Index

STRB (register)

Store Register Byte (register) calculates an address from a base register value and an offset register value, and stores a byte from a 32-bit register to the calculated address. For information about memory accesses, see Load/Store addressing modes.

The instruction uses an offset addressing mode, that calculates the address used for the memory access from a base register value and an offset register value. The offset can be optionally shifted and extended.

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
0 0 1 1 1 0 0 0 0 0 1 Rm option S 1 0 Rn Rt
size opc

Extended register (option != 011)

STRB <Wt>, [<Xn|SP>, (<Wm>|<Xm>), <extend> {<amount>}]

Shifted register (option == 011)

STRB <Wt>, [<Xn|SP>, <Xm>{, LSL <amount>}]

if option<1> == '0' then UNDEFINED;    // sub-word index
ExtendType extend_type = DecodeRegExtend(option);

Assembler Symbols

<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.
<Wm>

When option<0> is set to 0, is the 32-bit name of the general-purpose index register, encoded in the "Rm" field.
<Xm>

When option<0> is set to 1, is the 64-bit name of the general-purpose index register, encoded in the "Rm" field.
<extend>

Is the index extend specifier, encoded in option:

option <extend>
010 UXTW
110 SXTW
111 SXTX
<amount>

Is the index shift amount, it must be #0, encoded in "S" as 0 if omitted, or as 1 if present.

Shared Decode

integer n = UInt(Rn);
integer t = UInt(Rt);
integer m = UInt(Rm);

Operation

bits(64) offset = ExtendReg(m, extend_type, 0, 64);
bits(64) address;
bits(8) data;

boolean privileged = PSTATE.EL != EL0;
AccessDescriptor accdesc = CreateAccDescGPR(MemOp_STORE, FALSE, privileged, TRUE);

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

address = GenerateAddress(address, offset, accdesc);

data = X[t, 8];
Mem[address, 1, accdesc] = data;

Operational information

If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored.