llvm dev - Dec 2006 - [LLVMdev] [patch] emit .weak for zero initialized weak variables

> I'm not sure this is right.  C code like this:
>
> int X;
>
> should compile to a .comm directive, not a .weak directive, right?
right.

According to GCC, "int  x" should compile to ".comm   x",
but "int x
__attribute__((weak))" should compile to
---------------
.weak   x
x:
        .zero   4
---------------

It looks like we have a bug in llvm-gcc, both C codes compile to
--------------------------
%x = weak global int 0
--------------------------
> -Chris
Best Regards,
Rafael

On Mon, 18 Dec 2006, [UTF-8] Rafael Esp?ndola wrote:
>> I'm not sure this is right.  C code like this:
>>
>> int X;
>>
>> should compile to a .comm directive, not a .weak directive, right?
>
> right.
>
> According to GCC, "int  x" should compile to ".comm  
x", but "int x
> __attribute__((weak))" should compile to
> ---------------
> .weak   x
> x:
>        .zero   4
> ---------------
>
> It looks like we have a bug in llvm-gcc, both C codes compile to
> --------------------------
> %x = weak global int 0
> --------------------------
Is there a semantic difference between the two?  Just because GCC compiles 
them to different things, it doesn't mean they do different things...

-Chris

-- 
http://nondot.org/sabre/
http://llvm.org/

> Is there a semantic difference between the two?  Just because GCC compiles
> them to different things, it doesn't mean they do different things...
Sorry for the long delay...

On a x86 box I am able to use both declarations interchangeably. There
is a  problem if we have both a declaration and an use on the same
file: We must print a ".weak" because of the use, but if we printed a
".comm" for the declaration, the assembler will reject the file:

Error: symbol `a' can not be both weak and common

Best Regards,
Rafael