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RGSR_EL1

RGSR_EL1, Random Allocation Tag Seed Register.

The RGSR_EL1 characteristics are:

Purpose

Random Allocation Tag Seed Register.

Configuration

This register is present only when FEAT_MTE2 is implemented. Otherwise, direct accesses to RGSR_EL1 are UNDEFINED.

When GCR_EL1.RRND==0b1, updates to RGSR_EL1 are implementation-specific.

Direct and indirect reads and writes to the register appear to occur in program order relative to other instructions, without the need for any explicit synchronization.

Attributes

RGSR_EL1 is a 64-bit register.

Field descriptions

When GCR_EL1.RRND == 0:

6362616059585756555453525150494847464544434241403938373635343332
313029282726252423222120191817161514131211109876543210
RES0
RES0SEEDRES0TAG

Bits [63:24]

Reserved, RES0.

SEED, bits [23:8]

Seed register used for generating values returned by RandomTag().

The reset behavior of this field is:

Bits [7:4]

Reserved, RES0.

TAG, bits [3:0]

Tag generated by the most recent IRG instruction.

The reset behavior of this field is:

Otherwise:

6362616059585756555453525150494847464544434241403938373635343332
313029282726252423222120191817161514131211109876543210
RES0SEED
SEEDRES0TAG

Bits [63:56]

Reserved, RES0.

SEED, bits [55:8]

IMPLEMENTATION DEFINED.

Note

Software is recommended to avoid writing SEED[15:0] with a value of zero, unless this has been generated by the PE in response to an earlier value with SEED being nonzero.

The reset behavior of this field is:

Bits [7:4]

Reserved, RES0.

TAG, bits [3:0]

IMPLEMENTATION DEFINED.

The reset behavior of this field is:

Accessing RGSR_EL1

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

MRS <Xt>, RGSR_EL1

op0op1CRnCRmop2
0b110b0000b00010b00000b101

if !IsFeatureImplemented(FEAT_MTE2) then Undefined(); elsif PSTATE.EL == EL0 then Undefined(); elsif PSTATE.EL == EL1 then if HaveEL(EL3) && EL3SDDUndefPriority() && !(IsFeatureImplemented(FEAT_MTE2) && SCR_EL3().ATA == '1') then Undefined(); elsif EL2Enabled() && !ELIsInHost(EL0) && !(IsFeatureImplemented(FEAT_MTE2) && HCR_EL2().ATA == '1') then AArch64_SystemAccessTrap(EL2, 0x18); elsif HaveEL(EL3) && !(IsFeatureImplemented(FEAT_MTE2) && SCR_EL3().ATA == '1') then if EL3SDDUndef() then Undefined(); else AArch64_SystemAccessTrap(EL3, 0x18); end; else X{64}(t) = RGSR_EL1(); end; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && EL3SDDUndefPriority() && !(IsFeatureImplemented(FEAT_MTE2) && SCR_EL3().ATA == '1') then Undefined(); elsif HaveEL(EL3) && !(IsFeatureImplemented(FEAT_MTE2) && SCR_EL3().ATA == '1') then if EL3SDDUndef() then Undefined(); else AArch64_SystemAccessTrap(EL3, 0x18); end; else X{64}(t) = RGSR_EL1(); end; elsif PSTATE.EL == EL3 then X{64}(t) = RGSR_EL1(); end;

MSR RGSR_EL1, <Xt>

op0op1CRnCRmop2
0b110b0000b00010b00000b101

if !IsFeatureImplemented(FEAT_MTE2) then Undefined(); elsif PSTATE.EL == EL0 then Undefined(); elsif PSTATE.EL == EL1 then if HaveEL(EL3) && EL3SDDUndefPriority() && !(IsFeatureImplemented(FEAT_MTE2) && SCR_EL3().ATA == '1') then Undefined(); elsif EL2Enabled() && !ELIsInHost(EL0) && !(IsFeatureImplemented(FEAT_MTE2) && HCR_EL2().ATA == '1') then AArch64_SystemAccessTrap(EL2, 0x18); elsif HaveEL(EL3) && !(IsFeatureImplemented(FEAT_MTE2) && SCR_EL3().ATA == '1') then if EL3SDDUndef() then Undefined(); else AArch64_SystemAccessTrap(EL3, 0x18); end; else RGSR_EL1() = X{64}(t); end; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && EL3SDDUndefPriority() && !(IsFeatureImplemented(FEAT_MTE2) && SCR_EL3().ATA == '1') then Undefined(); elsif HaveEL(EL3) && !(IsFeatureImplemented(FEAT_MTE2) && SCR_EL3().ATA == '1') then if EL3SDDUndef() then Undefined(); else AArch64_SystemAccessTrap(EL3, 0x18); end; else RGSR_EL1() = X{64}(t); end; elsif PSTATE.EL == EL3 then RGSR_EL1() = X{64}(t); end;


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

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