Using __sync_* builtins within libgcc code

[Paolo Carlini]

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'
>
> so clearly I'm not getting this symbol included correctly when I 
> build. Any advice would be appreciated.
Isn't this the well know, annoying, issue that the default 
sub-architecture is i386 and the builtins are only available on i486 and 
later?

Maybe you can usefully exploit the recently added 
__GCC_HAVE_SYNC_COMPARE_AND_SWAP_* macros or add a few more along the 
same way...

Paolo.