autib

Authenticate Code (Inst B)

AUTIB <Xd>, <Xn|SP>

Authenticates a pointer signed with Key B.

Details

Authenticates a 64-bit pointer in Xd using Key B and a modifier from Xn or SP. If authentication fails, the pointer is corrupted with a known bit pattern. This instruction is AArch64-only and requires the PAC (Pointer Authentication Code) extension. It does not affect the condition flags (N, Z, C, V) but may generate an exception if executed in an inappropriate context.

Pseudocode Operation

authenticated_pointer ← AuthenticatePointer(Xd, Xn, KeyB)
if authentication_fails then
  Xd ← corrupted_value
else
  Xd ← authenticated_pointer
end if

Example

AUTIB x0, x1

Encoding

Binary Layout

11010110

00001

101

Format Data Processing

Opcode 0xDAC11400

Extension PAC (Security)

Operands

Xd
Ptr
Xn
Modifier

Reference (Arm A64 ISA)

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0xDAC11400	AUTIB <Xd>, <Xn\|SP>		A64		1 \| 1 \| 0 \| 11010110 \| 00001 \| 00 \| 0 \| 101 \| Rn \| Rd

Description

Authenticate Instruction address, using key B. This instruction authenticates an instruction address, using a modifier and key B. If the authentication passes, the upper bits of the address are restored to enable subsequent use of the address. For information on behavior if the authentication fails, see Faulting on pointer authentication. The address is: The modifier is: If FEAT_PAuth_LR is implemented and PSTATE.PACM is 1, then AUTIB1716 and AUTIBSP include a second modifier that is:

Operation

if IsFeatureImplemented(FEAT_PAuth) then
    if source_is_sp then
        if IsFeatureImplemented(FEAT_PAuth_LR) && PSTATE.PACM == '1' then
            X[d, 64] = AuthIB2(X[d, 64], SP[], X[16, 64], FALSE);
        else
            X[d, 64] = AuthIB(X[d, 64], SP[], FALSE);
    else
        if IsFeatureImplemented(FEAT_PAuth_LR) && PSTATE.PACM == '1' && autib1716 then
            X[d, 64] = AuthIB2(X[d, 64], X[n, 64], X[15, 64], FALSE);
        else
            X[d, 64] = AuthIB(X[d, 64], X[n, 64], FALSE);