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SCXTNUM_EL3
AArch32 Registers
AArch64 Registers
AArch32 Instructions
AArch64 Instructions
Index by Encoding
External Registers
External Registers by Offset
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Proprietary Notice

SCXTNUM_EL3, EL3 Read/Write Software Context Number

The SCXTNUM_EL3 characteristics are:

Purpose

Provides a number that can be used to separate out different context numbers with the EL3 exception level, for the purpose of protecting against side-channels using branch prediction and similar resources.

Configuration

This register is present only when EL3 is implemented, (FEAT_CSV2_2 is implemented or FEAT_CSV2_1p2 is implemented), and FEAT_AA64 is implemented. Otherwise, direct accesses to SCXTNUM_EL3 are UNDEFINED.

Attributes

SCXTNUM_EL3 is a 64-bit register.

Field descriptions

6362616059585756555453525150494847464544434241403938373635343332
313029282726252423222120191817161514131211109876543210
SCXTNUM
SCXTNUM

SCXTNUM, bits [63:0]

Software Context Number. A number to identify the context within the EL3 exception level.

The reset behavior of this field is:

Accessing SCXTNUM_EL3

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

MRS <Xt>, SCXTNUM_EL3

op0op1CRnCRmop2
0b110b1100b11010b00000b111

if !(HaveEL(EL3) && (IsFeatureImplemented(FEAT_CSV2_2) || IsFeatureImplemented(FEAT_CSV2_1p2)) && IsFeatureImplemented(FEAT_AA64)) then Undefined(); elsif PSTATE.EL == EL0 then Undefined(); elsif PSTATE.EL == EL1 then Undefined(); elsif PSTATE.EL == EL2 then Undefined(); elsif PSTATE.EL == EL3 then X{64}(t) = SCXTNUM_EL3(); end;

MSR SCXTNUM_EL3, <Xt>

op0op1CRnCRmop2
0b110b1100b11010b00000b111

if !(HaveEL(EL3) && (IsFeatureImplemented(FEAT_CSV2_2) || IsFeatureImplemented(FEAT_CSV2_1p2)) && IsFeatureImplemented(FEAT_AA64)) then Undefined(); elsif PSTATE.EL == EL0 then Undefined(); elsif PSTATE.EL == EL1 then Undefined(); elsif PSTATE.EL == EL2 then Undefined(); elsif PSTATE.EL == EL3 then SCXTNUM_EL3() = X{64}(t); end;

AArch32 Registers
AArch64 Registers
AArch32 Instructions
AArch64 Instructions
Index by Encoding
External Registers
External Registers by Offset
Registers by Functional Group
Proprietary Notice

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

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