Re: unwind support for Linux 2.6 vsyscall DSO

[Roland McGrath <roland at redhat dot com>]

> > Should this SOLIB_ADD then just store whether it has checked yet and clear
> > that record in SOLIB_CLEAR?
> 
> I think that's what it would take.  Open to better ideas, I'm just
> doing the best I can. :)

Ok.  I don't see a problem with this if the sequence of when SOLIB_ADD and
SOLIB_CLEAR will be called is correct.  That is, SOLIB_ADD after core load,
after attach, or after the break-on-exec (second one) from run, and
SOLIB_CLEAR some appropriate time for unloading symbols.  It's important
that SOLIB_ADD not be called too early in the run case, i.e. before the
second exec so that the inferior's state is not yet as it will be.
Can I rely on that not happening?

> When I say "target vector", I mean 'struct target_ops', not 'struct
> gdbarch'.  

I understood you.  My only point was that the notion of such a hook is
ELF-specific and so perhaps that says something about whether an addition
of a hook to the generic target_ops structure is appropriate.

> Yeah, I had in mind another elf-specific BFD function, like the one
> that reads the solib data from memory.  All I'm suggesting is, take
> the code that you've got, move it into bfd, and call it
> bfd_elf_auxilliary_vector_sysinfo_ehdr.

Ok.  A function quite that specific seems really pointless to me.  Some
sort of `bfd_elf_decode_auxv' that either gives an AT_* value to search
for, or translates one or all entries into Elf_Internal_Auxv format seems
more appropriate.  e.g.:

bfd_error bfd_elf_decode_auxv (bfd *, char **data, bfd_size_type *nbytes,
			       Elf_Internal_Auxv *element);

used as in:

	{
	  Elf_Internal_Auxv av;
	  char *p = contents;
	  bfd_size_type n = contents_size;
	  while (bfd_elf_decode_auxv (abfd, &p, &n, &av) == bfd_error_no_error)
	    if (av.a_type == AT_SYSINFO_EHDR)
	      {
		do_stuff (av.a_val);
		break;
	      }
	}

or:

bfd_error bfd_elf_auxv_extract (bfd *, char *data, bfd_size_type nbytes,
			        bfd_vma tag, bfd_vma *val);

used as in:

	{
	  bfd_vma val;
	  if (bfd_elf_auxv_extract (abfd, contents, contents_size,
				    AT_SYSINFO_EHDR, &val) == bfd_error_no_error)
	    do_stuff (av.a_val);
	}


Thanks,
Roland