SPSR_und

AArch64 System register SPSR_und bits [31:0] are architecturally mapped to AArch32 System register SPSR_und[31:0].

If EL1 only supports execution in AArch64 state, this register is RES0 from EL2 and EL3.

Attributes

Field descriptions

When EL1 can only use AArch64:

Bits [63:0]

Otherwise:

Bits [63:32]

N, bit [31]

Negative Condition flag. Set to the value of PSTATE.N on taking an exception to Undefined mode, and copied to PSTATE.N on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Z, bit [30]

Zero Condition flag. Set to the value of PSTATE.Z on taking an exception to Undefined mode, and copied to PSTATE.Z on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

C, bit [29]

Carry Condition flag. Set to the value of PSTATE.C on taking an exception to Undefined mode, and copied to PSTATE.C on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

V, bit [28]

Overflow Condition flag. Set to the value of PSTATE.V on taking an exception to Undefined mode, and copied to PSTATE.V on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Q, bit [27]

Overflow or saturation flag. Set to the value of PSTATE.Q on taking an exception to Undefined mode, and copied to PSTATE.Q on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

IT, bits [15:10, 26:25]

If-Then. Set to the value of PSTATE.IT on taking an exception to Undefined mode, and copied to PSTATE.IT on executing an illegal exception return operation in Undefined mode.

SPSR_und.IT must contain a value that is valid for the instruction being returned to.

The IT field is split as follows:

IT[1:0] is SPSR_und[26:25].
IT[7:2] is SPSR_und[15:10].

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

J, bit [24]

RES0.

In previous versions of the architecture, the {J, T} bits determined the AArch32 Instruction set state.

Armv8 does not support either Jazelle state or T32EE state, and the T bit determines the Instruction set state.

SSBS, bit [23]
When FEAT_SSBS is implemented:

Speculative Store Bypass. Set to the value of PSTATE.SSBS on taking an exception to Undefined mode, and copied to PSTATE.SSBS on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Otherwise:

PAN, bit [22]
When FEAT_PAN is implemented:

Privileged Access Never. Set to the value of PSTATE.PAN on taking an exception to Undefined mode, and copied to PSTATE.PAN on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Otherwise:

DIT, bit [21]
When FEAT_DIT is implemented:

Data Independent Timing. Set to the value of PSTATE.DIT on taking an exception to Undefined mode, and copied to PSTATE.DIT on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Otherwise:

IL, bit [20]

Illegal Execution state. Set to the value of PSTATE.IL on taking an exception to Undefined mode, and copied to PSTATE.IL on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

GE, bits [19:16]

Greater than or Equal flags. Set to the value of PSTATE.GE on taking an exception to Undefined mode, and copied to PSTATE.GE on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

E, bit [9]

Endianness. Set to the value of PSTATE.E on taking an exception to Undefined mode, and copied to PSTATE.E on executing an illegal exception return operation in Undefined mode.

If the implementation does not support big-endian operation, SPSR_und.E is RES0. If the implementation does not support little-endian operation, SPSR_und.E is RES1. On executing an illegal exception return operation in Undefined mode, if the implementation does not support big-endian operation at the Exception level being returned to, SPSR_und.E is RES0, and if the implementation does not support little-endian operation at the Exception level being returned to, SPSR_und.E is RES1.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

A, bit [8]

SError exception mask. Set to the value of PSTATE.A on taking an exception to Undefined mode, and copied to PSTATE.A on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

I, bit [7]

IRQ interrupt mask. Set to the value of PSTATE.I on taking an exception to Undefined mode, and copied to PSTATE.I on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

F, bit [6]

FIQ interrupt mask. Set to the value of PSTATE.F on taking an exception to Undefined mode, and copied to PSTATE.F on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

T, bit [5]

T32 Instruction set state. Set to the value of PSTATE.T on taking an exception to Undefined mode, and copied to PSTATE.T on executing an illegal exception return operation in Undefined mode.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

M[4:0], bits [4:0]

Mode. Set to the value of PSTATE.M[4:0] on taking an exception to Undefined mode, and copied to PSTATE.M[4:0] on executing an illegal exception return operation in Undefined mode.

M[4:0]	Meaning
0b10000	User.
0b10001	FIQ.
0b10010	IRQ.
0b10011	Supervisor.
0b10111	Abort.
0b11011	Undefined.
0b11111	System.

Other values are reserved. If SPSR_und.M[4:0] has a Reserved value, or a value for an unimplemented Exception level, executing an illegal exception return operation in Undefined mode is an illegal return event, as described in 'Illegal return events from AArch32 state'.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Accessing SPSR_und

Accesses to this register use the following encodings in the System register encoding space:

MRS <Xt>, SPSR_und

op0	op1	CRn	CRm	op2
0b11	0b100	0b0100	0b0011	0b010

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then X[t, 64] = SPSR_und; elsif PSTATE.EL == EL3 then X[t, 64] = SPSR_und;

MSR SPSR_und, <Xt>

op0	op1	CRn	CRm	op2
0b11	0b100	0b0100	0b0011	0b010

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then SPSR_und = X[t, 64]; elsif PSTATE.EL == EL3 then SPSR_und = X[t, 64];

63	62	61	60	59	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44	43	42	41	40	39	38	37	36	35	34	33	32
31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
RES0
RES0

63	62	61	60	59	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44	43	42	41	40	39	38	37	36	35	34	33	32
31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
RES0
N	Z	C	V	Q	IT[1:0]		J	SSBS	PAN	DIT	IL	GE				IT[7:2]						E	A	I	F	T	M[4:0]

SPSR_und, Saved Program Status Register (Undefined mode)

Purpose

Configuration

Attributes

Field descriptions

When EL1 can only use AArch64:

Bits [63:0]

Otherwise:

Bits [63:32]

N, bit [31]

Z, bit [30]

C, bit [29]

V, bit [28]

Q, bit [27]

IT, bits [15:10, 26:25]

J, bit [24]

SSBS, bit [23]
When FEAT_SSBS is implemented:

Otherwise:

PAN, bit [22]
When FEAT_PAN is implemented:

Otherwise:

DIT, bit [21]
When FEAT_DIT is implemented:

Otherwise:

IL, bit [20]

GE, bits [19:16]

E, bit [9]

A, bit [8]

I, bit [7]

F, bit [6]

T, bit [5]

M[4:0], bits [4:0]

Accessing SPSR_und

MRS <Xt>, SPSR_und

MSR SPSR_und, <Xt>

SPSR_und, Saved Program Status Register (Undefined mode)

Purpose

Configuration

Attributes

Field descriptions

When EL1 can only use AArch64:

Bits [63:0]

Otherwise:

Bits [63:32]

N, bit [31]

Z, bit [30]

C, bit [29]

V, bit [28]

Q, bit [27]

IT, bits [15:10, 26:25]

J, bit [24]

SSBS, bit [23]When FEAT_SSBS is implemented:

Otherwise:

PAN, bit [22]When FEAT_PAN is implemented:

Otherwise:

DIT, bit [21]When FEAT_DIT is implemented:

Otherwise:

IL, bit [20]

GE, bits [19:16]

E, bit [9]

A, bit [8]

I, bit [7]

F, bit [6]

T, bit [5]

M[4:0], bits [4:0]

Accessing SPSR_und

MRS <Xt>, SPSR_und

MSR SPSR_und, <Xt>

SSBS, bit [23]
When FEAT_SSBS is implemented:

PAN, bit [22]
When FEAT_PAN is implemented:

DIT, bit [21]
When FEAT_DIT is implemented: