smc

Secure Monitor Call (A32)

SMC<c> #<imm>

Calls the Secure Monitor (EL3).

Details

Secure Monitor Call: a synchronous exception that transitions execution to the Secure Monitor at EL3 to handle a secure service request. The immediate value encodes the SMC ID for the handler. This instruction requires Secure state; execution in Non-secure state is subject to the SMCNC trap. Subject to condition code in A32.

Pseudocode Operation

exception_taken ← 'SMC'
ELR_EL3 ← PC + 4
SPSR_EL3 ← CPSR
CPSR.M ← '10110' (Monitor mode)
PC ← VECTOR_SMC

Example

SMC #16

Encoding

Binary Layout

cond

00010

000000000000

0111

imm4

Format System

Opcode 0x01600070

Extension A32 (System)

Operands

imm
ID

Reference (Arm AArch32 ISA)

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x01600070	SMC{<c>}{<q>} {#}<imm4>		A32		cond \| 00010 \| 11 \| 0 \| 000000000000 \| 0111 \| imm4
0xF7F08000	SMC{<c>}{<q>} {#}<imm4>		T32		11110111111 \| 1 \| imm4 \| 10 \| 0 \| 0 \| 000000000000

Description

Secure Monitor Call causes a Secure Monitor Call exception. For more information see Secure Monitor Call (SMC) exception. SMC is available only for software executing at EL1 or higher. It is undefined in User mode. If the values of HCR.TSC and SCR.SCD are both 0, execution of an SMC instruction at EL1 or higher generates a Secure Monitor Call exception that is taken to EL3. When EL3 is using AArch32 this exception is taken to Monitor mode. When EL3 is using AArch64, it is the SCR_EL3.SMD bit, rather than the SCR.SCD bit, that can change the effect of executing an SMC instruction. If the value of HCR.TSC is 1, execution of an SMC instruction in a Non-secure EL1 mode generates an exception that is taken to EL2, regardless of the value of SCR.SCD. When EL2 is using AArch32, this is a Hyp Trap exception that is taken to Hyp mode. For more information see Traps to Hyp mode of Non-secure EL1 execution of SMC instructions. If the value of HCR.TSC is 0 and the value of SCR.SCD is 1, the SMC instruction is:

Operation

if ConditionPassed() then
    EncodingSpecificOperations();

    AArch32.CheckForSMCUndefOrTrap();

    if !ELUsingAArch32(EL3) then
        if SCR_EL3.SMD == '1' then
            // SMC disabled.
            UNDEFINED;
    else
        if SCR.SCD == '1' then
            // SMC disabled
            if CurrentSecurityState() == SS_Secure then
                // Executes either as a NOP or UNALLOCATED.
                c = ConstrainUnpredictable(Unpredictable_SMD);
                assert c IN {Constraint_NOP, Constraint_UNDEF};
                if c == Constraint_NOP then EndOfInstruction();
            UNDEFINED;

    if !ELUsingAArch32(EL3) then
        AArch64.CallSecureMonitor(Zeros(16));
    else
        AArch32.TakeSMCException();