Load Register Signed Halfword (unprivileged) loads a halfword from memory, sign-extends it to 32 bits or 64 bits, and writes the result to a register. The address that is used for the load is calculated from a base register and an immediate offset.
Memory accesses made by the instruction behave as if the instruction was executed at EL0 if the Effective value of PSTATE.UAO is 0 and either:
Otherwise, the memory access operates with the restrictions determined by the Exception level at which the instruction is executed. For information about memory accesses, 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 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | x | 0 | imm9 | 1 | 0 | Rn | Rt | ||||||||||||||||
| size | VR | opc | |||||||||||||||||||||||||||||
bits(64) offset = SignExtend(imm9, 64);
| <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. |
integer n = UInt(Rn); integer t = UInt(Rt); MemOp memop; boolean signed; integer regsize; if opc<1> == '0' then // store or zero-extending load memop = if opc<0> == '1' then MemOp_LOAD else MemOp_STORE; regsize = 32; signed = FALSE; else // sign-extending load memop = MemOp_LOAD; regsize = if opc<0> == '1' then 32 else 64; signed = TRUE; boolean tagchecked = memop != MemOp_PREFETCH && (n != 31);
bits(64) address; bits(16) data; boolean privileged = AArch64.IsUnprivAccessPriv(); AccessDescriptor accdesc = CreateAccDescGPR(memop, FALSE, privileged, tagchecked); if n == 31 then if memop != MemOp_PREFETCH then CheckSPAlignment(); address = SP[]; else address = X[n, 64]; address = GenerateAddress(address, offset, accdesc); case memop of when MemOp_STORE data = X[t, 16]; Mem[address, 2, accdesc] = data; when MemOp_LOAD data = Mem[address, 2, accdesc]; if signed then X[t, regsize] = SignExtend(data, regsize); else X[t, regsize] = ZeroExtend(data, regsize); when MemOp_PREFETCH Prefetch(address, t<4:0>);
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: aarchmrs v2023-12_rel, pseudocode v2023-12_rel, sve v2023-12_rel ; Build timestamp: 2023-12-15T16:46
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