st2g

Store Allocation Tag (Two Granules)

ST2G <Xt|SP>, [<Xn|SP>, #<simm>]

Stores the Allocation Tag to two memory granules.

Pseudocode Operation

address ← Xn + (SignExtend(imm9, 9) << 4)
tag ← GetAllocationTag(Xt)
memory[address] ← memory[address] with tag set to tag
memory[address + 16] ← memory[address + 16] with tag set to tag

Example

ST2G Xt, [x1, #-8]

Encoding

Binary Layout

11011001

31:24

10

23:22

1

21

imm9

20:12

10

11:10

Xn

9:5

Xt

4:0

 

Format Load/Store

Opcode 0xD9A00800

Extension MTE (Memory Tagging)

Operands

• Xt
  Source Tag
• Xn
  First source / base 64-bit integer register
• simm
  Signed immediate offset

Related

More in MTE (Memory Tagging)

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0xD9A00400	ST2G <Xt|SP>, [<Xn|SP>], #<simm>		A64		11011001 | 10 | 1 | imm9 | 01 | Xn | Xt
0xD9A00C00	ST2G <Xt|SP>, [<Xn|SP>, #<simm>]!		A64		11011001 | 10 | 1 | imm9 | 11 | Xn | Xt
0xD9A00800	ST2G <Xt|SP>, [<Xn|SP>{, #<simm>}]		A64		11011001 | 10 | 1 | imm9 | 10 | Xn | Xt

Description

Store Allocation Tags stores an Allocation Tag to two Tag granules of memory. 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.

Operation

bits(64) address;
bits(64) address2;
bits(64) data = if t == 31 then SP[] else X[t, 64];
bits(4) tag = AArch64.AllocationTagFromAddress(data);

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

AccessDescriptor accdesc = CreateAccDescLDGSTG(MemOp_STORE, FALSE);

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

address2 = GenerateAddress(address, TAG_GRANULE, accdesc);

AArch64.MemTag[address, accdesc] = tag;
AArch64.MemTag[address2, accdesc] = tag;

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

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