Re: Compilation Unit name

[Josh Stone <jistone at redhat dot com>]

On 03/17/2017 10:18 AM, SASHA NICOLAS DA ROCHA PINHEIRO wrote:
> I did not find the reference about the argument named
> next_cu_header_offset (below I pasted the respective functions
> signatures). Anyway, name orthography apart, what is being used in
> Dyninst with libdwarf is exactly the value of what we called
> next_cu_off, which corresponds to the third parameter of
> dwarf_nextcu(), named in libdw as next_off.

We must have different versions of libdwarf.h, but either way the point
is that this value is not a die offset, just the offset of the next cu.

In your libdwarf code, it looks like you only use "cu_die_off" in the
call to dwarf_next_cu_header_c and for updating the "dies_seen" set.
The latter is suspect, but probably fine in practice.  You don't need
the true die offset because dwarf_siblingof_b uses a NULL die input to
specify that you want the first die of the current cu.  It might help to
call dwarf_dieoffset to see what it actually is.

But libdw doesn't have a notion of a "current" cu, so you do need the
correct offset for dwarf_offdie.  I'm 99% sure cu_off + cu_header_size
is the right value.

> Do you have any other thoughts why the sequence of function calls is
> not working, instead it is giving invalid dwarf?

If the offset I suggest doesn't work, then I'm not sure what's going on.
 Maybe you could share the full code on a branch somewhere, with a test
program to reproduce the problem?