linux-kernel - Re: Unnecessary Relocation Hiding?

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Message-ID: <a2ebde260608241830p2d26b20bp6bfb9b1b5a267ec6@mail.gmail.com>
Date:	Fri, 25 Aug 2006 09:30:21 +0800
From:	"Dong Feng" <middle.fengdong@...il.com>
To:	"Paul Mackerras" <paulus@...ba.org>, ak@...e.de
Cc:	"Christoph Lameter" <clameter@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: Unnecessary Relocation Hiding?

Sorry for perhaps extending the specific question to a more generic
one. In which cases shall we, in current or future development,
prevent gcc from knowing a pointer-addition in the way RELOC_HIDE? And
in what cases shall we just write pure C point addition?

After all, we are writing an OS in C not in pure assembly, so I am
just trying to learn some generial rules to mimize the raw assembly in
development.

Feng,Dong


2006/8/25, Paul Mackerras <paulus@...ba.org>:
> Christoph Lameter writes:
>
> 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.
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