Re: bfd_get_relocated_section_contents on hppa and ia64

[Nick Clifton <nickc at redhat dot com>]

Hi Camm,

> Greetings!  I can't seem to find documentation anywhere on the sparc64
> R_SPARC_OLO10 reloc, sometimes reported as a R_SPARC_LO10 and a
> R_SPARC_13.

I think that R_SPARC_0LO10 and R_SPARC_LO10 are subtly different...

> I know there is a special addend encoded in the reloc
> type.  Can you explain to me or point out to me how this reloc is
> supposed to work?

I am not a Sparc expert, but I will give it a go.  I could not find any 
actual documentation on Sparc relocs, so I have resorted to looking in 
the sources.  In gas/doc/c-sparc.texi it says:

  "When assembling for 64-bit, and a secondary constant
   addend is specified in an address expression that would
   normally generate an R_SPARC_LO10 relocation, the
   assembler will emit an R_SPARC_OLO10 instead."

So I think that R_SPARC_OLO10 is a slight variation on the R_SPARC_LO10 
reloc.  Looking in bfd/elfxx-sparc.c:_bfd_sparc_elf_relocate_section() I 
see that the reloc is implemented as:

   x = (x & ~(bfd_vma) 0x1fff) | (relocation & 0x1fff);

Ie it clears the bottom 13 bits of the instruction and then inserts the 
value of the relocation into those bits.  (I assume that this relocation 
is being applied to a Sparc bitwise logical instruction which has a 
signed immediate value in its bottom 13 bits).

This seems to be very similar to the R_SPARC_LO10 relocation, except 
that that one appears to affect only the bottom 10 bits of the instruction.

There is one other interesting point.  In the _bfd_sparc_elf_howto_table 
in elfxx-sparc.c the implementation of the R_SPARC_OLO10 reloc is 
assigned to the sparc_elf_notsup_reloc() function.  Thus it may be that 
it is a deprecated reloc that should no longer be used.

Cheers
  Nick