LDURSB -- A64

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LDURSB -- A64

LDURSB

Load register signed byte (unscaled)

This instruction calculates an address from a base register and an immediate offset, loads a signed byte from memory, sign-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	1	x	0	imm9									0	0	Rn					Rt
size					VR			opc

Encoding for the 32-bit variant

Applies when (opc == 11)

LDURSB <Wt>, [<Xn|SP>{, #<simm>}]

Encoding for the 64-bit variant

Applies when (opc == 10)

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

Decode for all variants of this encoding

let offset : bits(64) = SignExtend{}(imm9);

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.

<simm>

Is the optional signed immediate byte offset, in the range -256 to 255, defaulting to 0 and encoded in the "imm9" field.

<Xt>	Is the 64-bit name of the general-purpose register to be transferred, encoded in the "Rt" field.

Shared Decode

let n : integer = UInt(Rn); let t : integer = UInt(Rt); let datasize : integer{} = 8; let regsize : integer{} = 64 >> UInt(opc[0]); let nontemporal : boolean = FALSE; let tagchecked : boolean = n != 31;

Operation

var address : bits(64); let privileged : boolean = PSTATE.EL != EL0; let accdesc : AccessDescriptor = CreateAccDescGPR(MemOp_LOAD, nontemporal, privileged, tagchecked, t); if n == 31 then CheckSPAlignment(); address = SP{64}(); else address = X{64}(n); end; address = AddressAdd(address, offset, accdesc); let data : bits(datasize) = Mem{datasize}(address, accdesc); X{regsize}(t) = SignExtend{regsize}(data);

Operational information

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

2026-03_rel 2026-03-26 20:48:11

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