llvm dev - Jun 2015 - [LLVMdev] Question about usage of LLVMLinkModules()

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.

Thank you for your time.
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
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> 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.

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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Duncan P. N. Exon Smith <dexonsmith <at> apple.com>
writes:
> > 
> > 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.
Not so weird:
http://reviews.llvm.org/D10241

Regards

Antoine.