LDRB (register)

Load register byte (register)

This instruction calculates an address from a base register value and an offset register value, loads a byte from memory, zero-extends it, and writes it to a register. For information about addressing modes, see Load/Store addressing modes.

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

Extended register encoding

(option != 011)

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

Shifted register encoding

(option == 011)

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

Decode (all encodings)

if option<1> == '0' then EndOfDecode(Decode_UNDEF); // sub-word index constant ExtendType extend_type = DecodeRegExtend(option); constant integer shift = 0;

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.

Is the index extend specifier, encoded in option:

option	<extend>
010	UXTW
110	SXTW
111	SXTX

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

Shared Decode

constant integer t = UInt(Rt); constant integer n = UInt(Rn); constant integer m = UInt(Rm); constant boolean nontemporal = FALSE; constant boolean tagchecked = TRUE;

Operation

constant bits(64) offset = ExtendReg(m, extend_type, shift, 64); bits(64) address; constant boolean privileged = PSTATE.EL != EL0; constant AccessDescriptor accdesc = CreateAccDescGPR(MemOp_LOAD, nontemporal, privileged, tagchecked, t); if n == 31 then CheckSPAlignment(); address = SP[64]; else address = X[n, 64]; address = AddressAdd(address, offset, accdesc); constant bits(8) data = Mem[address, 1, accdesc]; X[t, 32] = ZeroExtend(data, 32);

Operational information

This instruction is a data-independent-time instruction as described in About PSTATE.DIT.

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