[LLVMdev] Question about usage of LLVMLinkModules()

[Lefteris Karapetsas]

Hello Duncan,

Thank you for your reply. I did figure it out in the end. It was a linkage
conflict between the modules. There were some global types that I was
declaring in both modules. After removing them, linking worked perfectly.

Still it's a mystery why I got no error string pointing me to the reason
the linking failed in the first place.

Best Regards,

Lefteris(Eleftherios) Karapetsas  Click here <http://lefteris.refu.co> for
my CV/portfolio website
<http://lefteris.refu.co>   Also maintain a blog <http://blog.refu.co>on
various topics, mostly engineering


On Thu, Jun 11, 2015 at 6:41 PM, Duncan P. N. Exon Smith <
dexonsmith at apple.com> wrote:

>
> > On 2015-Jun-08, at 07:11, Lefteris Karapetsas <lefteris at refu.co> wrote:
> >
> > Hello all,
> >
> > I am using llvm as a backend to a hobby language I am making.  I have
> experimented with the C bindings since the project is written in C. I had
> no problems building a single lllvm module so far. I am not using a JIT
> compiler but at least at the moment am simply generating executables. The
> workflow I am using is to build a module with LLVMModuleCreateWithName()
> and populate it with the LLVMBuilder.
> >
> > After everything is in the module I simply output it into a file with
> LLVMPrintModuleToFile(). Then I am calling llc to convert the IR  to native
> machine code and finally gcc to create an executable out of it. All these
> from inside my program. It may not be the best way to generate an
> executable and I would really welcome as much advice as you can give me on
> that but it works.
> >
> > The issue comes when I actually create 2 different modules. One being a
> "standard" library of sorts and the other the main module which should use
> it. I create both modules, with no errors appearing if I use
> LLVMVerifyModule() on them.
> >
> > The problem is how do I link them? I tried to do it like this:
> >
> >             // if an error occurs LLVMLinkModules() returns true
> >             if (true == LLVMLinkModules(main_module, stdlib_module,
> LLVMLinkerDestroySource, &error)) {
> >                 bllvm_error("Could not link LLVM modules", error);
> >                 goto end;
> >             }
> >
> >
> > But this fails (returns true), with no error. Even though both modules
> are valid. I understand that the above may be a really naive mistake, and
> that my whole approach may be wrong. This is why I would appreciate any
> links to tutorials/documents which would show the proper way to link 2
> modules or some good old simple advice tips from any of you guys.
>
> Weird that you're not getting an error message.
>
> Best thing is probably to spin up a debugger (or add some printfs)
> and see what's going on.
>
> One hypothetical point of failure: module linking requires that both
> modules are in the same context.  If that's not the problem (and it
> probably isn't, since I'd expect crashes there), my bet would be on
> some sort of linkage conflict between the modules.
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