[x86 setup] Volatilize asm() statements

asm() statements need to be volatile when:

a. They have side effects (other than value returned).
b. When the value returned can vary over time.
c. When they have ordering constraints that cannot be expressed to gcc.

In particular, the keyboard and timer reads were violating constraint (b),
which resulted in the keyboard/timeout poll getting
loop-invariant-removed when compiling with gcc 4.2.0.

Thanks to an anonymous bug reporter for pointing this out.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/arch/i386/boot/edd.c b/arch/i386/boot/edd.c
index 82b5c846a19..bd138e442ec 100644
--- a/arch/i386/boot/edd.c
+++ b/arch/i386/boot/edd.c
@@ -30,9 +30,9 @@ static int read_mbr(u8 devno, void *buf)
 	cx = 0x0001;		/* Sector 0-0-1 */
 	dx = devno;
 	bx = (size_t)buf;
-	asm("pushfl; stc; int $0x13; setc %%al; popfl"
-	    : "+a" (ax), "+c" (cx), "+d" (dx), "+b" (bx)
-	    : : "esi", "edi", "memory");
+	asm volatile("pushfl; stc; int $0x13; setc %%al; popfl"
+		     : "+a" (ax), "+c" (cx), "+d" (dx), "+b" (bx)
+		     : : "esi", "edi", "memory");
 
 	return -(u8)ax;		/* 0 or -1 */
 }