[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>

arch/i386/boot/boot.h

@@ -87,7 +87,7 @@ static inline void set_fs(u16 seg)
 static inline u16 fs(void)
 {
 	u16 seg;
-	asm("movw %%fs,%0" : "=rm" (seg));
+	asm volatile("movw %%fs,%0" : "=rm" (seg));
 	return seg;
 }
 
@@ -98,7 +98,7 @@ static inline void set_gs(u16 seg)
 static inline u16 gs(void)
 {
 	u16 seg;
-	asm("movw %%gs,%0" : "=rm" (seg));
+	asm volatile("movw %%gs,%0" : "=rm" (seg));
 	return seg;
 }
 
@@ -107,19 +107,19 @@ typedef unsigned int addr_t;
 static inline u8 rdfs8(addr_t addr)
 {
 	u8 v;
-	asm("movb %%fs:%1,%0" : "=r" (v) : "m" (*(u8 *)addr));
+	asm volatile("movb %%fs:%1,%0" : "=r" (v) : "m" (*(u8 *)addr));
 	return v;
 }
 static inline u16 rdfs16(addr_t addr)
 {
 	u16 v;
-	asm("movw %%fs:%1,%0" : "=r" (v) : "m" (*(u16 *)addr));
+	asm volatile("movw %%fs:%1,%0" : "=r" (v) : "m" (*(u16 *)addr));
 	return v;
 }
 static inline u32 rdfs32(addr_t addr)
 {
 	u32 v;
-	asm("movl %%fs:%1,%0" : "=r" (v) : "m" (*(u32 *)addr));
+	asm volatile("movl %%fs:%1,%0" : "=r" (v) : "m" (*(u32 *)addr));
 	return v;
 }
 
@@ -139,19 +139,19 @@ static inline void wrfs32(u32 v, addr_t addr)
 static inline u8 rdgs8(addr_t addr)
 {
 	u8 v;
-	asm("movb %%gs:%1,%0" : "=r" (v) : "m" (*(u8 *)addr));
+	asm volatile("movb %%gs:%1,%0" : "=r" (v) : "m" (*(u8 *)addr));
 	return v;
 }
 static inline u16 rdgs16(addr_t addr)
 {
 	u16 v;
-	asm("movw %%gs:%1,%0" : "=r" (v) : "m" (*(u16 *)addr));
+	asm volatile("movw %%gs:%1,%0" : "=r" (v) : "m" (*(u16 *)addr));
 	return v;
 }
 static inline u32 rdgs32(addr_t addr)
 {
 	u32 v;
-	asm("movl %%gs:%1,%0" : "=r" (v) : "m" (*(u32 *)addr));
+	asm volatile("movl %%gs:%1,%0" : "=r" (v) : "m" (*(u32 *)addr));
 	return v;
 }
 
@@ -180,15 +180,15 @@ static inline int memcmp(const void *s1, const void *s2, size_t len)
 static inline int memcmp_fs(const void *s1, addr_t s2, size_t len)
 {
 	u8 diff;
-	asm("fs; repe; cmpsb; setnz %0"
-	    : "=qm" (diff), "+D" (s1), "+S" (s2), "+c" (len));
+	asm volatile("fs; repe; cmpsb; setnz %0"
+		     : "=qm" (diff), "+D" (s1), "+S" (s2), "+c" (len));
 	return diff;
 }
 static inline int memcmp_gs(const void *s1, addr_t s2, size_t len)
 {
 	u8 diff;
-	asm("gs; repe; cmpsb; setnz %0"
-	    : "=qm" (diff), "+D" (s1), "+S" (s2), "+c" (len));
+	asm volatile("gs; repe; cmpsb; setnz %0"
+		     : "=qm" (diff), "+D" (s1), "+S" (s2), "+c" (len));
 	return diff;
 }
 

arch/i386/boot/cpucheck.c

@@ -96,7 +96,8 @@ static int has_fpu(void)
 		asm volatile("movl %0,%%cr0" : : "r" (cr0));
 	}
 
-	asm("fninit ; fnstsw %0 ; fnstcw %1" : "+m" (fsw), "+m" (fcw));
+	asm volatile("fninit ; fnstsw %0 ; fnstcw %1"
+		     : "+m" (fsw), "+m" (fcw));
 
 	return fsw == 0 && (fcw & 0x103f) == 0x003f;
 }

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 */
 }

arch/i386/boot/tty.c

@@ -54,9 +54,9 @@ static u8 gettime(void)
 	u16 ax = 0x0200;
 	u16 cx, dx;
 
-	asm("int $0x1a"
-	    : "+a" (ax), "=c" (cx), "=d" (dx)
-	    : : "ebx", "esi", "edi");
+	asm volatile("int $0x1a"
+		     : "+a" (ax), "=c" (cx), "=d" (dx)
+		     : : "ebx", "esi", "edi");
 
 	return dx >> 8;
 }
@@ -67,17 +67,17 @@ static u8 gettime(void)
 int getchar(void)
 {
 	u16 ax = 0;
-	asm("int $0x16" : "+a" (ax));
+	asm volatile("int $0x16" : "+a" (ax));
 
 	return ax & 0xff;
 }
 
 static int kbd_pending(void)
 {
 	u8 pending;
-	asm("int $0x16; setnz %0"
-	    : "=rm" (pending)
-	    : "a" (0x0100));
+	asm volatile("int $0x16; setnz %0"
+		     : "=rm" (pending)
+		     : "a" (0x0100));
 	return pending;
 }
 

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;