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

[Haavard Skinnemoen]

On Fri, 25 Jul 2008 11:21:12 -0400
Jerry Van Baren <gerald.vanbaren at ge.com> wrote:

> The relocation information is in the ELF file until and unless we remove 
> it.  "Normal" ELF executables retain that relocation information... that 
> is exactly what the "L" (it) is for.  The linux loader (elf loader) 
> loads an executable into an arbitrary memory location and relocates it 
> by fixing up addresses based on the relocation table.

You're mixing two different relocation tables. Statically linked
executables (like u-boot) normally don't have any relocation
information in them after they are fully linked. Dynamically linked
executables, position-independent executables (PIE) and shared
libraries have dynamic relocations which are not only in the ELF file,
but in a loadable segment so that they can be accessed at run time.

The relocation information from the .o files are not preserved in the
final executable unless you specify the --emit-relocs flags, which
exists purely for debugging purposes. The relocations used by the
dynamic loader come from an entirely different, simpler set of
relocation types which are normally not found in .o files.

Why do you think objdump has two different options for dumping normal
(-r) vs. dynamic (-R) relocations?

And no, Linux ELF executables can _not_ be loaded into an arbitrary
memory location unless they are PIE. Shared libraries, however, can be
loaded at arbitrary memory locations, though things like pre-linking
might make it more optimal to try to place them at the same address
everywhere.

Ok, I'll stop the chest-beating now. But please stop trying to tell
people that adding a powerpc-specific option (which nobody seems to
know how really works) to the command line will work on any other
architectures than powerpc.

Haavard