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Commit c1217a75 authored by Kirill Korotaev's avatar Kirill Korotaev Committed by Thomas Gleixner
Browse files

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):
parent f891dd18

include/asm-x86/system_32.h

+1 −1
Original line number Original line Diff line number Diff line
@@ -142,7 +142,7 @@ static inline unsigned long native_read_cr4_safe(void) 
{

{

	unsigned long val;

	unsigned long val;

	/* This could fault if %cr4 does not exist */

	/* This could fault if %cr4 does not exist */

	asm("1: movl %%cr4, %0		\n"

	asm volatile("1: movl %%cr4, %0		\n"

		"2:				\n"

		"2:				\n"

		".section __ex_table,\"a\"	\n"

		".section __ex_table,\"a\"	\n"

		".long 1b,2b			\n"

		".long 1b,2b			\n"

include/asm-x86/system_64.h

+4 −4
Original line number Original line Diff line number Diff line
@@ -85,7 +85,7 @@ static inline void write_cr0(unsigned long val) 
static inline unsigned long read_cr2(void)

static inline unsigned long read_cr2(void)

{

{

	unsigned long cr2;

	unsigned long cr2;

	asm("movq %%cr2,%0" : "=r" (cr2));

	asm volatile("movq %%cr2,%0" : "=r" (cr2));

	return cr2;

	return cr2;

}

}
@@ -97,7 +97,7 @@ static inline void write_cr2(unsigned long val) 
static inline unsigned long read_cr3(void)

static inline unsigned long read_cr3(void)

{ 

{ 

	unsigned long cr3;

	unsigned long cr3;

	asm("movq %%cr3,%0" : "=r" (cr3));

	asm volatile("movq %%cr3,%0" : "=r" (cr3));

	return cr3;

	return cr3;

}

}
@@ -109,7 +109,7 @@ static inline void write_cr3(unsigned long val) 
static inline unsigned long read_cr4(void)

static inline unsigned long read_cr4(void)

{ 

{ 

	unsigned long cr4;

	unsigned long cr4;

	asm("movq %%cr4,%0" : "=r" (cr4));

	asm volatile("movq %%cr4,%0" : "=r" (cr4));

	return cr4;

	return cr4;

}

}
@@ -121,7 +121,7 @@ static inline void write_cr4(unsigned long val) 
static inline unsigned long read_cr8(void)

static inline unsigned long read_cr8(void)

{

{

	unsigned long cr8;

	unsigned long cr8;

	asm("movq %%cr8,%0" : "=r" (cr8));

	asm volatile("movq %%cr8,%0" : "=r" (cr8));

	return cr8;

	return cr8;

}

}