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GCSSS1

GCSSS1, Guarded Control Stack Switch Stack 1

The GCSSS1 characteristics are:

Purpose

Validates that the stack being switched to contains a Valid cap entry, stores an In-progress cap entry on to the stack that is getting switched to and sets the current Guarded Control Stack Pointer to the stack that is getting switched to.

Configuration

This instruction is present only when FEAT_GCS is implemented and FEAT_AA64 is implemented. Otherwise, direct accesses to GCSSS1 are UNDEFINED.

Attributes

GCSSS1 is a 64-bit System instruction.

Field descriptions

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
IA
IA

IA, bits [63:0]

Incoming address, for the incoming Guarded Control Stack.

Executing GCSSS1

This system instruction is an alias of the SYS instruction.

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

GCSSS1 <Xt>

op0	op1	CRn	CRm	op2
0b01	0b011	0b0111	0b0111	0b010

if !(IsFeatureImplemented(FEAT_GCS) && IsFeatureImplemented(FEAT_AA64)) then Undefined(); elsif GCSEnabled(PSTATE.EL) then GCSSS1(X{64}(t)); end;

2026-03-12 12:23:09, 2025-09_rel_asl1

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
IA
IA

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
IA
IA

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
IA
IA