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):
diff --git a/include/asm-x86/system_32.h b/include/asm-x86/system_32.h
index d84e593..1d6fb3a 100644
--- a/include/asm-x86/system_32.h
+++ b/include/asm-x86/system_32.h
@@ -142,7 +142,7 @@
{
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"
diff --git a/include/asm-x86/system_64.h b/include/asm-x86/system_64.h
index 5022aec..fb4bcf9 100644
--- a/include/asm-x86/system_64.h
+++ b/include/asm-x86/system_64.h
@@ -85,7 +85,7 @@
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 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 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 unsigned long read_cr8(void)
{
unsigned long cr8;
- asm("movq %%cr8,%0" : "=r" (cr8));
+ asm volatile("movq %%cr8,%0" : "=r" (cr8));
return cr8;
}