Load-Acquire Register Byte derives an address from a base register value, loads a byte from memory, zero-extends it and writes it to a register. The instruction also has memory ordering semantics as described in Load-Acquire, Store-Release. For information about memory accesses, see Load/Store addressing modes.
For this instruction, if the destination is WZR/XZR, it is impossible for software to observe the presence of the acquire semantic other than its effect on the arrival at endpoints.
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 |
integer n = UInt(Rn); integer t = UInt(Rt); integer t2 = UInt(Rt2); // ignored by load/store single register integer s = UInt(Rs); // ignored by all loads and store-release AccType acctype = if o0 == '0' then AccType_LIMITEDORDERED else AccType_ORDERED; MemOp memop = if L == '1' then MemOp_LOAD else MemOp_STORE; integer elsize = 8 << UInt(size); integer regsize = if elsize == 64 then 64 else 32; integer datasize = elsize; boolean tag_checked = 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; bits(datasize) data; constant integer dbytes = datasize DIV 8; if HaveMTE2Ext() then SetTagCheckedInstruction(tag_checked); if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n]; case memop of when MemOp_STORE data = X[t]; Mem[address, dbytes, acctype] = data; when MemOp_LOAD data = Mem[address, dbytes, acctype]; X[t] = ZeroExtend(data, regsize);
If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored.
Internal version only: isa v33.11seprel, AdvSIMD v29.05, pseudocode v2021-09_rel, sve v2021-09_rc3d ; Build timestamp: 2021-10-06T11:41
Copyright © 2010-2021 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.