Re: libstdc++ atomicity.h and ppc405 problem

[dank at kegel dot com]

Phil Edwards wrote:
> While experimenting, however, you might configure your build with the
>     --enable-cxx-flags='-mcpu=405'
> option.  That's a hook described in the libstdc++ documentation as a way of
> passing arbitrary options to the libstdc++ build.  (But only that library,
> and the flags are not turned on automatically for users of the installed
> compiler/libs.  They are build-time only.)

Thanks very much for the tip.

> Most people don't learn about multilibs until they break them; count
> yourself ahead of the curve.
> 
> You are about to learn (if you don't know already) of another aspect of
> GCC development, however:  port maintainership.  The gcc/config/.... files
> are outside the realm of libstdc++.  So while a multilibs change like the
> one above may be an appropriate solution, you would have to convince
> 
>     fenric 4% grep rs6000 MAINTAINERS
>     rs6000 port             Geoff Keating           geoffk@redhat.com
>     rs6000 port             David Edelsohn          dje@watson.ibm.com
>     fenric 5%
> 
> on the gcc-patches mailing list to make the change.

That's good to know, thanks.

> Since adding options to
> the multilibs list exponentially increases the time it takes to bootstrap
> gcc, most such changes are frowned upon.  So in the worst case (from your
> point of view), you might have to maintain the change as a third party patch.

I imagine I could add an --enable-ppc405 switch to
config-ml.in to enable the new library; that would make it
so people who didn't need this workaround wouldn't have to
deal with the longer build time.  Um, that is, if I can figure
out config-ml.in, which is quite confusing.

- Dan