Re: using BFD to load and reloc a simple file

[thockin at hockin dot org]

On Thu, Mar 02, 2006 at 04:18:00PM -0500, Daniel Jacobowitz wrote:
> On Thu, Mar 02, 2006 at 01:15:18PM -0800, thockin@hockin.org wrote:
> > I am trying to load and relocate a simple ELF executable.  It's entirely
> > self contained, but needs to be loadable at an arbitrary 32 bit address.
> > 
> > I'm trying to use libbfd for this, but I am having trouble.  The load goes
> > fine, and it copies the ELF data into memory where I tell it to.  Very
> > nice and very easy.  When I call perform_relocation(), though, it goes
> > haywire.
> 
> That's because this is a routine for the linker, not a routine for
> in-place relocation.

Is there an in-place variant?

> > bfd_perform_relocation() eventually does:
> > 	reloc_target_output_section = symbol->section->output_section;
> > 
> > The problem is that output_section is always NULL.  I don't want to output
> > a BFD, I want to relocate it in memory.
> 
> You might be able to set the section to point at itself.  However, I'm
> not sure if bfd_perform_relocation even does the operation you want it
> to.

I tried that and it stopped finding any relocations at all!  I did not
debug further.

I'm not sure that I am doing what I want to do most effectively.  The end
goal is a small self-contained executable with a few sections that will be
located into memory at some system-specific addresses (which can not be
known at build time).

I've succeeded in making a static binary that works for a given fixed
address.  Now I need to make it relocateable.  Linking with -r seems to
give me the binary I want (though I am not sure it would catch
unresolvable references anymore).

Would I be better off using -pie or some other method?

> -- 
> Daniel Jacobowitz
> CodeSourcery

-- 
Tim Hockin
thockin@hockin.org
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