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 (file)
--- a/include/asm-x86/system_32.h
+++ b/include/asm-x86/system_32.h
@@ -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"

diff --git a/include/asm-x86/system_64.h b/include/asm-x86/system_64.h
index 5022aec..fb4bcf9 100644 (file)
--- a/include/asm-x86/system_64.h
+++ b/include/asm-x86/system_64.h
@@ -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;
 }