STRB (immediate)
Store register byte (immediate)
This instruction stores the least significant byte of a 32-bit register
to memory. The address that is used for the store is calculated from a base register
and an immediate offset. For information about addressing modes, see
Load/Store addressing modes.
For information about the CONSTRAINED UNPREDICTABLE behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors, and particularly STRB (immediate).
This instruction is a data-independent-time instruction as described in About PSTATE.DIT.
It has encodings from 3 classes:
Post-index
,
Pre-index
and
Unsigned offset
0
0
1
1
1
0
0
0
0
0
0
0
1
STRB <Wt>, [<Xn|SP>], #<simm>
let wback : boolean = TRUE;
let postindex : boolean = TRUE;
let offset : bits(64) = SignExtend{}(imm9);
0
0
1
1
1
0
0
0
0
0
0
1
1
STRB <Wt>, [<Xn|SP>, #<simm>]!
let wback : boolean = TRUE;
let postindex : boolean = FALSE;
let offset : bits(64) = SignExtend{}(imm9);
0
0
1
1
1
0
0
1
0
0
STRB <Wt>, [<Xn|SP>{, #<pimm>}]
let wback : boolean = FALSE;
let postindex : boolean = FALSE;
let offset : bits(64) = LSL(ZeroExtend{64}(imm12), 0);
<Wt>
Is the 32-bit name of the general-purpose register to be transferred, encoded in the "Rt" field.
<Xn|SP>
Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field.
<simm>
Is the signed immediate byte offset, in the range -256 to 255, encoded in the "imm9" field.
<pimm>
Is the optional positive immediate byte offset, in the range 0 to 4095, defaulting to 0 and encoded in the "imm12" field.
let t : integer{} = UInt(Rt);
let n : integer{} = UInt(Rn);
let nontemporal : boolean = FALSE;
let tagchecked : boolean = wback || n != 31;
var c : Constraint;
var rt_unknown : boolean = FALSE;
if wback && n == t && n != 31 then
c = ConstrainUnpredictable(Unpredictable_WBOVERLAPST);
assert c IN {Constraint_NONE, Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP};
case c of
when Constraint_NONE => rt_unknown = FALSE; // Value stored is original value
when Constraint_UNKNOWN => rt_unknown = TRUE; // Value stored is UNKNOWN
when Constraint_UNDEF => EndOfDecode(Decode_UNDEF);
when Constraint_NOP => EndOfDecode(Decode_NOP);
end;
end;
var address : bits(64);
let privileged : boolean = PSTATE.EL != EL0;
let accdesc : AccessDescriptor = CreateAccDescGPR(MemOp_STORE, nontemporal, privileged,
tagchecked, t);
if n == 31 then
CheckSPAlignment();
address = SP{64}();
else
address = X{64}(n);
end;
if !postindex then
address = AddressAdd(address, offset, accdesc);
end;
var data : bits(8);
if rt_unknown then
data = ARBITRARY : bits(8);
else
data = X{8}(t);
end;
Mem{8}(address, accdesc) = data;
if wback then
if postindex then
address = AddressAdd(address, offset, accdesc);
end;
if n == 31 then
SP{64}() = address;
else
X{64}(n) = address;
end;
end;
2026-03-26 20:27:25
2026-03_rel