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 .text
  14
  15 /*
  16  * Inputs:
  17  * %rsi : memory location to compare
  18  * %rax : low 64 bits of old value
  19  * %rdx : high 64 bits of old value
  20  * %rbx : low 64 bits of new value
  21  * %rcx : high 64 bits of new value
  22  * %al  : Operation successful
  23  */
  24 ENTRY(this_cpu_cmpxchg16b_emu)
  25 CFI_STARTPROC
  26
  27 #
  28 # Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in %al not
  29 # via the ZF.  Caller will access %al to get result.
  30 #
  31 # Note that this is only useful for a cpuops operation.  Meaning that we
  32 # do *not* have a fully atomic operation but just an operation that is
  33 # *atomic* on a single cpu (as provided by the this_cpu_xx class of
  34 # macros).
  35 #
  36 this_cpu_cmpxchg16b_emu:
  37         pushf
  38         cli
  39
  40         cmpq %gs:(%rsi), %rax
  41         jne not_same
  42         cmpq %gs:8(%rsi), %rdx
  43         jne not_same
  44
  45         movq %rbx, %gs:(%rsi)
  46         movq %rcx, %gs:8(%rsi)
  47
  48         popf
  49         mov $1, %al
  50         ret
  51
  52  not_same:
  53         popf
  54         xor %al,%al
  55         ret
  56
  57 CFI_ENDPROC
  58
  59 ENDPROC(this_cpu_cmpxchg16b_emu)