Release 4.14 arch/x86/include/asm/refcount.h
#ifndef __ASM_X86_REFCOUNT_H
#define __ASM_X86_REFCOUNT_H
/*
* x86-specific implementation of refcount_t. Based on PAX_REFCOUNT from
* PaX/grsecurity.
*/
#include <linux/refcount.h>
/*
* This is the first portion of the refcount error handling, which lives in
* .text.unlikely, and is jumped to from the CPU flag check (in the
* following macros). This saves the refcount value location into CX for
* the exception handler to use (in mm/extable.c), and then triggers the
* central refcount exception. The fixup address for the exception points
* back to the regular execution flow in .text.
*/
#define _REFCOUNT_EXCEPTION \
".pushsection .text.unlikely\n" \
"111:\tlea %[counter], %%" _ASM_CX "\n" \
"112:\t" ASM_UD0 "\n" \
ASM_UNREACHABLE \
".popsection\n" \
"113:\n" \
_ASM_EXTABLE_REFCOUNT(112b, 113b)
/* Trigger refcount exception if refcount result is negative. */
#define REFCOUNT_CHECK_LT_ZERO \
"js 111f\n\t" \
_REFCOUNT_EXCEPTION
/* Trigger refcount exception if refcount result is zero or negative. */
#define REFCOUNT_CHECK_LE_ZERO \
"jz 111f\n\t" \
REFCOUNT_CHECK_LT_ZERO
/* Trigger refcount exception unconditionally. */
#define REFCOUNT_ERROR \
"jmp 111f\n\t" \
_REFCOUNT_EXCEPTION
static __always_inline void refcount_add(unsigned int i, refcount_t *r)
{
asm volatile(LOCK_PREFIX "addl %1,%0\n\t"
REFCOUNT_CHECK_LT_ZERO
: [counter] "+m" (r->refs.counter)
: "ir" (i)
: "cc", "cx");
}
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static __always_inline void refcount_inc(refcount_t *r)
{
asm volatile(LOCK_PREFIX "incl %0\n\t"
REFCOUNT_CHECK_LT_ZERO
: [counter] "+m" (r->refs.counter)
: : "cc", "cx");
}
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static __always_inline void refcount_dec(refcount_t *r)
{
asm volatile(LOCK_PREFIX "decl %0\n\t"
REFCOUNT_CHECK_LE_ZERO
: [counter] "+m" (r->refs.counter)
: : "cc", "cx");
}
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static __always_inline __must_check
bool refcount_sub_and_test(unsigned int i, refcount_t *r)
{
GEN_BINARY_SUFFIXED_RMWcc(LOCK_PREFIX "subl", REFCOUNT_CHECK_LT_ZERO,
r->refs.counter, "er", i, "%0", e);
}
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static __always_inline __must_check bool refcount_dec_and_test(refcount_t *r)
{
GEN_UNARY_SUFFIXED_RMWcc(LOCK_PREFIX "decl", REFCOUNT_CHECK_LT_ZERO,
r->refs.counter, "%0", e);
}
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static __always_inline __must_check
bool refcount_add_not_zero(unsigned int i, refcount_t *r)
{
int c, result;
c = atomic_read(&(r->refs));
do {
if (unlikely(c == 0))
return false;
result = c + i;
/* Did we try to increment from/to an undesirable state? */
if (unlikely(c < 0 || c == INT_MAX || result < c)) {
asm volatile(REFCOUNT_ERROR
: : [counter] "m" (r->refs.counter)
: "cc", "cx");
break;
}
} while (!atomic_try_cmpxchg(&(r->refs), &c, result));
return c != 0;
}
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static __always_inline __must_check bool refcount_inc_not_zero(refcount_t *r)
{
return refcount_add_not_zero(1, r);
}
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#endif
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