arch/all-mingw32/kernel/leaveinterrupt_x86_64.s

   1 #
   2 #   Copyright © 2010-2011, The AROS Development Team. All rights reserved.
   3 #   $Id$
   4 #
   5 #   Desc: Exit from emulated interrupt with enabling, x86-64 version
   6 #   Lang: English
   7 #
   8
   9 # Theory of operation:
  10 # x86-64 has red zone of 128 bytes below the rsp. This makes it impossible to use
  11 # push/pop instructions here, unlike on i386, because doing this will destroy
  12 # red zone data.
  13 # Here we skip the red zone and use -128(%rsp) as our intermediate storage. However,
  14 # there's an important problem with this. x86 is not ARM, and we can't do something like
  15 # "addq $128, %rsp; jmpq *-128(rsp)" atomically. This mean, we can be preempted right before
  16 # the final jump. This is dangerous, because next time we will get back here with our own
  17 # address in 0(%rax), overwriting -128(rsp) with it and causing infinite loop.
  18 # In order to work around this issue, interrupt thread checks rip value, and if rip is
  19 # pointing at this code, interrupts are considered disabled.
  20 # We still have to use stack for temporary storage because we first need to restore rax
  21 # and only then jump to return address.
  22
  23         .globl  core_LeaveInterrupt
  24         .globl  core_LeaveInt_End
  25
  26 core_LeaveInterrupt:
  27         movq    %rbx, -128(%rsp)    # Save rbx
  28         movq    0(%rax), %rbx       # Get real return address into rbx
  29         xchg    %rbx, -128(%rsp)    # Remember return address and restore rbx
  30         movq    8(%rax), %rax       # Restore real rax contents
  31         movl    $1, Ints_Enabled    # Now enable interrupts
  32         jmpq    *-128(%rsp)         # And jump to the needed address
  33 core_LeaveInt_End: