kern/arch/x86/bitops.h

#pragma once

/*
 * Copyright 1992, Linus Torvalds.
 *
 * Note: inlines with more than a single statement should be marked
 * __always_inline to avoid problems with older gcc's inlining heuristics.
 */

#define BIT_64(n)			(U64_C(1) << (n))
#define DECLARE_BITMAP(name,bits) \
	unsigned long name[(bits+sizeof(unsigned long)*8 - 1)/(sizeof(unsigned long)*8)/*BITS_TO_LONGS(bits)*/]
/*
 * These have to be done with inline assembly: that way the bit-setting
 * is guaranteed to be atomic. All bit operations return 0 if the bit
 * was cleared before the operation and != 0 if it was not.
 *
 * bit 0 is the LSB of addr; bit 32 is the LSB of (addr+1).
 */

#if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 1)
#error "Get a gcc newer than 4.4.0"
#else
#define BITOP_ADDR(x) "+m" (*(volatile long *) (x))
#endif

#define ADDR				BITOP_ADDR(addr)

#define LOCK_PREFIX "lock "
/*
 * We do the locked ops that don't return the old value as
 * a mask operation on a byte.
 */
#define IS_IMMEDIATE(nr)		(__builtin_constant_p(nr))
#define CONST_MASK_ADDR(nr, addr)	BITOP_ADDR((void *)(addr) + ((nr)>>3))
#define CONST_MASK(nr)			(1 << ((nr) & 7))

/**
 * set_bit - Atomically set a bit in memory
 * @nr: the bit to set
 * @addr: the address to start counting from
 *
 * This function is atomic and may not be reordered.  See __set_bit()
 * if you do not require the atomic guarantees.
 *
 * Note: there are no guarantees that this function will not be reordered
 * on non x86 architectures, so if you are writing portable code,
 * make sure not to rely on its reordering guarantees.
 *
 * Note that @nr may be almost arbitrarily large; this function is not
 * restricted to acting on a single-word quantity.
 */
static __always_inline void
set_bit(unsigned int nr, volatile unsigned long *addr)
{
	if (IS_IMMEDIATE(nr)) {
		asm volatile(LOCK_PREFIX "orb %1,%0"
			: CONST_MASK_ADDR(nr, addr)
			: "iq" ((uint8_t)CONST_MASK(nr))
			: "memory");
	} else {
		asm volatile(LOCK_PREFIX "bts %1,%0"
			: BITOP_ADDR(addr) : "Ir" (nr) : "memory");
	}
}

/**
 * __set_bit - Set a bit in memory
 * @nr: the bit to set
 * @addr: the address to start counting from
 *
 * Unlike set_bit(), this function is non-atomic and may be reordered.
 * If it's called on the same region of memory simultaneously, the effect
 * may be that only one operation succeeds.
 */
static inline void __set_bit(int nr, volatile unsigned long *addr)
{
	asm volatile("bts %1,%0" : ADDR : "Ir" (nr) : "memory");
}

/**
 * clear_bit - Clears a bit in memory
 * @nr: Bit to clear
 * @addr: Address to start counting from
 *
 * clear_bit() is atomic and may not be reordered.  However, it does
 * not contain a memory barrier, so if it is used for locking purposes,
 * you should call smp_mb__before_clear_bit() and/or smp_mb__after_clear_bit()
 * in order to ensure changes are visible on other processors.
 *
 * Note from brho: I think the use of LOCK_PREFIX (assuming it is "lock")
 * provides a memory barrier against hardware reordering accesses around the
 * LOCK ("lock" serializes).  This lacks a cmb() (called a barrier() in Linux),
 * which would prevent the compiler from reordering the instructions.  The
 * above-mentioned smp_mb__before_clear_bit appears to be this cmb(), so it's
 * not clear what the usage of "memory barrier" means exactly here and
 * elsewhere in this file. */
static __always_inline void
clear_bit(int nr, volatile unsigned long *addr)
{
	if (IS_IMMEDIATE(nr)) {
		asm volatile(LOCK_PREFIX "andb %1,%0"
			: CONST_MASK_ADDR(nr, addr)
			: "iq" ((uint8_t)~CONST_MASK(nr)));
	} else {
		asm volatile(LOCK_PREFIX "btr %1,%0"
			: BITOP_ADDR(addr)
			: "Ir" (nr));
	}
}

/*
 * clear_bit_unlock - Clears a bit in memory
 * @nr: Bit to clear
 * @addr: Address to start counting from
 *
 * clear_bit() is atomic and implies release semantics before the memory
 * operation. It can be used for an unlock.
 */
static inline void clear_bit_unlock(unsigned nr, volatile unsigned long *addr)
{
	cmb();
	clear_bit(nr, addr);
}

static inline void __clear_bit(int nr, volatile unsigned long *addr)
{
	asm volatile("btr %1,%0" : ADDR : "Ir" (nr));
}

