Re: Unnecessary Relocation Hiding?

[Paul Mackerras <paulus@samba.org>]

Christoph Lameter writes:

> On Wed, 23 Aug 2006, Dong Feng wrote:
> 
> > I have a question. Why shall we need a RELOC_HIDE() macro in the
> > definition of per_cpu()? Maybe the question is actually why we need
> > macro RELOC_HIDE() at all. I changed the following line in
> > include/asm-generic/percpu.h, from
> 
> Guess it was copied from IA64 but the semantics were not preserved.
> I think it should either be changed the way you suggest or the 
> implementation needs to be fixed to actually do a linker relocation.

No, RELOC_HIDE came from ppc originally.  The reason for it is that
gcc assumes that if you add something on to the address of a symbol,
the resulting address is still inside the bounds of the symbol, and do
optimizations based on that.  The RELOC_HIDE macro is designed to
prevent gcc knowing that the resulting pointer is obtained by adding
an offset to the address of a symbol.  As far as gcc knows, the
resulting pointer could point to anything.

It has nothing to do with linker relocations.

Paul.