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

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Date:	Tue, 3 Oct 2006 13:10:55 -0400
From:	Vivek Goyal <vgoyal@...ibm.com>
To:	linux kernel mailing list <linux-kernel@...r.kernel.org>
Cc:	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: [PATCH 4/12] i386: define __pa_symbol()



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 |    6 ++++++
 1 file changed, 6 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 13:17:58.000000000 -0400
+++ linux-2.6.18-git17-root/include/asm-i386/page.h	2006-10-02 14:36:32.000000000 -0400
@@ -124,6 +124,12 @@ 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)          \
+	({unsigned long v;  \
+	  asm("" : "=r" (v) : "0" (x)); \
+	  __pa(v); })
 #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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