Re: BFD relocations -- alpha

[Camm Maguire <camm@enhanced.com>]

Greetings!  OK, I'm starting to work on this a bit, first with the
alpha.  I have a hunch that all I need to do is call _bfd_set_gp_value
on the input bfd with the destination address of the .text section or
some such, and then bfd_get_relocated_section_contents should work.

I would be most grateful if anyone knows ahead of time what this gp
value should be.  It will save me considerable time reading the
sources.

Take care,

Alan Modra <amodra@bigpond.net.au> writes:

> On Sat, Jul 27, 2002 at 12:07:57PM -0400, Camm Maguire wrote:
> > > > 3) Are there recommended guidelines for such patches?  I.e. relatively
> > > > 	safe places for modifications?
> > > 
> > > You'll likely need to implement missing special_function entries for
> > > reloc howto structures.  It may work out easier in some cases to
> > > implement a new get_relocated_section_contents function rather than
> > > trying to use bfd_generic_get_relocated_section_contents.
> > > 
> > 
> > OK.  A standalone get_relocated_section_contents function per arch
> > seems the way to go.  I was contemplating modifying the lower level
> > functions on the order of mips_elf_hi16_reloc, etc., but this does
> > seem more dangerous.  
> 
> If you can do so, use the lower level functions.  The per-arch
> get_relocated_section_contents is really for weird cases.  Hmm, like
> mips.  If you can get mips working properly, any other target will be
> a breeze.
> 
> > The way I'd go about this is to follow what ld does in a debugger.  Is
> > there a better source of information somewhere?
> 
> Some of the ELF processor supplements are available on the web.
> They will help in figuring out how vairous relocations should be
> handled.
> 
> > Also, is there a reason why some arches currently work and others
> > don't?  I.e., is it just oversight thus far due to the fact that no
> > one uses the get_relocated_section_contents, or are there arch
> > specific difficulties which make such a function hard on certain
> > platforms, e.g. the gp_disp, etc.?
> 
> Well, ELF RELA targets generally don't need those special_function
> handlers in order to have a working assembler, and the linker
> relocate_section function is often not any easier to write using
> bfd_perform_relocation.  One of the problems is that the howto
> functions weren't designed for relocs that depend on the value of
> other relocs, or on extraneous data like segment base addresses.
> gp relative relocs are easy enough as the gp base is stashed away
> in the bfd.
> 
> -- 
> Alan Modra
> IBM OzLabs - Linux Technology Centre
> 
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-- 
Camm Maguire			     			camm@enhanced.com
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