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/percpu.h>
  10
  11 .text
  12
  13 /*
  14  * Inputs:
  15  * %rsi : memory location to compare
  16  * %rax : low 64 bits of old value
  17  * %rdx : high 64 bits of old value
  18  * %rbx : low 64 bits of new value
  19  * %rcx : high 64 bits of new value
  20  * %al  : Operation successful
  21  */
  22 ENTRY(this_cpu_cmpxchg16b_emu)
  23
  24 #
  25 # Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in %al not
  26 # via the ZF.  Caller will access %al to get result.
  27 #
  28 # Note that this is only useful for a cpuops operation.  Meaning that we
  29 # do *not* have a fully atomic operation but just an operation that is
  30 # *atomic* on a single cpu (as provided by the this_cpu_xx class of
  31 # macros).
  32 #
  33         pushfq
  34         cli
  35
  36         cmpq PER_CPU_VAR((%rsi)), %rax
  37         jne .Lnot_same
  38         cmpq PER_CPU_VAR(8(%rsi)), %rdx
  39         jne .Lnot_same
  40
  41         movq %rbx, PER_CPU_VAR((%rsi))
  42         movq %rcx, PER_CPU_VAR(8(%rsi))
  43
  44         popfq
  45         mov $1, %al
  46         ret
  47
  48 .Lnot_same:
  49         popfq
  50         xor %al,%al
  51         ret
  52
  53 ENDPROC(this_cpu_cmpxchg16b_emu)