Re: Using __sync_* builtins within libgcc code

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Tue, 10 Jun 2008, 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'
> > 
> > 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?

I hold that it is a bug that i686-* tools default to -march=i386 instead 
of -march=i686 (whereas e.g. sparcv9-* tools default to -mcpu=sparcv9, and 
-mcpu means -march for SPARC).  My --with-arch-32 etc. patch 
<http://gcc.gnu.org/ml/gcc-patches/2008-06/msg00124.html> (config/i386 
part pending review) would facilitate fixing this bug by making i686-* 
imply --with-arch-32=i686 instead of --with-cpu-32=i686, while leaving the 
64-bit defaults (for which mode -march=i686 is invalid) unaffected.

-- 
Joseph S. Myers
joseph@codesourcery.com