[llvm-commits] [llvm] r78872 - /llvm/trunk/lib/Target/X86/AsmPrinter/X86ATTAsmPrinter.cpp

[Chris Lattner]

On Aug 23, 2009, at 2:10 PM, Chris Lattner wrote:

>
> On Aug 23, 2009, at 12:01 PM, Nick Kledzik wrote:
>
>>>>
>>>> I suppose.  There are some in the gcc testsuite.  I was asked not  
>>>> to run it anymore but somebody should be; it's the best tests we  
>>>> have for ObjC metadata.
>>>>
>>>>> Do ppc/arm need a similar fix?
>>>>
>>>> Probably, good catch, I'll look at it.
>>>>
>>>
>>> I still don't understand what this is doing.  "l" labels are not  
>>> visible outside of their translation unit. Why could they possibly  
>>> need to be marked as weak definitions?  They can't be overridden  
>>> by other translation units, so it doesn't make sense (to me) for  
>>> them to have to be weak.
>>
>> Chris, it is 'L' labels that are visible on in their translation  
>> unit.  'l' labels are visible throughout the linkage unit.   Making  
>> these weak-hidden enables the linker to coalesce duplicates.
>
> Aha, that makes perfect sense.  I'll update the documentation.   
> Thanks Nick.

Actually, one more question Nick :).

I was going to update the docs to say:

   <dt><tt><b><a name="linkage_linker_private">linker_private</a></b></ 
tt>: </dt>
   <dd>Similar to private, but the symbol is passed through the  
assembler and
       removed by the linker after evaluation.  Note that (unlike  
private
       symbols) linker_private symbols are subject to coalescing by  
the linker:
       weak symbols get merged and redefinitions are rejected.   
However, unlike
       normal strong symbols, they are removed by the linker from the  
final
       linked image (executable or dynamic library).</dd>

However, it looks like the linker doesn't reject two .o files that  
contain redefinitions of the same label with either -r or -dylib.  I  
tried linking together two .o files that contained this .s file:

lFoo:
   .byte 1

Shouldn't I get a redefinition error?  Is the weak merging semantics  
just a special case magic behavior that is unlike normal strong symbols?

-Chris