[LLVMdev] Error with apple's linker

[Nick Kledzik]

Background:
In Mac OS X 10.5 and later, OS dylibs are copied into something called  
the dyld shared cache.  In the cache all the dylibs are bound to one  
another, which improves launch time of all processes.  The shared  
cache has a funny constraint where all read-only pages need to be  
continuous.  This requirement means the __TEXT and __DATA segments of  
each dylib need to be split apart.  The normal PIC codegen uses pc- 
relative access from code to data, so all those pc-relative addresses  
need to be altered when a dylib is incorporated into the dyld shared  
cache.  To facilitate that, the linker adds content to each dylib that  
describes where all the code-to-data references are.

The "double split seg info" error means the linker ran into some case  
where it does not now how to encode a code-to-data reference.  In  
particular is seems like there is two relocations on the same address??

If you have a test case that reproduces this, I can isolate exactly  
which instruction in the code is causing the problem.

-Nick
Mac OS X Linker


On Aug 11, 2009, at 1:12 AM, Nicolas Geoffray wrote:
> Hi all,
>
> I'm having an issue with the ld linker on MacOSX (10.5). I have
> generated a large .s file with llc and the relocation-model=pic
> argument. When I ask the linker to create the .dylib file, I get  
> this error:
>
> ld: double split seg info for same address
> collect2: ld returned 1 exit status
>
> The generated .s file for Linux works fine with Linux's ld linker. If
> anyone has an idea of what's happening with apple's ld, I'd be happy  
> to
> hear it.
>
>
> Here's the full context:
> With VMKit's compiler, I create a .bc file of the standard Java  
> library.
> I then run the -std-compile-opts optimizations, so the .bc file passes
> verification. I generate the .s file with the following command line:
>
> llc -relocation-model=pic -disable-fp-elim myfile.bc
>
> Finally, I use LLVM's Makefile machinery to create a .dylib file from
> the .s file.
>
> Cheers,
> Nicolas
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