[U-Boot-Users] Changing u-boot relocation scheme

[Haavard Skinnemoen <haavard.skinnemoen@atmel.com>]

On Fri, 25 Jul 2008 22:51:09 +0200
kenneth johansson <kenneth@southpole.se> wrote:

> > Hmm...looks like linking with -pie (or --pic-executable) does
> > something vaguely resembling the trick. But I don't know what vintage
> > of ld you need for this to be available and actually work...  
> 
> Can't see any reason for using this flag over -fPIC for a program like
> u-boot.

You need both. One is a compiler flag, the other is a linker flag. The
linker will probably barf if you try to create a PIC executable from
modules that were not compiled with -fPIC.

On the other hand, using -fPIC but not -pie takes us about 95% of the
way to a fully relocatable u-boot, and is what PowerPC, AVR32 and
others are doing today. The remaining cases -- static and global
initialized pointers -- are fixed up manually.

If we link with -pie and add a bit of code to handle the dynamic
relocations, we could get rid of the manual fixups. I don't know if the
result would be larger or smaller than what we have today, but it would
probably be a bit more robust.

> > Does this really work without any relocation? Or is it being relocated
> > and I'm just too blind to see it?  
> 
> No you are right there is probably many places like this. the code just
> use the old location and that works most of the time.

Ah, of course. The strings are probably read directly from flash.

Haavard