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Date: Fri, 25 Aug 2006 09:31:52 +1000 From: Paul Mackerras <paulus@...ba.org> To: Christoph Lameter <clameter@....com> Cc: Dong Feng <middle.fengdong@...il.com>, linux-kernel@...r.kernel.org, ak@...e.de Subject: Re: Unnecessary Relocation Hiding? 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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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