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GCSSS2

GCSSS2, Guarded Control Stack Switch Stack 2

The GCSSS2 characteristics are:

Purpose

Validates that the most recent entry of the Guarded Control Stack that is getting switched to contains an In-progress cap entry, stores a Valid cap entry to the Guarded Control Stack that is getting switched from, and sets Xt to the address of that Valid cap entry.

Configuration

This instruction is present only when FEAT_GCS is implemented and FEAT_AA64 is implemented. Otherwise, direct accesses to GCSSS2 are UNDEFINED.

Attributes

GCSSS2 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
OA
OA

OA, bits [63:0]

Outgoing address, for the outgoing Guarded Control Stack.

Executing GCSSS2

This system instruction is an alias of the SYSL instruction.

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

GCSSS2 <Xt>

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

if !(IsFeatureImplemented(FEAT_GCS) && IsFeatureImplemented(FEAT_AA64)) then Undefined(); elsif GCSEnabled(PSTATE.EL) then X{64}(t) = GCSSS2(); 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
OA
OA

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
OA
OA

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
OA
OA