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Re: [Gcl-devel] Re: BFD relocations

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

> 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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