linux-kernel - Re: [PATCH 4/12] i386: define __pa

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Date:	Fri, 6 Oct 2006 14:33:25 -0400
From:	Vivek Goyal <vgoyal@...ibm.com>
To:	Franck Bui-Huu <vagabon.xyz@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Reloc Kernel List <fastboot@...ts.osdl.org>,
	ebiederm@...ssion.com, akpm@...l.org, ak@...e.de,
	horms@...ge.net.au, lace@...kratochvil.net, hpa@...or.com,
	magnus.damm@...il.com, lwang@...hat.com, dzickus@...hat.com,
	maneesh@...ibm.com
Subject: Re: [PATCH 4/12] i386: define __pa_symbol()

On Fri, Oct 06, 2006 at 03:10:58PM +0200, Franck Bui-Huu wrote:
> Vivek Goyal wrote:
> 
> > +/* __pa_symbol should be used for C visible symbols.
> > +   This seems to be the official gcc blessed way to do such arithmetic. */
> > +#define __pa_symbol(x)          __pa(RELOC_HIDE((unsigned long)x,0))
> 
> #define __pa_symbol(x)          __pa(RELOC_HIDE((unsigned long)(x),0))
>                                                                ^^^
> ... should be better. You should not rely on RELOC_HIDE implementation.
>

Thanks Franck. Done.



On x86_64 we have to be careful with calculating the physical
address of kernel symbols.  Both because of compiler odditities
and because the symbols live in a different range of the virtual
address space.

Having a defintition of __pa_symbol that works on both x86_64 and
i386 simplifies writing code that works for both x86_64 and
i386 that has these kinds of dependencies.

So this patch adds the trivial i386 __pa_symbol definition.

Added assembly magic similar to RELOC_HIDE as suggested by Andi Kleen.
Just picked it up from x86_64.

Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Vivek Goyal <vgoyal@...ibm.com>
---

 include/asm-i386/page.h |    3 +++
 1 file changed, 3 insertions(+)

diff -puN include/asm-i386/page.h~i386-define-__pa_symbol include/asm-i386/page.h
--- linux-2.6.18-git17/include/asm-i386/page.h~i386-define-__pa_symbol	2006-10-02 14:39:18.000000000 -0400
+++ linux-2.6.18-git17-root/include/asm-i386/page.h	2006-10-06 13:09:25.000000000 -0400
@@ -124,6 +124,9 @@ extern int page_is_ram(unsigned long pag
 #define VMALLOC_RESERVE		((unsigned long)__VMALLOC_RESERVE)
 #define MAXMEM			(-__PAGE_OFFSET-__VMALLOC_RESERVE)
 #define __pa(x)			((unsigned long)(x)-PAGE_OFFSET)
+/* __pa_symbol should be used for C visible symbols.
+   This seems to be the official gcc blessed way to do such arithmetic. */
+#define __pa_symbol(x)          __pa(RELOC_HIDE((unsigned long)(x),0))
 #define __va(x)			((void *)((unsigned long)(x)+PAGE_OFFSET))
 #define pfn_to_kaddr(pfn)      __va((pfn) << PAGE_SHIFT)
 #ifdef CONFIG_FLATMEM
_

 
-
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