/*
 * __clear_bit_unlock - Clears a bit in memory
 * @nr: Bit to clear
 * @addr: Address to start counting from
 *
 * __clear_bit() is non-atomic and implies release semantics before the memory
 * operation. It can be used for an unlock if no other CPUs can concurrently
 * modify other bits in the word.
 *
 * No memory barrier is required here, because x86 cannot reorder stores past
 * older loads. Same principle as spin_unlock.
 */
static inline void __clear_bit_unlock(unsigned nr, volatile unsigned long *addr)
{
	cmb();
	__clear_bit(nr, addr);
}

#define smp_mb__before_clear_bit()	cmb()
#define smp_mb__after_clear_bit()	cmb()

/**
 * __change_bit - Toggle a bit in memory
 * @nr: the bit to change
 * @addr: the address to start counting from
 *
 * Unlike change_bit(), this function is non-atomic and may be reordered.
 * If it's called on the same region of memory simultaneously, the effect
 * may be that only one operation succeeds.
 */
static inline void __change_bit(int nr, volatile unsigned long *addr)
{
	asm volatile("btc %1,%0" : ADDR : "Ir" (nr));
}

/**
 * change_bit - Toggle a bit in memory
 * @nr: Bit to change
 * @addr: Address to start counting from
 *
 * change_bit() is atomic and may not be reordered.
 * Note that @nr may be almost arbitrarily large; this function is not
 * restricted to acting on a single-word quantity.
 */
static inline void change_bit(int nr, volatile unsigned long *addr)
{
	if (IS_IMMEDIATE(nr)) {
		asm volatile(LOCK_PREFIX "xorb %1,%0"
			: CONST_MASK_ADDR(nr, addr)
			: "iq" ((uint8_t)CONST_MASK(nr)));
	} else {
		asm volatile(LOCK_PREFIX "btc %1,%0"
			: BITOP_ADDR(addr)
			: "Ir" (nr));
	}
}

/**
 * test_and_set_bit - Set a bit and return its old value
 * @nr: Bit to set
 * @addr: Address to count from
 *
 * This operation is atomic and cannot be reordered.
 * It also implies a memory barrier.
 */
static inline int test_and_set_bit(int nr, volatile unsigned long *addr)
{
	int oldbit;

	asm volatile(LOCK_PREFIX "bts %2,%1\n\t"
		     "sbb %0,%0" : "=r" (oldbit), ADDR : "Ir" (nr) : "memory");

	return oldbit;
}

/**
 * test_and_set_bit_lock - Set a bit and return its old value for lock
 * @nr: Bit to set
 * @addr: Address to count from
 *
 * This is the same as test_and_set_bit on x86.
 */
static __always_inline int
test_and_set_bit_lock(int nr, volatile unsigned long *addr)
{
	return test_and_set_bit(nr, addr);
}

/**
 * __test_and_set_bit - Set a bit and return its old value
 * @nr: Bit to set
 * @addr: Address to count from
 *
 * This operation is non-atomic and can be reordered.
 * If two examples of this operation race, one can appear to succeed
 * but actually fail.  You must protect multiple accesses with a lock.
 */
static inline int __test_and_set_bit(int nr, volatile unsigned long *addr)
{
	int oldbit;

	asm("bts %2,%1\n\t"
	    "sbb %0,%0"
	    : "=r" (oldbit), ADDR
	    : "Ir" (nr));
	return oldbit;
}

/**
 * test_and_clear_bit - Clear a bit and return its old value
 * @nr: Bit to clear
 * @addr: Address to count from
 *
 * This operation is atomic and cannot be reordered.
 * It also implies a memory barrier.
 */
static inline int test_and_clear_bit(int nr, volatile unsigned long *addr)
{
	int oldbit;

	asm volatile(LOCK_PREFIX "btr %2,%1\n\t"
		     "sbb %0,%0"
		     : "=r" (oldbit), ADDR : "Ir" (nr) : "memory");

	return oldbit;
}

/**
 * __test_and_clear_bit - Clear a bit and return its old value
 * @nr: Bit to clear
 * @addr: Address to count from
 *
 * This operation is non-atomic and can be reordered.
 * If two examples of this operation race, one can appear to succeed
 * but actually fail.  You must protect multiple accesses with a lock.
 *
 * Note: the operation is performed atomically with respect to
 * the local CPU, but not other CPUs. Portable code should not
 * rely on this behaviour.
 * KVM relies on this behaviour on x86 for modifying memory that is also
 * accessed from a hypervisor on the same CPU if running in a VM: don't change
 * this without also updating arch/x86/kernel/kvm.c
 */
static inline int __test_and_clear_bit(int nr, volatile unsigned long *addr)
{
	int oldbit;

	asm volatile("btr %2,%1\n\t"
		     "sbb %0,%0"
		     : "=r" (oldbit), ADDR
		     : "Ir" (nr));
	return oldbit;
}

