debug problem with prelinked libraries

[Andrew Stubbs]

Hi all,

I'm trying to get to the bottom of a problem debugging prelinked 
libraries. I've fixed a few aspects of the problem, but the further I 
get into it the more I think I must be missing something. I mean, 
debugging prelinked libraries is supposed to Just Work, right? But I 
can't see how it could ever have worked.

First, I should say that I'm trying to debug a core dump that includes 
prelinked libraries. Is that different somehow? The target is mips, if 
that makes any difference. Also, debugging works fine for the 
non-prelinked libraries and core file, so the problem's not there.

I originally encountered the problem with (a somewhat patched) 
6.6.50_20070925, but I'm seeing exactly the same trouble in the latest 
from CVS.

The problem is that GDB does not find the symbols and debug info for the 
code in the prelinked libraries.

Upon closer inspection, I find that the psymtab has the textlow and 
texthigh addresses as the original file-offsets, before relocation. This 
appears to be because it calculates the section offset as the difference 
between the actual address and the ELF VMA, but the file is prelinked, 
so the offset is zero, and the debug info and symbols are then not 
relocated.

So, I inserted a little code to fixup the offset in the psymtab for the 
prelinked cases, but it now loads the symtab with exactly the same 
offset troubles. So, I try to fix those, and the problem just moves one 
step further on. Surely I can't need to implement prelink support from 
scratch, so I must be missing something?

Is there one place that this should be fixed? I think I need to adjust 
the base address used by the debug info, but I don't know how to do it 
without also changing the base address used for relocating the binaries.

Any other suggestions? Any help would be much appreciated.

Andrew