Re: [RFA] dwarf2-frame.c sign extension patch

Daniel Jacobowitz
2004-07-22T00:47:19Z

On Wed, Jul 21, 2004 at 05:41:36PM -0700, Kevin Buettner wrote:
> On Wed, 21 Jul 2004 17:17:23 -0400
> Daniel Jacobowitz <drow@false.org> wrote:
>
> > The rest I have no comment on, but this issue I know...
> >
> > On Wed, Jul 21, 2004 at 10:29:43PM +0200, Mark Kettenis wrote:
> > > (dwarf2_build_frame_info): Set unit.addr_size.
> > >
> > > Why is the old code wrong? The comment clearly says "from unit
> > > header" which is what the DWARF standard says (or at least implies).
> > > Theoretically it could change from compilation unit to compilation
> > > unit. So I think your change to replace it by
> > > TYPE_LENGTH(builtin_type_void_data_ptr) is wrong.
> >
> > The old code doesn't do it from the compilation unit header either:
> > - unit.addr_size = objfile->obfd->arch_info->bits_per_address / 8;
> > + unit.addr_size = TYPE_LENGTH (builtin_type_void_data_ptr);
> >
> > Any use of bits_per_address, IMO, is a bug. Take a look at how this
> > field is set on MIPS; it's based on the architecture, not the ABI or
> > the pointer size or the dwarf address size or anything like that.
>
> I agree.
>
> > TYPE_LENGTH doesn't seem like an ideal replacement. Can we use the
> > value in the compilation unit header here?
>
> I considered doing this, but was told that the information in
> .debug_frame should be independent of the CU header. I really
> don't know what the "right" solution is.

Oh, right, we're in .debug_frame here. I care very much about being
.able to use .debug_frame without .debug_info. Debian distributes
library images with only .debug_frame, to provide backtraces.

.debug_frame doesn't provide this information. That's a known defect;
I think that Jim proposed correcting it on the dwarf2 list.

Does anyone know if .eh_frame solves this problem somehow?

Otherwise, I think that using TYPE_LENGTH (with a big comment
explaining the issue) may be the best we can do.

--
Daniel Jacobowitz