PACIB, PACIB1716, PACIBSP, PACIBZ, PACIZB

Pointer Authentication Code for instruction address, using key B

This instruction computes and inserts a Pointer Authentication Code for an instruction address, using a modifier and key B.

The address is:

In the general-purpose register that is specified by <Xd> for PACIB and PACIZB.

In X17, for PACIB1716.

In X30, for PACIBSP and PACIBZ.

The modifier is:

In the general-purpose register or stack pointer that is specified by <Xn|SP> for PACIB.

The value zero, for PACIZB and PACIBZ.

In X16, for PACIB1716.

In SP, for PACIBSP.

If FEAT_PAuth_LR is implemented and PSTATE.PACM is 1, then PACIB1716 and PACIBSP include a second modifier that is:

In X15, for PACIB1716.

The value of PC, for PACIBSP.

A PACIBSP instruction has an implicit BTI instruction. The implicit BTI instruction of a PACIBSP instruction is always compatible with PSTATE.BTYPE == 0b01 and PSTATE.BTYPE == 0b10. Controls in SCTLR_ELx configure whether the implicit BTI instruction of a PACIBSP instruction is compatible with PSTATE.BTYPE == 0b11. For more information, see PSTATE.BTYPE.

Encoding: Integer

Variants: FEAT_PAuth (ARMv8.3)

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	1	0	1	0	1	1	0	0	0	0	0	1	0	0		0	0	1
sf		S									opcode2							Z				Rn					Rd

PACIB (Z == 0)

PACIB <Xd>, <Xn|SP>

PACIZB (Z == 1 && Rn == 11111)

PACIZB <Xd>

Decoding algorithm

if !IsFeatureImplemented(FEAT_PAuth) then EndOfDecode(Decode_UNDEF);
boolean source_is_sp = FALSE;
constant boolean pacib1716 = FALSE;
constant integer d = UInt(Rd);
constant integer n = UInt(Rn);

if Z == '0' then // PACIB
    if n == 31 then source_is_sp = TRUE;
else // PACIZB
    if n != 31 then EndOfDecode(Decode_UNDEF);

Encoding: System

Variants: FEAT_PAuth (ARMv8.3)

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	0	1	0	0	0	0	0	0	1	1	0	0	1	0	0	0	x	1	0	1	x	1	1	1	1	1
																				CRm				op2

PACIB1716 (CRm == 0001 && op2 == 010)

PACIB1716

PACIBSP (CRm == 0011 && op2 == 011)

PACIBSP

PACIBZ (CRm == 0011 && op2 == 010)

PACIBZ

Decoding algorithm

if !IsFeatureImplemented(FEAT_PAuth) then EndOfDecode(Decode_NOP);
integer d;
integer n;
boolean source_is_sp = FALSE;
boolean pacib1716 = FALSE;

case CRm:op2 of
    when '0011 010' // PACIBZ
        d = 30;
        n = 31;
    when '0011 011' // PACIBSP
        d = 30;
        source_is_sp = TRUE;
        if IsFeatureImplemented(FEAT_BTI) then
            // Check for branch target compatibility between PSTATE.BTYPE
            // and implicit branch target of PACIBSP instruction.
            SetBTypeCompatible(BTypeCompatible_PACIXSP());
    when '0001 010' // PACIB1716
        d = 17;
        n = 16;
        pacib1716 = TRUE;

Operation

if source_is_sp then
    if IsFeatureImplemented(FEAT_PAuth_LR) && PSTATE.PACM == '1' then
        X[d, 64] = AddPACIB2(X[d, 64], SP[64], PC64);
    else
        X[d, 64] = AddPACIB(X[d, 64], SP[64]);
else
    if IsFeatureImplemented(FEAT_PAuth_LR) && PSTATE.PACM == '1' && pacib1716 then
        X[d, 64] = AddPACIB2(X[d, 64], X[n, 64], X[15, 64]);
    else
        X[d, 64] = AddPACIB(X[d, 64], X[n, 64]);

Explanations

<Xd>: Is the 64-bit name of the general-purpose destination register, encoded in the "Rd" field.
<Xn|SP>: Is the 64-bit name of the general-purpose source register or stack pointer, encoded in the "Rn" field.