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Commit 06024f21 authored by Alexandre Oliva's avatar Alexandre Oliva Committed by Linus Torvalds
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[PATCH] x86-64: bitops fix for -Os 



This fixes the x86-64 find_[first|next]_zero_bit() function for the
end-of-range case.  It didn't test for a zero size, and the "rep scas"
would do entirely the wrong thing.

Signed-off-by: default avatarAlexandre Oliva <oliva@lsd.ic.unicamp.br>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent cfa024f4

arch/x86_64/lib/bitops.c

+50 −16
Original line number Diff line number Diff line
@@ -5,19 +5,23 @@ 
#undef find_first_bit

#undef find_next_bit



/**

 * find_first_zero_bit - find the first zero bit in a memory region

 * @addr: The address to start the search at

 * @size: The maximum size to search

 *

 * Returns the bit-number of the first zero bit, not the number of the byte

 * containing a bit.

 */

inline long find_first_zero_bit(const unsigned long * addr, unsigned long size)

static inline long

__find_first_zero_bit(const unsigned long * addr, unsigned long size)

{

	long d0, d1, d2;

	long res;



	/*

	 * We must test the size in words, not in bits, because

	 * otherwise incoming sizes in the range -63..-1 will not run

	 * any scasq instructions, and then the flags used by the je

	 * instruction will have whatever random value was in place

	 * before.  Nobody should call us like that, but

	 * find_next_zero_bit() does when offset and size are at the

	 * same word and it fails to find a zero itself.

	 */

	size += 63;

	size >>= 6;

	if (!size)

		return 0;

	asm volatile(
@@ -30,11 +34,29 @@ inline long find_first_zero_bit(const unsigned long * addr, unsigned long size) 
		"  shlq $3,%%rdi\n"

		"  addq %%rdi,%%rdx"

		:"=d" (res), "=&c" (d0), "=&D" (d1), "=&a" (d2)

		:"0" (0ULL), "1" ((size + 63) >> 6), "2" (addr), "3" (-1ULL),

		 [addr] "r" (addr) : "memory");

		:"0" (0ULL), "1" (size), "2" (addr), "3" (-1ULL),

		 [addr] "S" (addr) : "memory");

	/*

	 * Any register would do for [addr] above, but GCC tends to

	 * prefer rbx over rsi, even though rsi is readily available

	 * and doesn't have to be saved.

	 */

	return res;

}



/**

 * find_first_zero_bit - find the first zero bit in a memory region

 * @addr: The address to start the search at

 * @size: The maximum size to search

 *

 * Returns the bit-number of the first zero bit, not the number of the byte

 * containing a bit.

 */

long find_first_zero_bit(const unsigned long * addr, unsigned long size)

{

	return __find_first_zero_bit (addr, size);

}



/**

 * find_next_zero_bit - find the first zero bit in a memory region

 * @addr: The address to base the search on
@@ -43,7 +65,7 @@ inline long find_first_zero_bit(const unsigned long * addr, unsigned long size) 
 */

long find_next_zero_bit (const unsigned long * addr, long size, long offset)

{

	unsigned long * p = ((unsigned long *) addr) + (offset >> 6);

	const unsigned long * p = addr + (offset >> 6);

	unsigned long set = 0;

	unsigned long res, bit = offset&63;
@@ -63,8 +85,8 @@ long find_next_zero_bit (const unsigned long * addr, long size, long offset) 
	/*

	 * No zero yet, search remaining full words for a zero

	 */

	res = find_first_zero_bit ((const unsigned long *)p,

				   size - 64 * (p - (unsigned long *) addr));

	res = __find_first_zero_bit (p, size - 64 * (p - addr));



	return (offset + set + res);

}
@@ -74,6 +96,19 @@ __find_first_bit(const unsigned long * addr, unsigned long size) 
	long d0, d1;

	long res;



	/*

	 * We must test the size in words, not in bits, because

	 * otherwise incoming sizes in the range -63..-1 will not run

	 * any scasq instructions, and then the flags used by the jz

	 * instruction will have whatever random value was in place

	 * before.  Nobody should call us like that, but

	 * find_next_bit() does when offset and size are at the same

	 * word and it fails to find a one itself.

	 */

	size += 63;

	size >>= 6;

	if (!size)

		return 0;

	asm volatile(

		"   repe; scasq\n"

		"   jz 1f\n"
@@ -83,8 +118,7 @@ __find_first_bit(const unsigned long * addr, unsigned long size) 
		"   shlq $3,%%rdi\n"

		"   addq %%rdi,%%rax"

		:"=a" (res), "=&c" (d0), "=&D" (d1)

		:"0" (0ULL),

		 "1" ((size + 63) >> 6), "2" (addr),

		:"0" (0ULL), "1" (size), "2" (addr),

		 [addr] "r" (addr) : "memory");

	return res;

}