autia

Authenticate Code (Inst A)

AUTIA <Xd>, <Xn|SP>

Authenticates a pointer signed with Key A. Corrupts pointer if failed.

Details

Authenticates a 64-bit pointer in Xd using Key A 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, KeyA)
if authentication_fails then
  Xd ← corrupted_value
else
  Xd ← authenticated_pointer
end if

Example

AUTIA x0, x1

Encoding

Binary Layout
1
1
0
11010110
00001
00
0
100
Rn
Rd
 
Format Data Processing
Opcode 0xDAC11000
Extension PAC (Security)

Operands

  • Xd
    Ptr
  • Xn
    Modifier

Reference (Arm A64 ISA)

Instruction Forms

Encoding Instruction ISA Bit pattern
0xDAC11000 AUTIA <Xd>, <Xn|SP> A64 1 | 1 | 0 | 11010110 | 00001 | 00 | 0 | 100 | Rn | Rd

Description

Authenticate Instruction address, using key A. This instruction authenticates an instruction address, using a modifier and key A. 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 AUTIA1716 and AUTIASP 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] = AuthIA2(X[d, 64], SP[], X[16, 64], FALSE);
        else
            X[d, 64] = AuthIA(X[d, 64], SP[], FALSE);
    else
        if IsFeatureImplemented(FEAT_PAuth_LR) && PSTATE.PACM == '1' && autia1716 then
            X[d, 64] = AuthIA2(X[d, 64], X[n, 64], X[15, 64], FALSE);
        else
            X[d, 64] = AuthIA(X[d, 64], X[n, 64], FALSE);