ArmPkg/ArmSvcLib: prevent speculative execution beyond svc

[mirror_edk2.git] / ArmPkg / Library / ArmSvcLib / Arm / ArmSvc.asm

//\r
//  Copyright (c) 2016 - 2020, ARM Limited. All rights reserved.\r
//\r
//  SPDX-License-Identifier: BSD-2-Clause-Patent\r
//\r
//\r
\r
\r
    INCLUDE AsmMacroExport.inc\r
\r
 RVCT_ASM_EXPORT ArmCallSvc\r
    // r0 will be popped just after the SVC call\r
    push     {r0, r4-r8}\r
\r
    // Load the SVC arguments values into the appropriate registers\r
    ldm     r0, {r0-r7}\r
\r
    svc     #0\r
    // Prevent speculative execution beyond svc instruction\r
    dsb     nsh\r
    isb\r
\r
    // Load the ARM_SVC_ARGS structure address from the stack into r8\r
    ldr     r8, [sp]\r
\r
    // Load the SVC returned values into the appropriate registers\r
    // A SVC call can return up to 4 values - we do not need to store back r4-r7.\r
    stm     r8, {r0-r3}\r
\r
    mov     r0, r8\r
\r
    // Restore the registers r4-r8\r
    pop     {r1, r4-r8}\r
    bx      lr\r
\r
    END\r