/* WARNING: non atomic and it can be reordered! */
static inline int __test_and_change_bit(int nr, volatile unsigned long *addr)
{
	int oldbit;

	asm volatile("btc %2,%1\n\t"
		     "sbb %0,%0"
		     : "=r" (oldbit), ADDR
		     : "Ir" (nr) : "memory");

	return oldbit;
}

/**
 * test_and_change_bit - Change a bit and return its old value
 * @nr: Bit to change
 * @addr: Address to count from
 *
 * This operation is atomic and cannot be reordered.
 * It also implies a memory barrier.
 */
static inline int test_and_change_bit(int nr, volatile unsigned long *addr)
{
	int oldbit;

	asm volatile(LOCK_PREFIX "btc %2,%1\n\t"
		     "sbb %0,%0"
		     : "=r" (oldbit), ADDR : "Ir" (nr) : "memory");

	return oldbit;
}

static __always_inline int constant_test_bit(unsigned int nr, const volatile unsigned long *addr)
{
	return ((1UL << (nr % BITS_PER_LONG)) &
		(addr[nr / BITS_PER_LONG])) != 0;
}

static inline int variable_test_bit(int nr, volatile const unsigned long *addr)
{
	int oldbit;

	asm volatile("bt %2,%1\n\t"
		     "sbb %0,%0"
		     : "=r" (oldbit)
		     : "m" (*(unsigned long *)addr), "Ir" (nr));

	return oldbit;
}

#define test_bit(nr, addr)                      \
        (__builtin_constant_p((nr))             \
         ? constant_test_bit((nr), (addr))      \
         : variable_test_bit((nr), (addr)))
/**
 * __ffs - find first set bit in word
 * @word: The word to search
 *
 * Undefined if no bit exists, so code should check against 0 first.
 */
static inline unsigned long __ffs(unsigned long word)
{
	asm("rep; bsf %1,%0"
		: "=r" (word)
		: "rm" (word));
	return word;
}

/**
 * ffz - find first zero bit in word
 * @word: The word to search
 *
 * Undefined if no zero exists, so code should check against ~0UL first.
 */
static inline unsigned long ffz(unsigned long word)
{
	asm("rep; bsf %1,%0"
		: "=r" (word)
		: "r" (~word));
	return word;
}

/*
 * __fls: find last set bit in word
 * @word: The word to search
 *
 * Undefined if no set bit exists, so code should check against 0 first.
 */
static inline unsigned long __fls(unsigned long word)
{
	asm("bsr %1,%0"
	    : "=r" (word)
	    : "rm" (word));
	return word;
}

#undef ADDR

/**
 * ffs - find first set bit in word
 * @x: the word to search
 *
 * This is defined the same way as the libc and compiler builtin ffs
 * routines, therefore differs in spirit from the other bitops.
 *
 * ffs(value) returns 0 if value is 0 or the position of the first
 * set bit if value is nonzero. The first (least significant) bit
 * is at position 1.
 */
static inline int ffs(int x)
{
	int r;

	/*
	 * AMD64 says BSFL won't clobber the dest reg if x==0; Intel64 says the
	 * dest reg is undefined if x==0, but their CPU architect says its
	 * value is written to set it to the same as before, except that the
	 * top 32 bits will be cleared.
	 *
	 * We cannot do this on 32 bits because at the very least some
	 * 486 CPUs did not behave this way.
	 */
	asm("bsfl %1,%0"
	    : "=r" (r)
	    : "rm" (x), "0" (-1));
	return r + 1;
}

/**
 * fls - find last set bit in word
 * @x: the word to search
 *
 * This is defined in a similar way as the libc and compiler builtin
 * ffs, but returns the position of the most significant set bit.
 *
 * fls(value) returns 0 if value is 0 or the position of the last
 * set bit if value is nonzero. The last (most significant) bit is
 * at position 32.
 */
static inline int fls(int x)
{
	int r;

	/*
	 * AMD64 says BSRL won't clobber the dest reg if x==0; Intel64 says the
	 * dest reg is undefined if x==0, but their CPU architect says its
	 * value is written to set it to the same as before, except that the
	 * top 32 bits will be cleared.
	 *
	 * We cannot do this on 32 bits because at the very least some
	 * 486 CPUs did not behave this way.
	 */
	asm("bsrl %1,%0"
	    : "=r" (r)
	    : "rm" (x), "0" (-1));
	return r + 1;
}

/**
 * fls64 - find last set bit in a 64-bit word
 * @x: the word to search
 *
 * This is defined in a similar way as the libc and compiler builtin
 * ffsll, but returns the position of the most significant set bit.
 *
 * fls64(value) returns 0 if value is 0 or the position of the last
 * set bit if value is nonzero. The last (most significant) bit is
 * at position 64.
 */
static __always_inline int fls64(uint64_t x)
{
	int bitpos = -1;
	/*
	 * AMD64 says BSRQ won't clobber the dest reg if x==0; Intel64 says the
	 * dest reg is undefined if x==0, but their CPU architect says its
	 * value is written to set it to the same as before.
	 */
	asm("bsrq %1,%q0"
	    : "+r" (bitpos)
	    : "rm" (x));
	return bitpos + 1;
}