x86: mark read_crX() asm code as volatile

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>

diff --git a/include/asm-i386/system.h b/include/asm-i386/system.h
index d69ba937e09251769e2f00d54c0c91562a4127e8..b10465542948cd1fc3a14568719779854394445f 100644 (file)
--- a/include/asm-i386/system.h
+++ b/include/asm-i386/system.h
@@ -141,7 +141,7 @@ 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_64/system.h b/include/asm-x86_64/system.h
index 02175aa1d16a8aea903a51e6b5e1c71fda57d075..47682a6520f6f5eec483ceb68779dc9d8ebf8f72 100644 (file)
--- a/include/asm-x86_64/system.h
+++ b/include/asm-x86_64/system.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;
 }