ArmPkg/Library/ArmSvcLib/Arm/ArmSvc.S

   1 //
   2 //  Copyright (c) 2016 - 2020, ARM Limited. All rights reserved.
   3 //
   4 //  SPDX-License-Identifier: BSD-2-Clause-Patent
   5 //
   6 //
   7
   8 .text
   9 .align 3
  10
  11 GCC_ASM_EXPORT(ArmCallSvc)
  12
  13 ASM_PFX(ArmCallSvc):
  14     // r0 will be popped just after the SVC call
  15     push    {r0, r4-r8}
  16
  17     // Load the SVC arguments values into the appropriate registers
  18     ldm     r0, {r0-r7}
  19
  20     svc     #0
  21     // Prevent speculative execution beyond svc instruction
  22     dsb     nsh
  23     isb
  24
  25     // Load the ARM_SVC_ARGS structure address from the stack into r8
  26     ldr     r8, [sp]
  27
  28     // Load the SVC returned values into the appropriate registers
  29     // A SVC call can return up to 4 values - we do not need to store back r4-r7.
  30     stm     r8, {r0-r3}
  31
  32     mov     r0, r8
  33
  34     // Restore the registers r4-r8
  35     pop     {r1, r4-r8}
  36     bx      lr