The ELR_EL2 characteristics are:
When taking an exception to EL2, holds the address to return to.
AArch64 System register ELR_EL2 bits [31:0] are architecturally mapped to AArch32 System register ELR_hyp[31:0].
This register has no effect if EL2 is not enabled in the current Security state.
ELR_EL2 is a 64-bit register.
| 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 |
| Return address | |||||||||||||||||||||||||||||||
| Return address | |||||||||||||||||||||||||||||||
Return address.
An exception return from EL2 using AArch64 makes ELR_EL2 become UNKNOWN.
When EL2 is in AArch32 Execution state and an exception is taken from EL0, EL1, or EL2 to EL3 and AArch64 execution, the upper 32-bits of ELR_EL2 are either set to 0 or hold the same value that they did before AArch32 execution. Which option is adopted is determined by an implementation, and might vary dynamically within an implementation. Correspondingly software must regard the value as being an UNKNOWN choice between the two values.
The reset behavior of this field is:
When HCR_EL2.E2H is 1, without explicit synchronization, access from EL2 using the mnemonic ELR_EL2 or ELR_EL1 are not guaranteed to be ordered with respect to accesses using the other mnemonic.
Accesses to this register use the following encodings in the System register encoding space:
| op0 | op1 | CRn | CRm | op2 |
|---|---|---|---|---|
| 0b11 | 0b100 | 0b0100 | 0b0000 | 0b001 |
if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && HCR_EL2.<NV2,NV> == '11' then X[t, 64] = ELR_EL1; elsif EL2Enabled() && HCR_EL2.NV == '1' then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then X[t, 64] = ELR_EL2; elsif PSTATE.EL == EL3 then X[t, 64] = ELR_EL2;
| op0 | op1 | CRn | CRm | op2 |
|---|---|---|---|---|
| 0b11 | 0b100 | 0b0100 | 0b0000 | 0b001 |
if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if IsFeatureImplemented(FEAT_GCS) && GetCurrentEXLOCKEN() && !Halted() && PSTATE.EXLOCK == '1' && EL2Enabled() && HCR_EL2.NV == '1' then EXLOCKException(); elsif EL2Enabled() && HCR_EL2.<NV2,NV> == '11' then ELR_EL1 = X[t, 64]; elsif EL2Enabled() && HCR_EL2.NV == '1' then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then if IsFeatureImplemented(FEAT_GCS) && GetCurrentEXLOCKEN() && !Halted() && PSTATE.EXLOCK == '1' then EXLOCKException(); else ELR_EL2 = X[t, 64]; elsif PSTATE.EL == EL3 then ELR_EL2 = X[t, 64];
| op0 | op1 | CRn | CRm | op2 |
|---|---|---|---|---|
| 0b11 | 0b000 | 0b0100 | 0b0000 | 0b001 |
if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && HCR_EL2.<NV2,NV1,NV> == '011' then AArch64.SystemAccessTrap(EL2, 0x18); elsif EL2Enabled() && HCR_EL2.<NV2,NV1,NV> == '111' then X[t, 64] = NVMem[0x230]; else X[t, 64] = ELR_EL1; elsif PSTATE.EL == EL2 then if HCR_EL2.E2H == '1' then X[t, 64] = ELR_EL2; else X[t, 64] = ELR_EL1; elsif PSTATE.EL == EL3 then X[t, 64] = ELR_EL1;
| op0 | op1 | CRn | CRm | op2 |
|---|---|---|---|---|
| 0b11 | 0b000 | 0b0100 | 0b0000 | 0b001 |
if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if IsFeatureImplemented(FEAT_GCS) && GetCurrentEXLOCKEN() && !Halted() && PSTATE.EXLOCK == '1' && (HCR_EL2.NV == '0' || (EL2Enabled() && HCR_EL2.<NV1,NV> == '01')) then EXLOCKException(); elsif EL2Enabled() && HCR_EL2.<NV2,NV1,NV> == '011' then AArch64.SystemAccessTrap(EL2, 0x18); elsif EL2Enabled() && HCR_EL2.<NV2,NV1,NV> == '111' then NVMem[0x230] = X[t, 64]; else ELR_EL1 = X[t, 64]; elsif PSTATE.EL == EL2 then if IsFeatureImplemented(FEAT_GCS) && GetCurrentEXLOCKEN() && !Halted() && PSTATE.EXLOCK == '1' && HCR_EL2.E2H == '1' then EXLOCKException(); elsif HCR_EL2.E2H == '1' then ELR_EL2 = X[t, 64]; else ELR_EL1 = X[t, 64]; elsif PSTATE.EL == EL3 then ELR_EL1 = X[t, 64];
04/07/2023 11:24; 1b994cb0b8c6d1ae5a9a15edbc8bd6ce3b5c7d68
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