009-08-19 09:25	daweil	Resolution	fixed => reopened
2009-08-19 11:14	doligez	Severity	feature => major
2009-08-19 14:14	frisch	Note Added: 0005053
2009-08-19 16:27	daweil	Note Added: 0005057
2009-08-19 16:28	daweil	File Added: caml_from_c_main_with_flexdll.zip
2009-08-19 16:29	daweil	Note Edited: 0005057
2009-08-19 21:12	frisch	Note Added: 0005058
2009-08-24 16:31	daweil	Note Added: 0005061
2009-08-27 10:31	frisch	Status	feedback => resolved
2009-08-27 10:31	frisch	Resolution	reopened => fixed
2009-09-18 10:20	daweil	Note Added: 0005110
2009-09-18 10:20	daweil	Status	resolved => feedback
2009-09-18 10:20	daweil	Resolution	fixed => reopened
2009-09-18 22:50	frisch	Note Added: 0005114
2009-09-23 15:10	daweil	Note Added: 0005116
2009-09-23 16:32	xleroy	Note Added: 0005117
2009-09-23 16:33	xleroy	Status	feedback => resolved
2009-09-23 16:33	xleroy	Resolution	reopened => fixed
2009-09-23 16:33	xleroy	Fixed in Version	=> 3.11.2+dev
2011-05-29 12:20	xleroy	Status	resolved => closed

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