llvm dev - May 2011 - [LLVMdev] Difficulty compiling LLVM-based tools with clang

I recently modified my compiler's build files to use clang if it detects its
available, however I'm running into a number of problems with this. I'm
having one set of problems on OS X, and a different set of problems under
Ubuntu.

In both cases I'm attempting to link my frontend - compiled with clang -
against the LLVM libraries - compiled with gcc. (I thought about compiling
LLVM with clang, but then I'd have to compile it twice to bootstrap.)

Under OS X, I get the following error when I try to link:

Undefined symbols:

  "___eprintf", referenced from:

      ___eprintf$non_lazy_ptr in
libLLVMSupport.a(SearchForAddressOfSpecialSymbol.cpp.o)

ld: symbol(s) not found

clang-3: error: linker command failed with exit code 1 (use -v to see
invocation)


As you can see the reference is coming from the LLVM libs.

Under Ubuntu, the problem I get is a crash when calling a method in
DIBuilder. The problem appears to be in the StringRef param, which looks
like it's full of junk when I examine it in the debugger, even though my
code is just passing in the default value for the parameter, which is an
empty StringRef(). I'm guessing there is some incompatibility in the calling
conventions, but I'm passing virtually the same command-line arguments to
clang as I would normally pass to gcc. (With some minor differences having
to do with warning suppression).

-- 
-- Talin
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On 11-05-12 8:33 PM, Talin wrote:
> I recently modified my compiler's build files to use clang if it
detects
> its available, however I'm running into a number of problems with this.
> I'm having one set of problems on OS X, and a different set of problems
> under Ubuntu.
>
> In both cases I'm attempting to link my frontend - compiled with clang
-
> against the LLVM libraries - compiled with gcc. (I thought about
> compiling LLVM with clang, but then I'd have to compile it twice to
> bootstrap.)
>
> Under OS X, I get the following error when I try to link:
>
>     Undefined symbols:
>
>     "___eprintf", referenced from:
>
>            ___eprintf$non_lazy_ptr in
>     libLLVMSupport.a(SearchForAddressOfSpecialSymbol.cpp.o)
>
>     ld: symbol(s) not found
>
>     clang-3: error: linker command failed with exit code 1 (use -v to
>     see invocation)
>
Interesting. A coworker had exactly the same problem trying to build 
rust with clang after having built llvm with gcc.

The problem comes from  SearchForAddressOfSpecialSymbol.cpp:

     // FIXME: Currently disabled when using Clang, as we don't always 
have our
     // runtime support libraries available.
#ifndef __clang__
#ifdef __i386__
     EXPLICIT_SYMBOL(__eprintf);
#endif
#endif

Now, exactly what runtime library is not available is something that 
someone more familiar with OS X will have to answer :-)
> --
> -- Talin
Cheers,
Rafael

On 5/12/11 7:08 PM, Rafael Ávila de Espíndola wrote:
> The problem comes from  SearchForAddressOfSpecialSymbol.cpp:
> 
>      // FIXME: Currently disabled when using Clang, as we don't always 
> have our
>      // runtime support libraries available.
> #ifndef __clang__
> #ifdef __i386__
>      EXPLICIT_SYMBOL(__eprintf);
> #endif
> #endif
> 
> Now, exactly what runtime library is not available is something that 
> someone more familiar with OS X will have to answer :-)
The runtime support library the comment talks about is none other than
compiler-rt. (Specifically, libclang_rt.eprintf.a.) If you check out
compiler-rt into <llvm-src>/projects/compiler-rt, clang will pick it up
and build it automatically.

Chip