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CONTEXTIDR_EL1, Context ID Register (EL1)

The CONTEXTIDR_EL1 characteristics are:

Purpose

Identifies the current Process Identifier.

The value of the whole of this register is called the Context ID and is used by:

  • The debug logic, for Linked and Unlinked Context ID matching.
  • The trace logic, to identify the current process.

The significance of this register is for debug and trace use only.

This register is used when ARMv8.1-VHE is not implemented, or whenARMv8.1-VHE is implemented and HCR_EL2.E2H is set to 0.

Note

When ARMv8.1-VHE is implemented and HCR_EL2.E2H is set to 1, CONTEXTIDR_EL2 is used.

Configuration

AArch64 System register CONTEXTIDR_EL1 bits [31:0] are architecturally mapped to AArch32 System register CONTEXTIDR[31:0] .

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

CONTEXTIDR_EL1 is a 64-bit register.

Field descriptions

The CONTEXTIDR_EL1 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
RES0
PROCID
313029282726252423222120191817161514131211109876543210

Bits [63:32]

Reserved, RES0.

PROCID, bits [31:0]

Process Identifier. This field must be programmed with a unique value that identifies the current process.

Note

In AArch32 state, when TTBCR.EAE is set to 0, CONTEXTIDR.ASID holds the ASID.

In AArch64 state, CONTEXTIDR_EL1 is independent of the ASID, and for the EL1&0 translation regime either TTBR0_EL1 or TTBR1_EL1 holds the ASID.

This field resets to an architecturally UNKNOWN value.

Accessing the CONTEXTIDR_EL1

When HCR_EL2.E2H is 1, without explicit synchronization, access from EL3 using the mnemonic CONTEXTIDR_EL1 or CONTEXTIDR_EL12 are not guaranteed to be ordered with respect to accesses using the other mnemonic.

Accesses to this register use the following encodings:

MRS <Xt>, CONTEXTIDR_EL1

op0op1CRnCRmop2
0b110b0000b11010b00000b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TRVM == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<NV2,NV1,NV> == '111' then
        return NVMem[0x108];
    else
        return CONTEXTIDR_EL1;
elsif PSTATE.EL == EL2 then
    if HCR_EL2.E2H == '1' then
        return CONTEXTIDR_EL2;
    else
        return CONTEXTIDR_EL1;
elsif PSTATE.EL == EL3 then
    return CONTEXTIDR_EL1;
              

MSR CONTEXTIDR_EL1, <Xt>

op0op1CRnCRmop2
0b110b0000b11010b00000b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TVM == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<NV2,NV1,NV> == '111' then
        NVMem[0x108] = X[t];
    else
        CONTEXTIDR_EL1 = X[t];
elsif PSTATE.EL == EL2 then
    if HCR_EL2.E2H == '1' then
        CONTEXTIDR_EL2 = X[t];
    else
        CONTEXTIDR_EL1 = X[t];
elsif PSTATE.EL == EL3 then
    CONTEXTIDR_EL1 = X[t];
              

MRS <Xt>, CONTEXTIDR_EL12

op0op1CRnCRmop2
0b110b1010b11010b00000b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.<NV2,NV1,NV> == '101' then
        return NVMem[0x108];
    elsif EL2Enabled() && HCR_EL2.NV == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    if EL2Enabled() && HCR_EL2.E2H == '1' then
        return CONTEXTIDR_EL1;
    else
        UNDEFINED;
elsif PSTATE.EL == EL3 then
    if EL2Enabled() && HCR_EL2.E2H == '1' then
        return CONTEXTIDR_EL1;
    else
        UNDEFINED;
              

MSR CONTEXTIDR_EL12, <Xt>

op0op1CRnCRmop2
0b110b1010b11010b00000b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.<NV2,NV1,NV> == '101' then
        NVMem[0x108] = X[t];
    elsif EL2Enabled() && HCR_EL2.NV == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    if EL2Enabled() && HCR_EL2.E2H == '1' then
        CONTEXTIDR_EL1 = X[t];
    else
        UNDEFINED;
elsif PSTATE.EL == EL3 then
    if EL2Enabled() && HCR_EL2.E2H == '1' then
        CONTEXTIDR_EL1 = X[t];
    else
        UNDEFINED;
              


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