Re: MIPS: should -funwind-tables option be made default one on MIPS

[David Daney <ddaney dot cavm at gmail dot com>]

On 03/13/2012 02:10 PM, Ian Lance Taylor wrote:
> Manjunath Matti<manjunath81@gmail.com>  writes:
>
> > In glibc the following commit adds support for backtrace in MIPS port.
> > commit  04d450263622ae7c37cb841f93b3bcf4e9397a88
> >
> > Link: http://repo.or.cz/w/glibc-ports.git/commit/04d450263622ae7c37cb841f93b3bcf4e9397a88
> >
> > But during compilations of any program the user needs to provide/pass
> > -funwind-tables to GCC, to be able to do a backtrace.
> > I am proposing why not the option be made the default one! it would be
> > useful to all.
> > Please let me know if its ok, I have a patch which will enable
> > -funwind-tables as a default option.
>
> The -funwind-tables option takes up space in the program.  That is
> undesirable for programs running on embedded systems that do not need to
> call backtrace or throw exceptions.  Given this, each programmer has to
> decide whether to use the option, and GCC has to pick a sensible
> default.  The default GCC has chosen is to turn off -funwind-tables
> unless the language requires it (e.g., C++, Java, Go) or the processor
> ABI requires it (x86_64).
>
> You are proposing to change the default for MIPS.  That would not be the
> normal default for GCC.  However, it's fine by me if the MIPS
> maintainers want to make that change.  Those are the people you have to
> convince.  Search for "mips" in the top-level MAINTAINERS file in the
> gcc source code.

I am not a maintainer, but I suspect that we don't want to do this just yet.

A lot of mips code is run on resource constrained systems, where this 
will not be welcome.

mips64 on the other hand might be a different question, although there 
is a lot of legacy code out there that doesn't do it, so you might still 
end up with a broken backtrace().

But really how hard is it to manually supply -funwind-tables for objects 
that you care about?

David Daney