Index

BRAA, BRAAZ, BRAB, BRABZ

Branch to Register, with pointer authentication. This instruction authenticates the address in the general-purpose register that is specified by <Xn>, using a modifier and the specified key, and branches to the authenticated address.

The modifier is:

Key A is used for BRAA and BRAAZ. Key B is used for BRAB and BRABZ.

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 the general-purpose register.

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

Key A, zero modifier (Z == 0 && M == 0 && Rm == 11111)

BRAAZ <Xn>

Key A, register modifier (Z == 1 && M == 0)

BRAA <Xn>, <Xm|SP>

Key B, zero modifier (Z == 0 && M == 1 && Rm == 11111)

BRABZ <Xn>

Key B, register modifier (Z == 1 && M == 1)

BRAB <Xn>, <Xm|SP>

integer n = UInt(Rn);
integer m = UInt(Rm);
boolean use_key_a = (M == '0');
boolean source_is_sp = ((Z == '1') && (m == 31));

if !IsFeatureImplemented(FEAT_PAuth) then
    UNDEFINED;

if Z == '0' && m != 31 then
    UNDEFINED;

Assembler Symbols

<Xn>

Is the 64-bit name of the general-purpose register holding the address to be branched to, encoded in the "Rn" field.
<Xm|SP>

Is the 64-bit name of the general-purpose source register or stack pointer holding the modifier, encoded in the "Rm" field.

Operation

bits(64) target = X[n, 64];

bits(64) modifier = if source_is_sp then SP[] else X[m, 64];
if use_key_a then
    target = AuthIA(target, modifier, TRUE);
else
    target = AuthIB(target, modifier, TRUE);

// Value in BTypeNext will be used to set PSTATE.BTYPE
if InGuardedPage then
    if n == 16 || n == 17 then
        BTypeNext = '01';
    else
        BTypeNext = '11';
else
    BTypeNext = '01';
BranchTo(target, BranchType_INDIR, FALSE);