Re: [patch] solib-svr4.c - allow reading linkmap info from core without executable

[Daniel Jacobowitz <drow at false dot org>]

On Fri, Jun 19, 2009 at 04:42:04PM +0200, Mark Kettenis wrote:
> > From: Aleksandar Ristovski <aristovski@qnx.com>
> > Date:  Fri, 19 Jun 2009 10:16:26 -0400
> > 
> > Pedro Alves wrote:
> > > 
> > > I was thinking on pushing the elf check a bit down instead,
> > > like the below.  However, having now tested this, I see that
> > > this doesn't work in most of the cores I have here (x86_64-linux).
> > > In most cases I see, the segment that would contain the program
> > > headers, as indicated by auxv info, isn't included in the
> > > core...
> > > 
> > > (objdump -h)
> > > Idx Name          Size      VMA               LMA               File off  Algn
> > >   :
> > >   6 load1         00000000  0000000000400000  0000000000000000  000008f8  2**0
> > >                   ALLOC, READONLY, CODE
> > >   :
> > > 
> 
> I'm somewhat amazed that the Linux kernel doesn't dump the auxv stuff.
> Without the auxv data, debugging core dumps of PIE executables will be
> impossible.
> 
> Perhaps the kernel does include the information in the does, but bfd
> doesn't have the necessary code to turn it into an .auxv section?

That works fine:

drow@caradoc:~% readelf -n core

Notes at offset 0x00000430 with length 0x00000344:
  Owner         Data size       Description
  CORE          0x00000150      NT_PRSTATUS (prstatus structure)
  CORE          0x00000088      NT_PRPSINFO (prpsinfo structure)
  CORE          0x00000130      NT_AUXV (auxiliary vector)

drow@caradoc:~% objdump -h core

core:     file format elf64-x86-64

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  0 note0         00000344  0000000000000000  0000000000000000  00000430  2**0
                  CONTENTS, READONLY
  1 .reg/14342    000000d8  0000000000000000  0000000000000000  000004b4  2**2
                  CONTENTS
  2 .reg          000000d8  0000000000000000  0000000000000000  000004b4  2**2
                  CONTENTS
  3 .auxv         00000130  0000000000000000  0000000000000000  00000644  2**3
                  CONTENTS

But reading it again, Pedro said "the segment that would contain the
program headers, as indicated by auxv info".  That's probably not
dumped by default, as it's read-only.

-- 
Daniel Jacobowitz
CodeSourcery