LXR linux/arch/x86/include/asm/refcount.h

   1#ifndef __ASM_X86_REFCOUNT_H
   2#define __ASM_X86_REFCOUNT_H
   3/*
   4 * x86-specific implementation of refcount_t. Based on PAX_REFCOUNT from
   5 * PaX/grsecurity.
   6 */
   7#include <linux/refcount.h>
   8#include <asm/bug.h>
   9
  10/*
  11 * This is the first portion of the refcount error handling, which lives in
  12 * .text.unlikely, and is jumped to from the CPU flag check (in the
  13 * following macros). This saves the refcount value location into CX for
  14 * the exception handler to use (in mm/extable.c), and then triggers the
  15 * central refcount exception. The fixup address for the exception points
  16 * back to the regular execution flow in .text.
  17 */
  18#define _REFCOUNT_EXCEPTION                             \
  19        ".pushsection .text..refcount\n"                \
  20        "111:\tlea %[counter], %%" _ASM_CX "\n"         \
  21        "112:\t" ASM_UD2 "\n"                           \
  22        ASM_UNREACHABLE                                 \
  23        ".popsection\n"                                 \
  24        "113:\n"                                        \
  25        _ASM_EXTABLE_REFCOUNT(112b, 113b)
  26
  27/* Trigger refcount exception if refcount result is negative. */
  28#define REFCOUNT_CHECK_LT_ZERO                          \
  29        "js 111f\n\t"                                   \
  30        _REFCOUNT_EXCEPTION
  31
  32/* Trigger refcount exception if refcount result is zero or negative. */
  33#define REFCOUNT_CHECK_LE_ZERO                          \
  34        "jz 111f\n\t"                                   \
  35        REFCOUNT_CHECK_LT_ZERO
  36
  37/* Trigger refcount exception unconditionally. */
  38#define REFCOUNT_ERROR                                  \
  39        "jmp 111f\n\t"                                  \
  40        _REFCOUNT_EXCEPTION
  41
  42static __always_inline void refcount_add(unsigned int i, refcount_t *r)
  43{
  44        asm volatile(LOCK_PREFIX "addl %1,%0\n\t"
  45                REFCOUNT_CHECK_LT_ZERO
  46                : [counter] "+m" (r->refs.counter)
  47                : "ir" (i)
  48                : "cc", "cx");
  49}
  50
  51static __always_inline void refcount_inc(refcount_t *r)
  52{
  53        asm volatile(LOCK_PREFIX "incl %0\n\t"
  54                REFCOUNT_CHECK_LT_ZERO
  55                : [counter] "+m" (r->refs.counter)
  56                : : "cc", "cx");
  57}
  58
  59static __always_inline void refcount_dec(refcount_t *r)
  60{
  61        asm volatile(LOCK_PREFIX "decl %0\n\t"
  62                REFCOUNT_CHECK_LE_ZERO
  63                : [counter] "+m" (r->refs.counter)
  64                : : "cc", "cx");
  65}
  66
  67static __always_inline __must_check
  68bool refcount_sub_and_test(unsigned int i, refcount_t *r)
  69{
  70        GEN_BINARY_SUFFIXED_RMWcc(LOCK_PREFIX "subl", REFCOUNT_CHECK_LT_ZERO,
  71                                  r->refs.counter, "er", i, "%0", e, "cx");
  72}
  73
  74static __always_inline __must_check bool refcount_dec_and_test(refcount_t *r)
  75{
  76        GEN_UNARY_SUFFIXED_RMWcc(LOCK_PREFIX "decl", REFCOUNT_CHECK_LT_ZERO,
  77                                 r->refs.counter, "%0", e, "cx");
  78}
  79
  80static __always_inline __must_check
  81bool refcount_add_not_zero(unsigned int i, refcount_t *r)
  82{
  83        int c, result;
  84
  85        c = atomic_read(&(r->refs));
  86        do {
  87                if (unlikely(c == 0))
  88                        return false;
  89
  90                result = c + i;
  91
  92                /* Did we try to increment from/to an undesirable state? */
  93                if (unlikely(c < 0 || c == INT_MAX || result < c)) {
  94                        asm volatile(REFCOUNT_ERROR
  95                                     : : [counter] "m" (r->refs.counter)
  96                                     : "cc", "cx");
  97                        break;
  98                }
  99
 100        } while (!atomic_try_cmpxchg(&(r->refs), &c, result));
 101
 102        return c != 0;
 103}
 104
 105static __always_inline __must_check bool refcount_inc_not_zero(refcount_t *r)
 106{
 107        return refcount_add_not_zero(1, r);
 108}
 109
 110#endif
 111