[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, 6 insertions, 6 deletions

diff --git a/arch/i386/boot/video-vga.c b/arch/i386/boot/video-vga.c
index 700d09a9c9b3..d660e608cd58 100644
--- a/arch/i386/boot/video-vga.c
+++ b/arch/i386/boot/video-vga.c
@@ -47,16 +47,16 @@ static u8 vga_set_basic_mode(void)
 
 #ifdef CONFIG_VIDEO_400_HACK
         if (adapter >= ADAPTER_VGA) {
-                asm(INT10
-                    : : "a" (0x1202), "b" (0x0030)
-                    : "ecx", "edx", "esi", "edi");
+                asm volatile(INT10
+                             : : "a" (0x1202), "b" (0x0030)
+                             : "ecx", "edx", "esi", "edi");
         }
 #endif
 
         ax = 0x0f00;
-        asm(INT10
-            : "+a" (ax)
-            : : "ebx", "ecx", "edx", "esi", "edi");
+        asm volatile(INT10
+                     : "+a" (ax)
+                     : : "ebx", "ecx", "edx", "esi", "edi");
 
         mode = (u8)ax;