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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):
hifive-unleashed-5.1
Kirill Korotaev 2007-10-17 18:04:33 +02:00 committed by Thomas Gleixner
parent f891dd18c1
commit c1217a75ea
2 changed files with 5 additions and 5 deletions
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2
include/asm-x86/system_32.h
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@ -142,7 +142,7 @@ static inline unsigned long native_read_cr4_safe(void)
{
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"

8
include/asm-x86/system_64.h
View File

@ -85,7 +85,7 @@ static inline void write_cr0(unsigned long val)
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 long val)
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 long val)
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 long val)
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;
}