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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:

  • In the general-purpose register or stack pointer that is specified by <Xm|SP> for BRAA and BRAB.
  • The value zero, for BRAAZ and BRABZ.

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

If the authentication passes, the PE continues execution at the target of the branch. If the authentication fails, a Translation fault is generated.

The authenticated address is not written back to the general-purpose register.

Integer
(Armv8.3)

313029282726252423222120191817161514131211109876543210
1101011Z0001111100001MRnRm
opA

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 !HavePACExt() 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];

bits(64) modifier = if source_is_sp then SP[] else X[m];

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);
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