Re: Fedora 14 debug proposal

[Tom Tromey <tromey@redhat.com>]

>>>>> "Roland" == Roland McGrath <roland@redhat.com> writes:

Roland> For Fedora purposes, dropping .debug_pub* sections could just as
Roland> well be done in the stripping stage.  And, I don't think they
Roland> really cost much space in the grand scheme of things.  So there
Roland> is little real motivation to fiddle gcc at all until after we
Roland> have completed basically everything else in the related realms.

Doing it in gcc can save some space, by not putting useless stuff into
the string table.  I didn't try to measure this.  Just stripping the
sections does not save much space, as you hypothesized; I did a test
with objcopy on all the debuginfo I have currently installed (OO.o plus
other random bits):

opsy. du -s debug stripped
1883432	debug
1812156	stripped
  71276 savings

The indices are about 3x the size of the savings:

opsy. du -s Out
208876	Out

Tom> 3. If we are shipping GCC 4.5 in F14, I think we should enable the
Tom> .debug_types stuff by default.  This will shrink debuginfo and it
Tom> makes gdb use less memory.

Roland> libdw does not yet handle .debug_types.  It of course will, but
Roland> I wouldn't like to have a gcc defaults change on any queue until
Roland> we are quite concrete with getting all the support in line.

Yeah, that would be good for us too; some of the recent gcc changes
caught us by surprise.  OTOH I don't want to stop Jakub's gusto, maybe
just get a little more warning of coming gdb-impacting changes.

Tom> This one is optional, in particular I assume it will be subsumed by
Tom> the other DWARF compression work.

Roland> It should be, yes.  I don't see any reason that .debug_types and
Roland> DW_FORM_ref_sig8 need to survive final linking.  The normal reference
Roland> forms are more efficient for consumers to use.

Why is that?  I looked at the gdb code here and nothing really stood out.

Tom