x86_64/pthreads/preempt.s

   1 /*
   2  * Copyright (c) 2002 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 #include <machine/cpu_capabilities.h>
  25 #include <mach/i386/syscall_sw.h>
  26
  27 /* Subroutine to make a preempt syscall.  Called when we notice %ebx is
  28  * nonzero after returning from a PFZ subroutine.  Not in PFZ.
  29  *
  30  * All registers preserved (but does clear the %ebx preemption flag).
  31  */
  32         .align 2
  33         .private_extern _preempt
  34 _preempt:
  35         pushq   %rax
  36         pushq   %rcx
  37         pushq   %r11
  38         movl    $(SYSCALL_CONSTRUCT_MACH(58)),%eax      /* 58 = pfz_exit */
  39         xorl    %ebx,%ebx
  40         syscall
  41         popq    %r11
  42         popq    %rcx
  43         popq    %rax
  44         ret
  45
  46 /* Subroutine to back off if we cannot get the spinlock.  Called
  47  * after a few attempts inline in the PFZ subroutines.  This code is
  48  * not in the PFZ.
  49  *      %rdi = ptr to queue head structure
  50  *      %ebx = preemption flag (nonzero if preemption pending)
  51  * Uses: %rax.
  52  */
  53         .align 2
  54         .private_extern _backoff
  55 _backoff:
  56         testl   %ebx,%ebx       // does kernel want to preempt us?
  57         jz      1f              // no
  58         call    _preempt
  59 1:
  60         pause                   // SMT-friendly backoff
  61         cmpl    $0,16(%rdi)     // sniff the lockword
  62         jnz     1b              // loop if still taken
  63         ret                     // lockword is free, so reenter PFZ