Load-acquire register byte
This instruction derives an address from a base register value, loads a byte from memory, zero-extends it and writes it to a register.
If the destination register is not one of WZR or XZR, LDARB loads from memory with Acquire semantics.
For more information about memory ordering semantics, see Load-Acquire, Load-AcquirePC, and Store-Release.
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 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | (1) | (1) | (1) | (1) | (1) | 1 | (1) | (1) | (1) | (1) | (1) | Rn | Rt | ||||||||
| size | L | Rs | o0 | Rt2 | |||||||||||||||||||||||||||
constant integer t = UInt(Rt); constant integer n = UInt(Rn); constant boolean acquire = t != 31; constant boolean tagchecked = n != 31;
| <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. |
bits(64) address; constant AccessDescriptor accdesc = CreateAccDescAcqRel(MemOp_LOAD, tagchecked, acquire, t); if n == 31 then CheckSPAlignment(); address = SP[64]; else address = X[n, 64]; constant bits(8) data = Mem[address, 1, accdesc]; X[t, 32] = ZeroExtend(data, 32);
This instruction is a data-independent-time instruction as described in About PSTATE.DIT.
Version 2025.09 — Copyright © 2010-2025 Arm Limited or its affiliates.
This site is provided as a community resource and is NOT affiliated with nor endorsed by Arm Limited.