Re: [Libunwind-devel] Interest in .debug_frame support?

[Mark Wielaard]

Hi Daniel,

On Wed, 2007-10-03 at 09:24 -0400, Daniel Jacobowitz wrote:
> Corey Ashford asked in February whether there were any plans for
> .debug_frame support.  I have a similar question - is there any
> interest in including .debug_frame support?
> 
> I've been looking at a system where I'd like to have backtraces during
> debugging (from memory allocation debuggers, et cetera).  This is a
> debugging feature, so I'm willing to put extra data on the target
> during it, probably using .gnu_debuglink to point at separate files.
> But the overhead of .eh_frame is not acceptable.

Our use cases seem slightly different since you want to use libunwind
in-process and we would be using it out-of-process (or even use it with
a core file as backend). But in theory we are looking at the same thing
for frysk where we are inspecting a (remote) executable that might not
have an .eh_frame section, but might have a (separate debugfile with
a) .debug_frame section. We already have some support for feeding some
more information from a remote process to libunwind (I am currently
flushing out our patches to the list so they can hopefully be merged,
since the frysk libunwind diverged a bit over the last year). But we
don't yet have the .debug_frame loading, feeding and parsing support
itself.

> The things that would have to be implemented:
> 
>   - Finding and opening files to map .debug_frame.

So in frysk we do this ourselves (using libdwfl from elfutils) and we
would need to feed that to libunwind.

>   - Handling the differences between .debug_frame and .eh_frame.
>   They're important but small.

I was looking for a description of the differences. But it seems people
either just know and if you don't then you have to go through the DWARF
standard and the LSB core specification Exception Frames [1] and
carefully compare them side-by-side. Is there a better description of
the differences?

Cheers,

Mark

[1]
http://refspecs.freestandards.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html