Index

RETAA, RETAB

Return from subroutine, with pointer authentication. This instruction authenticates the address that is held in LR, using SP as the modifier and the specified key, and branches to the authenticated address, with a hint that this instruction is a subroutine return.

Key A is used for RETAA. Key B is used for RETAB.

If the authentication passes, the PE continues execution at the target of the branch. For information on behavior if the authentication fails, see Faulting on pointer authentication.

The authenticated address is not written back to LR.

If FEAT_PAuth_LR is implemented and PSTATE.PACM is 1, then RETAA and RETAB include a second modifier that is in X16.

Integer
(FEAT_PAuth)

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
1 1 0 1 0 1 1 0 0 1 0 1 1 1 1 1 0 0 0 0 1 M 1 1 1 1 1 1 1 1 1 1
Z op A Rn Rm

RETAA (M == 0)

RETAA

RETAB (M == 1)

RETAB

boolean use_key_a = (M == '0');

if !IsFeatureImplemented(FEAT_PAuth) then
    UNDEFINED;

Operation

GCSInstruction inst_type;
bits(64) target = X[30, 64];

bits(64) modifier = SP[];
bits(64) modifier2;
boolean use_modifier2 = FALSE;
if (IsFeatureImplemented(FEAT_PAuth_LR) && PSTATE.PACM == '1') then
    modifier2 = X[16, 64];
    use_modifier2 = TRUE;

if use_key_a then
    if use_modifier2 && IsFeatureImplemented(FEAT_PAuth_LR) then
        target = AuthIA2(target, modifier, modifier2, TRUE);
    else
        target = AuthIA(target, modifier, TRUE);
else
    if use_modifier2 && IsFeatureImplemented(FEAT_PAuth_LR) then
        target = AuthIB2(target, modifier, modifier2, TRUE);
    else
        target = AuthIB(target, modifier, TRUE);

if (IsFeatureImplemented(FEAT_GCS) && GCSPCREnabled(PSTATE.EL)) then
    inst_type = if use_key_a then GCSInstType_PRETAA else GCSInstType_PRETAB;
    target = LoadCheckGCSRecord(target, inst_type);
    SetCurrentGCSPointer(GetCurrentGCSPointer() + 8);

// Value in BTypeNext will be used to set PSTATE.BTYPE
BTypeNext = '00';

BranchTo(target, BranchType_RET, FALSE);