[patch 20/29] x86: mark read_crX() asm code as volatile

Greg Kroah-Hartman
2007-11-20T18:34:40Z

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[-- Type: text/plain, Size: 2143 bytes --]

2.6.23-stable review patch. If anyone has any objections, please let us
know.

------------------
From: Kirill Korotaev <dev@openvz.org>

patch c1217a75ea102d4e69321f210fab60bc47b9a48e in mainline.

x86: mark read_crX() asm code as volatile

Some gcc versions (I checked at least 4.1.1 from RHEL5 & 4.1.2 from gentoo)
can generate incorrect code with read_crX()/write_crX() functions mix up,
due to cached results of read_crX().

The small app for x8664 below compiled with -O2 demonstrates this
(i686 does the same thing):

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
include/asm-i386/system.h | 2 +-
include/asm-x86_64/system.h | 8 ++++----
2 files changed, 5 insertions(+), 5 deletions(-)

--- a/include/asm-i386/system.h
+++ b/include/asm-i386/system.h
@@ -141,7 +141,7 @@ static inline unsigned long native_read_
{
unsigned long val;
/* This could fault if %cr4 does not exist */
- asm("1: movl %%cr4, %0 \n"
+ asm volatile("1: movl %%cr4, %0 \n"
"2: \n"
".section __ex_table,\"a\" \n"
".long 1b,2b \n"
--- a/include/asm-x86_64/system.h
+++ b/include/asm-x86_64/system.h
@@ -85,7 +85,7 @@ static inline void write_cr0(unsigned lo
static inline unsigned long read_cr2(void)
{
unsigned long cr2;
- asm("movq %%cr2,%0" : "=r" (cr2));
+ asm volatile("movq %%cr2,%0" : "=r" (cr2));
return cr2;
}

@@ -97,7 +97,7 @@ static inline void write_cr2(unsigned lo
static inline unsigned long read_cr3(void)
{
unsigned long cr3;
- asm("movq %%cr3,%0" : "=r" (cr3));
+ asm volatile("movq %%cr3,%0" : "=r" (cr3));
return cr3;
}

@@ -109,7 +109,7 @@ static inline void write_cr3(unsigned lo
static inline unsigned long read_cr4(void)
{
unsigned long cr4;
- asm("movq %%cr4,%0" : "=r" (cr4));
+ asm volatile("movq %%cr4,%0" : "=r" (cr4));
return cr4;
}

@@ -121,7 +121,7 @@ static inline void write_cr4(unsigned lo
static inline unsigned long read_cr8(void)
{
unsigned long cr8;
- asm("movq %%cr8,%0" : "=r" (cr8));
+ asm volatile("movq %%cr8,%0" : "=r" (cr8));
return cr8;
}

--