Dear Peter Tyser,
In message 1286167382.22760.19.camel@ptyser-laptop you wrote:
Peter, could you please fill in the details of that old story?
I haven't been following the ARM relocation thread very closely, but a summary of the PPC relocation is:
- Prior to commit 858290178f222d998b6425d85cf06822467918f3 PPC supported
basic relocation, but didn't relocate static pointers, eg pointers in a structure, such as the strings in the cmd_pca953x[] table. So we had to use the hokey "struct->field += gd->reloc_off" fixups that we still have for some arches.
- Adding "-mrelocatable" to the gcc's flags would add additional
relocation info into the ".fixup" section that allowed us to properly fixup static pointers and get rid of the "+= gd->reloc_off" fixups. The additional fixup code was relatively small, in the 1-2% ballpark I think.
- Unfortunately "-mrelocatable" is PPC specific. I remember dabbling
with other, more general relocation flags like -fPIC, pie, etc, but went with -mrelocatable mainly because it was a smaller, easier change. We could share the already-used relocation fixup code in many PPC arch's start.S, so it wasn't too hard to get working unlike the other relocation schemes.
- Graeme Russ was working on relocation for x86 near the same time. He
started this thread which may provide useful info: http://www.mail-archive.com/u-boot@lists.denx.de/msg23347.html He discusses the impact of other compile flags, most of which were generic so could apply to this ARM discussion hopefully.
Thanks alot for the summary.
Best regards,
Wolfgang Denk