Index

STZG

Store Allocation Tag, Zeroing stores an Allocation Tag to memory, zeroing the associated data location. The address used for the store is calculated from the base register and an immediate signed offset scaled by the Tag granule. The Allocation Tag is calculated from the Logical Address Tag in the source register.

This instruction generates an Unchecked access.

It has encodings from 3 classes: Post-index , Pre-index and Signed offset

Post-index
(FEAT_MTE)

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 0 1 0 1 1 imm9 0 1 Xn Xt

STZG <Xt|SP>, [<Xn|SP>], #<simm>

if !IsFeatureImplemented(FEAT_MTE) then UNDEFINED;
integer n = UInt(Xn);
integer t = UInt(Xt);
bits(64) offset = LSL(SignExtend(imm9, 64), LOG2_TAG_GRANULE);
boolean writeback = TRUE;
boolean postindex = TRUE;

Pre-index
(FEAT_MTE)

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 0 1 0 1 1 imm9 1 1 Xn Xt

STZG <Xt|SP>, [<Xn|SP>, #<simm>]!

if !IsFeatureImplemented(FEAT_MTE) then UNDEFINED;
integer n = UInt(Xn);
integer t = UInt(Xt);
bits(64) offset = LSL(SignExtend(imm9, 64), LOG2_TAG_GRANULE);
boolean writeback = TRUE;
boolean postindex = FALSE;

Signed offset
(FEAT_MTE)

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 0 1 0 1 1 imm9 1 0 Xn Xt

STZG <Xt|SP>, [<Xn|SP>{, #<simm>}]

if !IsFeatureImplemented(FEAT_MTE) then UNDEFINED;
integer n = UInt(Xn);
integer t = UInt(Xt);
bits(64) offset = LSL(SignExtend(imm9, 64), LOG2_TAG_GRANULE);
boolean writeback = FALSE;
boolean postindex = FALSE;

Assembler Symbols

<Xt|SP>

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

Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Xn" field.
<simm>

Is the optional signed immediate offset, a multiple of 16 in the range -4096 to 4080, defaulting to 0 and encoded in the "imm9" field.

Operation

bits(64) address;

if n == 31 then
    CheckSPAlignment();
    address = SP[];
else
    address = X[n, 64];

AccessDescriptor accdesc = CreateAccDescLDGSTG(MemOp_STORE);

if !postindex then
    address = GenerateAddress(address, offset, accdesc);

if !IsAligned(address, TAG_GRANULE) then
    AArch64.Abort(address, AlignmentFault(accdesc));

Mem[address, TAG_GRANULE, accdesc] = Zeros(TAG_GRANULE * 8);

bits(64) data = if t == 31 then SP[] else X[t, 64];
bits(4) tag = AArch64.AllocationTagFromAddress(data);
AArch64.MemTag[address, accdesc] = tag;

if writeback then
    if postindex then
        address = GenerateAddress(address, offset, accdesc);

    if n == 31 then
        SP[] = address;
    else
        X[n, 64] = address;