[LLVMdev] ocaml build system

[Nick Lewycky]

Gordon Henriksen wrote:
> On 2009-01-19, at 13:50, Nick Lewycky wrote:
> 
>> I have an issue with the OCaml build system and the ExecutionEngine.
>>
>> PR2128 has a patch to change the Interpreter to use libffi. This 
>> breaks test/Bindings/Ocaml/executionengine.ml because OCaml doesn't 
>> try to link with libffi, even though llvm-config knows that we should:
>>
>>  $ Debug/bin/llvm-config --ldflags interpreter
>>  -L/home/nicholas/llvm-commit/Debug/lib  -lpthread -lffi -ldl -lm -lelf
>>
>> If I run 'ocamlc' by hand and pass it '-cclib -lffi', the test 
>> succeeds, so this is the only remaining problem. Is anyone familiar 
>> with how Ocaml knows what libraries to link against? We can't just 
>> pass `llvm-config --ldflags interpreter` to ocamlc because it doesn't 
>> support the -L argument.
>>
>> Does anyone have any ideas how this ought to work?
> 
> The linker flags for each .cma (ocaml library) are baked in by ocaml. 
> Here's the relevant section from Makefile.ocaml:
> 
>     # Info from llvm-config and similar
>     ifdef UsedComponents
>     UsedLibs = $(shell $(LLVM_CONFIG) --libs $(UsedComponents))
>     UsedLibNames = $(shell $(LLVM_CONFIG) --libnames $(UsedComponents))
>     endif
> 
>     # Tools
>     OCAMLCFLAGS += -I $(OcamlDir) -I $(ObjDir)
>     ifneq ($(ObjectsO),)
>     OCAMLAFLAGS += $(patsubst %,-cclib %, \
>                      $(filter-out -L$(LibDir),-l$(LIBRARYNAME) \
>                                               $(shell $(LLVM_CONFIG)
>     --ldflags)) \
>                                               $(UsedLibs))
>     else
>     OCAMLAFLAGS += $(patsubst %,-cclib %, \
>                      $(filter-out -L$(LibDir),$(shell $(LLVM_CONFIG)
>     --ldflags)) \
>                                               $(UsedLibs))
>     endif
> 
> 
> This transforms "x y z" from llvm-config into "-cclib x -cclib y -cclib 
> z", which instructs ocaml to pass "x y z" down to the linker when 
> creating an executable. The UsedComponents variable originates in this 
> case from bindings/ocaml/executionengine/Makefile:
> 
>     LEVEL := ../../..
>     LIBRARYNAME := llvm_executionengine
>     DONT_BUILD_RELINKED := 1
>     * UsedComponents := executionengine jit interpreter native *
>     UsedOcamlInterfaces := llvm llvm_target
> 
>     include ../Makefile.ocaml
> 
> 
> I don't see anything obviously wrong here; it seems that llvm-config 
> -ldflags executionengine jit interpreter native  should be invoked, 
> which should give you the -cclib -lffi you seek.  make VERBOSE=1  and/or 
> TOO_VERBOSE=1 should show you the full ocaml command lines; maybe 
> that'll show where -lffi is getting dropped on the floor.

Thanks for the explanation. It looks like what really happened is that 
the .cma files weren't regenerated when llvm-config changed. After 
refreshing bindings/ocaml and rebuilding LLVM, the test passes.

Nick

> — Gordon
> 
> 
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