Exception Link Register (EL2)
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 is present only when FEAT_AA64 is implemented. Otherwise, direct accesses to ELR_EL2 are UNDEFINED.
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 |
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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 the Effective value of HCR_EL2.E2H is 1, without explicit synchronization, accesses from EL2 using the accessor name ELR_EL2 or ELR_EL1 are not guaranteed to be ordered with respect to accesses using the other accessor name.
Accesses to this register use the following encodings in the System register encoding space:
MRS <Xt>, ELR_EL2
(op0 = 0b11, op1 = 0b100, CRn = 0b0100, CRm = 0b0000, op2 = 0b001)
if !IsFeatureImplemented(FEAT_AA64) then UNDEFINED; elsif PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'1x1'} then X[t, 64] = ELR_EL1; elsif EffectiveHCR_EL2_NVx() IN {'xx1'} 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;
MSR ELR_EL2, <Xt>
(op0 = 0b11, op1 = 0b100, CRn = 0b0100, CRm = 0b0000, op2 = 0b001)
if !IsFeatureImplemented(FEAT_AA64) then UNDEFINED; elsif PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if IsFeatureImplemented(FEAT_GCS) && GetCurrentEXLOCKEN() && !Halted() && PSTATE.EXLOCK == '1' && EffectiveHCR_EL2_NVx() IN {'xx1'} then EXLOCKException(); elsif EffectiveHCR_EL2_NVx() IN {'1x1'} then ELR_EL1 = X[t, 64]; elsif EffectiveHCR_EL2_NVx() IN {'xx1'} 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];
MRS <Xt>, ELR_EL1
(op0 = 0b11, op1 = 0b000, CRn = 0b0100, CRm = 0b0000, op2 = 0b001)
if !IsFeatureImplemented(FEAT_AA64) then UNDEFINED; elsif PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() == '011' then AArch64.SystemAccessTrap(EL2, 0x18); elsif EffectiveHCR_EL2_NVx() IN {'111'} then X[t, 64] = NVMem[0x230]; else X[t, 64] = ELR_EL1; elsif PSTATE.EL == EL2 then if ELIsInHost(EL2) then X[t, 64] = ELR_EL2; else X[t, 64] = ELR_EL1; elsif PSTATE.EL == EL3 then X[t, 64] = ELR_EL1;
MSR ELR_EL1, <Xt>
(op0 = 0b11, op1 = 0b000, CRn = 0b0100, CRm = 0b0000, op2 = 0b001)
if !IsFeatureImplemented(FEAT_AA64) then UNDEFINED; elsif PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if IsFeatureImplemented(FEAT_GCS) && GetCurrentEXLOCKEN() && !Halted() && PSTATE.EXLOCK == '1' && !(EffectiveHCR_EL2_NVx() IN {'x11'}) then EXLOCKException(); elsif EffectiveHCR_EL2_NVx() == '011' then AArch64.SystemAccessTrap(EL2, 0x18); elsif EffectiveHCR_EL2_NVx() IN {'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' && ELIsInHost(EL2) then EXLOCKException(); elsif ELIsInHost(EL2) then ELR_EL2 = X[t, 64]; else ELR_EL1 = X[t, 64]; elsif PSTATE.EL == EL3 then ELR_EL1 = X[t, 64];
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