Using __sync_* builtins within libgcc code

[Luke Dalessandro]

Paolo Carlini wrote:
> Luke Dalessandro wrote:
>> I'm making some modifications to exception handling inside of 
>> unwind-dw2-fde.c that I'd like to use __sync_bool_compare_and_swap 
>> for, unfortunately I can't seem to figure out how to correctly use 
>> builtins in the context of libgcc.
>>
>> I've tried a bunch of different things, but I consistently get the error
>>
>>   bin/../lib/gcc/i686-pc-linux-gnu/4.3.1/../../../libgcc_s.so: 
>> undefined reference to `__sync_bool_compare_and_swap_4'
>>
> Maybe you can usefully exploit the recently added 
> __GCC_HAVE_SYNC_COMPARE_AND_SWAP_* macros or add a few more along the 
> same way...

Thank you Paolo, this allows me to wrap cas in a function that falls back to a 
mutex for targets that don't support builtins.

I was aware of the i386 restriction, but didn't realize that i686-* platforms 
still defaulted to i386.

Thanks for everyone's help.

Luke