[U-Boot] ARM relocation, question to Heiko

[Wolfgang Denk]

Dear Peter Tyser,

In message <1286167382.22760.19.camel at 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

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