Commit b015124e authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

[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: default avatarH. Peter Anvin <hpa@zytor.com>
parent b377fd39

arch/i386/boot/boot.h

+12 −12
Original line number Diff line number Diff line
@@ -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;

}
@@ -180,14 +180,14 @@ 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"

	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"

	asm volatile("gs; repe; cmpsb; setnz %0"

		     : "=qm" (diff), "+D" (s1), "+S" (s2), "+c" (len));

	return diff;

}

arch/i386/boot/cpucheck.c

+2 −1
Original line number Diff line number Diff line
@@ -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

+3 −3
Original line number Diff line number Diff line
@@ -30,7 +30,7 @@ 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"

	asm volatile("pushfl; stc; int $0x13; setc %%al; popfl"

		     : "+a" (ax), "+c" (cx), "+d" (dx), "+b" (bx)

		     : : "esi", "edi", "memory");

arch/i386/boot/tty.c

+7 −7
Original line number Diff line number Diff line
@@ -54,7 +54,7 @@ static u8 gettime(void) 
	u16 ax = 0x0200;

	u16 cx, dx;



	asm("int $0x1a"

	asm volatile("int $0x1a"

		     : "+a" (ax), "=c" (cx), "=d" (dx)

		     : : "ebx", "esi", "edi");
@@ -67,7 +67,7 @@ static u8 gettime(void) 
int getchar(void)

{

	u16 ax = 0;

	asm("int $0x16" : "+a" (ax));

	asm volatile("int $0x16" : "+a" (ax));



	return ax & 0xff;

}
@@ -75,7 +75,7 @@ int getchar(void) 
static int kbd_pending(void)

{

	u8 pending;

	asm("int $0x16; setnz %0"

	asm volatile("int $0x16; setnz %0"

		     : "=rm" (pending)

		     : "a" (0x0100));

	return pending;

arch/i386/boot/video-vga.c

+6 −6
Original line number Diff line number Diff line
@@ -47,14 +47,14 @@ static u8 vga_set_basic_mode(void) 


#ifdef CONFIG_VIDEO_400_HACK

	if (adapter >= ADAPTER_VGA) {

		asm(INT10

		asm volatile(INT10

			     : : "a" (0x1202), "b" (0x0030)

			     : "ecx", "edx", "esi", "edi");

	}

#endif



	ax = 0x0f00;

	asm(INT10

	asm volatile(INT10

		     : "+a" (ax)

		     : : "ebx", "ecx", "edx", "esi", "edi");

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