[LLVMdev] Assertion in the linker on Mac OS X

Jacob Carlborg doob at me.com
Sat May 11 05:12:56 PDT 2013

This post might be a bit off topic but I'm hoping there's someone here 
that can help me.

I'm working on implementing support for the Objective-C ABI in the D 
programing language. I've based my work on the work made by another 
developer a couple of years ago. Most of the code is already in place 
and I'm now trying to make sure everything works after the merging the 
latest changes from the D compiler.

The problem I have is when linking some code that calls an Objective-C 
method. As far as I understand the object file is supposed to contain a 
section __message_refs, in the __OBJC segment. This section contains 
pointers to C strings, which contain the names of the Objective-C 
selectors (methods). The C strings are stored in the __cstring __TEXT 
section and segment. As far as I can see the these sections looks to 
have the correct flags and contents.

The problem is I'm getting an assertion in the linker:


Line 5024, in Objc1ClassReferences<A>::targetCString. I'm pretty sure 
that the value of "fit->binding" should be 
"ld::Fixup::bindingByContentBound" but instead it is 
"ld::Fixup::bindingDirectlyBound". The definition of these enums are 
located here:


Line 358, in Fixup::TargetBinding.

This is the result of "dumpobj", a tool shipped with the D compiler, on 
the D object file that fails to link:


This is the dump of a corresponding Objective-C object file:


The following is a dump using a pre compiled alpha release of the D 
compiler that the developer I'm basing my work on released in 2011. This 
does not have this problem:


I'm running Mac OS X 10.8.3. All code is compiled as 32bit.

/Jacob Carlborg

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