[U-Boot] ARM relocation, question to Heiko

Wolfgang Denk
2010-10-04T17:06:14Z

Dear "J. William Campbell",

In message <4CA9F294.8080007@comcast.net> you wrote:
>
> Yes, I think Wolfgang is correct. This is not going to be easy to do in
> general. To run anywhere, the code must be true Position Independent
> code. If you intend to use any C code in the initialization, this will
> result in needing -fPIC for at least that code. I am not sure you can
> mix -fPIC and non -fPIC code in the same link, but I expect not. I am a
> bit surprised that it is possible to get even the initialization code to
> be Position Independent, but it appears that on at least some PPC it is
> possible/has been done.

Not really. On PowerPC, only the first 20 or 30 lines of assembler
code in start.S are position independent; then we compute the link
(resp. execution) address and branch to it. From then, we run from the
very address range we were linked for (starting at TEXT_BASE).

> Albert is doing now, and Graeme did before, is the first option,
> creating a loader that understands ELF. This has the advantage that it
> will work on all architectures. However, once this understanding is in
> place, it would be easy to write a small post-processing program that
> would reduce the size of the relocation entries, much like -mrelocatable
> does. This may or may not be necessary, but it is certainly possible.

Eventually we might even add -mrelocatable support for the other
architectures to the tool chain.

Best regards,

Wolfgang Denk

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