MRS Move Special register to general-purpose register Move Special register to general-purpose register moves the value of the APSR, CPSR, or SPSR_<current_mode> into a general-purpose register. Arm recommends the APSR form when only the N, Z, C, V, Q, and GE[3:0] bits are being written. For more information, see APSR. An MRS that accesses the SPSRs is unpredictable if executed in User mode or System mode. An MRS that is executed in User mode and accesses the CPSR returns an unknown value for the CPSR.{E, A, I, F, M} fields. For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors. It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) . != 1111 0 0 0 1 0 0 0 (1) (1) (1) (1) (0) (0) 0 (0) 0 0 0 0 (0) (0) (0) (0) MRS{<c>}{<q>} <Rd>, <spec_reg> d = UInt(Rd); read_spsr = (R == '1'); if d == 15 then UNPREDICTABLE; 1 1 1 1 0 0 1 1 1 1 1 (1) (1) (1) (1) 1 0 (0) 0 (0) (0) 0 (0) (0) (0) (0) (0) MRS{<c>}{<q>} <Rd>, <spec_reg> d = UInt(Rd); read_spsr = (R == '1'); if d == 15 then UNPREDICTABLE; // Armv8-A removes UNPREDICTABLE for R13 <c> See Standard assembler syntax fields. <q> See Standard assembler syntax fields. <Rd> Is the general-purpose destination register, encoded in the "Rd" field. <spec_reg> Is the special register to be accessed, R <spec_reg> 0 CPSR|APSR 1 SPSR if ConditionPassed() then EncodingSpecificOperations(); if read_spsr then if PSTATE.M IN {M32_User,M32_System} then UNPREDICTABLE; else R[d] = SPSR[]; else // CPSR has same bit assignments as SPSR, but with the IT, J, SS, IL, and T bits masked out. bits(32) mask = '11111000 11101111 00000011 11011111'; psr_val = GetPSRFromPSTATE(AArch32_NonDebugState, 32) AND mask; if PSTATE.EL == EL0 then // If accessed from User mode return UNKNOWN values for E, A, I, F bits, bits<9:6>, // and for the M field, bits<4:0> psr_val<22> = bits(1) UNKNOWN; psr_val<9:6> = bits(4) UNKNOWN; psr_val<4:0> = bits(5) UNKNOWN; R[d] = psr_val; PSTATE.M IN {M32_User, M32_System} && read_spsr