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[Xen-changelog] [xen-3.1-testing] x86: Fix handling of BSF and BSR instructions.

From: "Xen patchbot-3.1-testing" <patchbot-3.1-testing@xxxxxxxxxxxxxxxxxxx>

Date: Tue, 22 Apr 2008 07:11:13 -0700

Delivery-date: Tue, 22 Apr 2008 07:44:02 -0700

List-id: BK change log <xen-changelog.lists.xensource.com>

# HG changeset patch # User Keir Fraser <keir.fraser@xxxxxxxxxx> # Date 1208861932 -3600 # Node ID 22a54b9d88692d11aa1a4de82a09c80146cd0c6b # Parent 563f951a9b1a50a69ae588c9cc16346fcdf543c1 x86: Fix handling of BSF and BSR instructions. 1. We cannot rely on BSF/BSR leaving the destination register intact if the source is zero (according to Intel manuals) 2. We race clear_bit() in find_first_bit(), which may occur after SCAS but before BSF. So we must handle zero input to BSF. Signed-off-by: Naoki Nishiguchi <nisiguti@xxxxxxxxxxxxxx> Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx> xen-unstable changeset: 17495:fec632d30571c40f05e6638477472500ef9cb2c7 xen-unstable date: Tue Apr 22 11:43:10 2008 +0100 --- xen/arch/x86/bitops.c | 36 +++++++++++++++++++----------------- xen/include/asm-x86/bitops.h | 34 ++++++++++++++++------------------ 2 files changed, 35 insertions(+), 35 deletions(-) diff -r 563f951a9b1a -r 22a54b9d8869 xen/arch/x86/bitops.c --- a/xen/arch/x86/bitops.c Tue Apr 22 11:55:29 2008 +0100 +++ b/xen/arch/x86/bitops.c Tue Apr 22 11:58:52 2008 +0100 @@ -7,18 +7,19 @@ unsigned int __find_first_bit( { unsigned long d0, d1, res; - __asm__ __volatile__ ( - " xor %%eax,%%eax\n\t" /* also ensures ZF==1 if size==0 */ + asm volatile ( + "1: xor %%eax,%%eax\n\t" /* also ensures ZF==1 if size==0 */ " repe; scas"__OS"\n\t" - " je 1f\n\t" + " je 2f\n\t" + " bsf -"STR(BITS_PER_LONG/8)"(%2),%0\n\t" + " jz 1b\n\t" " lea -"STR(BITS_PER_LONG/8)"(%2),%2\n\t" - " bsf (%2),%0\n" - "1: sub %%ebx,%%edi\n\t" + "2: sub %%ebx,%%edi\n\t" " shl $3,%%edi\n\t" " add %%edi,%%eax" : "=&a" (res), "=&c" (d0), "=&D" (d1) - : "1" ((size + BITS_PER_LONG - 1) / BITS_PER_LONG), - "2" (addr), "b" ((int)(long)addr) : "memory" ); + : "1" (BITS_TO_LONGS(size)), "2" (addr), "b" ((int)(long)addr) + : "memory" ); return res; } @@ -34,8 +35,7 @@ unsigned int __find_next_bit( if ( bit != 0 ) { /* Look for a bit in the first word. */ - __asm__ ( "bsf %1,%%"__OP"ax" - : "=a" (set) : "r" (*p >> bit), "0" (BITS_PER_LONG) ); + set = __scanbit(*p >> bit, BITS_PER_LONG - bit); if ( set < (BITS_PER_LONG - bit) ) return (offset + set); offset += BITS_PER_LONG - bit; @@ -55,19 +55,21 @@ unsigned int __find_first_zero_bit( { unsigned long d0, d1, d2, res; - __asm__ ( + asm volatile ( + "1: xor %%eax,%%eax ; not %3\n\t" /* rAX == ~0ul */ " xor %%edx,%%edx\n\t" /* also ensures ZF==1 if size==0 */ " repe; scas"__OS"\n\t" - " je 1f\n\t" + " je 2f\n\t" + " xor -"STR(BITS_PER_LONG/8)"(%2),%3\n\t" + " jz 1b\n\t" + " bsf %3,%0\n\t" " lea -"STR(BITS_PER_LONG/8)"(%2),%2\n\t" - " xor (%2),%3\n\t" - " bsf %3,%0\n" - "1: sub %%ebx,%%edi\n\t" + "2: sub %%ebx,%%edi\n\t" " shl $3,%%edi\n\t" " add %%edi,%%edx" : "=&d" (res), "=&c" (d0), "=&D" (d1), "=&a" (d2) - : "1" ((size + BITS_PER_LONG - 1) / BITS_PER_LONG), - "2" (addr), "b" ((int)(long)addr), "3" (-1L) : "memory" ); + : "1" (BITS_TO_LONGS(size)), "2" (addr), "b" ((int)(long)addr) + : "memory" ); return res; } @@ -83,7 +85,7 @@ unsigned int __find_next_zero_bit( if ( bit != 0 ) { /* Look for zero in the first word. */ - __asm__ ( "bsf %1,%%"__OP"ax" : "=a" (set) : "r" (~(*p >> bit)) ); + set = __scanbit(~(*p >> bit), BITS_PER_LONG - bit); if ( set < (BITS_PER_LONG - bit) ) return (offset + set); offset += BITS_PER_LONG - bit; diff -r 563f951a9b1a -r 22a54b9d8869 xen/include/asm-x86/bitops.h --- a/xen/include/asm-x86/bitops.h Tue Apr 22 11:55:29 2008 +0100 +++ b/xen/include/asm-x86/bitops.h Tue Apr 22 11:58:52 2008 +0100 @@ -272,10 +272,9 @@ extern unsigned int __find_next_zero_bit extern unsigned int __find_next_zero_bit( const unsigned long *addr, unsigned int size, unsigned int offset); -/* return index of first bit set in val or BITS_PER_LONG when no bit is set */ -static inline unsigned int __scanbit(unsigned long val) -{ - __asm__ ( "bsf %1,%0" : "=r" (val) : "r" (val), "0" (BITS_PER_LONG) ); +static inline unsigned int __scanbit(unsigned long val, unsigned long max) +{ + asm ( "bsf %1,%0 ; cmovz %2,%0" : "=&r" (val) : "r" (val), "r" (max) ); return (unsigned int)val; } @@ -287,9 +286,9 @@ static inline unsigned int __scanbit(uns * Returns the bit-number of the first set bit, not the number of the byte * containing a bit. */ -#define find_first_bit(addr,size) \ -((__builtin_constant_p(size) && (size) <= BITS_PER_LONG ? \ - (__scanbit(*(const unsigned long *)addr)) : \ +#define find_first_bit(addr,size) \ +((__builtin_constant_p(size) && (size) <= BITS_PER_LONG ? \ + (__scanbit(*(const unsigned long *)addr, size)) : \ __find_first_bit(addr,size))) /** @@ -298,9 +297,9 @@ static inline unsigned int __scanbit(uns * @offset: The bitnumber to start searching at * @size: The maximum size to search */ -#define find_next_bit(addr,size,off) \ -((__builtin_constant_p(size) && (size) <= BITS_PER_LONG ? \ - ((off) + (__scanbit((*(const unsigned long *)addr) >> (off)))) : \ +#define find_next_bit(addr,size,off) \ +((__builtin_constant_p(size) && (size) <= BITS_PER_LONG ? \ + ((off) + (__scanbit((*(const unsigned long *)addr) >> (off), size))) : \ __find_next_bit(addr,size,off))) /** @@ -311,9 +310,9 @@ static inline unsigned int __scanbit(uns * Returns the bit-number of the first zero bit, not the number of the byte * containing a bit. */ -#define find_first_zero_bit(addr,size) \ -((__builtin_constant_p(size) && (size) <= BITS_PER_LONG ? \ - (__scanbit(~*(const unsigned long *)addr)) : \ +#define find_first_zero_bit(addr,size) \ +((__builtin_constant_p(size) && (size) <= BITS_PER_LONG ? \ + (__scanbit(~*(const unsigned long *)addr, size)) : \ __find_first_zero_bit(addr,size))) /** @@ -322,9 +321,9 @@ static inline unsigned int __scanbit(uns * @offset: The bitnumber to start searching at * @size: The maximum size to search */ -#define find_next_zero_bit(addr,size,off) \ -((__builtin_constant_p(size) && (size) <= BITS_PER_LONG ? \ - ((off)+(__scanbit(~(((*(const unsigned long *)addr)) >> (off))))) : \ +#define find_next_zero_bit(addr,size,off) \ +((__builtin_constant_p(size) && (size) <= BITS_PER_LONG ? \ + ((off)+(__scanbit(~(((*(const unsigned long *)addr)) >> (off)), size))) : \ __find_next_zero_bit(addr,size,off))) @@ -332,8 +331,7 @@ static inline unsigned int __scanbit(uns * find_first_set_bit - find the first set bit in @word * @word: the word to search * - * Returns the bit-number of the first set bit. If no bits are set then the - * result is undefined. + * Returns the bit-number of the first set bit. The input must *not* be zero. */ static __inline__ unsigned int find_first_set_bit(unsigned long word) { _______________________________________________ Xen-changelog mailing list Xen-changelog@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-changelog

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