Arm® A64 Instruction Set Architecture: Armv8, for Armv8-A architecture profile

Library pseudocode for aarch64/instrs/branch/eret/AArch64.ExceptionReturn

// AArch64.ExceptionReturn()
// =========================

AArch64.ExceptionReturn(bits(64) new_pc, bits(32) spsr)

    SynchronizeContext();

    sync_errors = HaveIESB() && SCTLR[].IESB == '1';
    if HaveDoubleFaultExt() then
        sync_errors = sync_errors || (SCR_EL3.EA == '1' && SCR_EL3.NMEA == '1' && PSTATE.EL == EL3);
    if sync_errors then
        SynchronizeErrors();
        iesb_req = TRUE;
        TakeUnmaskedPhysicalSErrorInterrupts(iesb_req);
    // Attempts to change to an illegal state will invoke the Illegal Execution state mechanism
    SetPSTATEFromPSR(spsr);
    ClearExclusiveLocal(ProcessorID());
    SendEventLocal();

    if PSTATE.IL == '1' && spsr<4> == '1' && spsr<20> == '0' then
        // If the exception return is illegal, PC[63:32,1:0] are UNKNOWN
        new_pc<63:32> = bits(32) UNKNOWN;
        new_pc<1:0> = bits(2) UNKNOWN;
    elsif UsingAArch32() then                // Return to AArch32
        // ELR_ELx[1:0] or ELR_ELx[0] are treated as being 0, depending on the target instruction set state
        if PSTATE.T == '1' then
            new_pc<0> = '0';                 // T32
        else
            new_pc<1:0> = '00';              // A32
    else                                     // Return to AArch64
        // ELR_ELx[63:56] might include a tag
        new_pc = AArch64.BranchAddr(new_pc);

    if UsingAArch32() then
        // 32 most significant bits are ignored.
        BranchTo(new_pc<31:0>, BranchType_ERET);
    else
        BranchToAddr(new_pc, BranchType_ERET);