ArmPkg/Library/SemihostLib/Arm/GccSemihost.S

   1 #------------------------------------------------------------------------------
   2 #
   3 # Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR>
   4 #
   5 # This program and the accompanying materials
   6 # are licensed and made available under the terms and conditions of the BSD License
   7 # which accompanies this distribution.  The full text of the license may be found at
   8 # http://opensource.org/licenses/bsd-license.php
   9 #
  10 # THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  11 # WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  12 #
  13 #------------------------------------------------------------------------------
  14
  15 .text
  16 .align 2
  17
  18 .globl ASM_PFX(GccSemihostCall)
  19 INTERWORK_FUNC(GccSemihostCall)
  20
  21 /*
  22   Semihosting operation request mechanism
  23
  24   SVC  0x123456  in ARM state (for all architectures)
  25   SVC  0xAB in Thumb state (excluding ARMv7-M)
  26   BKPT 0xAB for ARMv7-M (Thumb-2 only)
  27
  28   R0 - operation type
  29   R1 - block containing all other parametes
  30
  31   lr - must be saved as svc instruction will cause an svc exception and write
  32        the svc lr register. That happens to be the one we are using, so we must
  33        save it or we will not be able to return.
  34  */
  35 ASM_PFX(GccSemihostCall):
  36   stmfd   sp!, {lr}
  37   svc     #0x123456
  38   ldmfd   sp!, {lr}
  39   bx      lr
  40
  41