EOR, EORS (register) -- AArch32

Bitwise Exclusive-OR (register) performs a bitwise exclusive-OR of a register value and an optionally-shifted register value, and writes the result to the destination register.

If the destination register is not the PC, the EORS variant of the instruction updates the condition flags based on the result.

The field descriptions for <Rd> identify the encodings where the PC is permitted as the destination register. Arm deprecates any use of these encodings. However, when the destination register is the PC:

It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 and T2 ) .

EOR, shift or rotate by value (S == 0 && !(imm5 == 00000 && stype == 11))

EOR{<c>}{<q>} {<Rd>,} <Rn>, <Rm> {, <shift> #<amount>}

EORS, shift or rotate by value (S == 1 && !(imm5 == 00000 && stype == 11))

EORS{<c>}{<q>} {<Rd>,} <Rn>, <Rm> {, <shift> #<amount>}

constant d = UInt(Rd); constant n = UInt(Rn); constant m = UInt(Rm); constant setflags = (S == '1'); constant (shift_t, shift_n) = DecodeImmShift(stype, imm5);

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	1	0	0	0	0	0	0	0	1	Rm	Rdn

T1

EOR <c>{<q>} {<Rdn>,} <Rdn>, <Rm> // (Inside IT block)

EORS{<q>} {<Rdn>,} <Rdn>, <Rm> // (Outside IT block)

constant d = UInt(Rdn); constant n = UInt(Rdn); constant m = UInt(Rm); constant setflags = !InITBlock(); constant (shift_t, shift_n) = (SRType_LSL, 0);

EOR, shift or rotate by value (S == 0 && !(imm3 == 000 && imm2 == 00 && stype == 11))

EOR <c>.W {<Rd>,} <Rn>, <Rm> // (Inside IT block, and <Rd>, <Rn>, <Rm> can be represented in T1)

EOR{<c>}{<q>} {<Rd>,} <Rn>, <Rm> {, <shift> #<amount>}

EORS, rotate right with extend (S == 1 && imm3 == 000 && Rd != 1111 && imm2 == 00 && stype == 11)

EORS{<c>}{<q>} {<Rd>,} <Rn>, <Rm>, RRX

EORS, shift or rotate by value (S == 1 && !(imm3 == 000 && imm2 == 00 && stype == 11) && Rd != 1111)

EORS.W {<Rd>,} <Rn>, <Rm> // (Outside IT block, and <Rd>, <Rn>, <Rm> can be represented in T1)

EORS{<c>}{<q>} {<Rd>,} <Rn>, <Rm> {, <shift> #<amount>}

if Rd == '1111' && S == '1' then SEE "TEQ (register)"; constant d = UInt(Rd); constant n = UInt(Rn); constant m = UInt(Rm); constant setflags = (S == '1'); constant (shift_t, shift_n) = DecodeImmShift(stype, imm3:imm2); // Armv8-A removes UNPREDICTABLE for R13 if (d == 15 && !setflags) || n == 15 || m == 15 then UNPREDICTABLE;

For more information about the constrained unpredictable behavior, see Architectural Constraints on UNPREDICTABLE behaviors.

Assembler Symbols

<c>	See Standard assembler syntax fields.

<q>	See Standard assembler syntax fields.

<Rdn>

Is the first general-purpose source register and the destination register, encoded in the "Rdn" field.

<Rd>

For encoding A1: is the general-purpose destination register, encoded in the "Rd" field. If omitted, this register is the same as <Rn>. Arm deprecates using the PC as the destination register, but if the PC is used:

For the EOR variant, the instruction is a branch to the address calculated by the operation. This is an interworking branch, see Pseudocode description of operations on the AArch32 general-purpose registers and the PC.
For the EORS variant, the instruction performs an exception return, that restores PSTATE from SPSR_<current_mode>.

For encoding T2: is the general-purpose destination register, encoded in the "Rd" field. If omitted, this register is the same as <Rn>.

<Rn>	For encoding A1: is the first general-purpose source register, encoded in the "Rn" field. The PC can be used, but this is deprecated.
	For encoding T2: is the first general-purpose source register, encoded in the "Rn" field.

<Rm>	For encoding A1: is the second general-purpose source register, encoded in the "Rm" field. The PC can be used, but this is deprecated.
	For encoding T1 and T2: is the second general-purpose source register, encoded in the "Rm" field.

<shift>

Is the type of shift to be applied to the second source register, encoded in stype:

stype	<shift>
00	LSL
01	LSR
10	ASR
11	ROR

<amount>	For encoding A1: is the shift amount, in the range 1 to 31 (when <shift> = LSL or ROR) or 1 to 32 (when <shift> = LSR or ASR) encoded in the "imm5" field as <amount> modulo 32.
	For encoding T2: is the shift amount, in the range 1 to 31 (when <shift> = LSL or ROR) or 1 to 32 (when <shift> = LSR or ASR), encoded in the "imm3:imm2" field as <amount> modulo 32.

In T32 assembly:

Outside an IT block, if EORS <Rd>, <Rn>, <Rd> has <Rd> and <Rn> both in the range R0-R7, it is assembled using encoding T1 as though EORS <Rd>, <Rn> had been written
Inside an IT block, if EOR<c> <Rd>, <Rn>, <Rd> has <Rd> and <Rn> both in the range R0-R7, it is assembled using encoding T1 as though EOR<c> <Rd>, <Rn> had been written.

To prevent either of these happening, use the .W qualifier.

Operation

if ConditionPassed() then EncodingSpecificOperations(); constant (shifted, carry) = Shift_C(R[m], shift_t, shift_n, PSTATE.C); constant result = R[n] EOR shifted; if d == 15 then // Can only occur for A32 encoding if setflags then ALUExceptionReturn(result); else ALUWritePC(result); else R[d] = result; if setflags then PSTATE.N = result<31>; PSTATE.Z = IsZeroBit(result); PSTATE.C = carry; // PSTATE.V unchanged

Operational information

If CPSR.DIT is 1 and this instruction does not use R15 as either its source or destination:

Internal version only: isa v01_31, pseudocode v2024-03_rel ; Build timestamp: 2024-03-25T10:05