arch/x86/lib/cmpxchg16b_emu.S

   1 /*
   2  *      This program is free software; you can redistribute it and/or
   3  *      modify it under the terms of the GNU General Public License
   4  *      as published by the Free Software Foundation; version 2
   5  *      of the License.
   6  *
   7  */
   8 #include <linux/linkage.h>
   9 #include <asm/alternative-asm.h>
  10 #include <asm/frame.h>
  11 #include <asm/dwarf2.h>
  12
  13 #ifdef CONFIG_SMP
  14 #define SEG_PREFIX %gs:
  15 #else
  16 #define SEG_PREFIX
  17 #endif
  18
  19 .text
  20
  21 /*
  22  * Inputs:
  23  * %rsi : memory location to compare
  24  * %rax : low 64 bits of old value
  25  * %rdx : high 64 bits of old value
  26  * %rbx : low 64 bits of new value
  27  * %rcx : high 64 bits of new value
  28  * %al  : Operation successful
  29  */
  30 ENTRY(this_cpu_cmpxchg16b_emu)
  31 CFI_STARTPROC
  32
  33 #
  34 # Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in %al not
  35 # via the ZF.  Caller will access %al to get result.
  36 #
  37 # Note that this is only useful for a cpuops operation.  Meaning that we
  38 # do *not* have a fully atomic operation but just an operation that is
  39 # *atomic* on a single cpu (as provided by the this_cpu_xx class of
  40 # macros).
  41 #
  42 this_cpu_cmpxchg16b_emu:
  43         pushf
  44         cli
  45
  46         cmpq SEG_PREFIX(%rsi), %rax
  47         jne not_same
  48         cmpq SEG_PREFIX 8(%rsi), %rdx
  49         jne not_same
  50
  51         movq %rbx, SEG_PREFIX(%rsi)
  52         movq %rcx, SEG_PREFIX 8(%rsi)
  53
  54         popf
  55         mov $1, %al
  56         ret
  57
  58  not_same:
  59         popf
  60         xor %al,%al
  61         ret
  62
  63 CFI_ENDPROC
  64
  65 ENDPROC(this_cpu_cmpxchg16b_emu)