Load Register Byte (unscaled) calculates an address from a base register and an immediate offset, loads a byte from memory, zero-extends it, and writes it to a register. 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 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | imm9 | 0 | 0 | Rn | Rt | ||||||||||||||||
| size | opc | ||||||||||||||||||||||||||||||
boolean wback = FALSE; boolean postindex = FALSE; integer scale = UInt(size); 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. |
| <Cn|CSP> |
Is the name of the capability register or capability stack pointer holding the base address, 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. |
integer n = UInt(Rn); integer t = UInt(Rt); AccType acctype = AccType_NORMAL; 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 = if size == '11' then 64 else 32; signed = FALSE; else if size == '11' then memop = MemOp_PREFETCH; if opc<0> == '1' then UNDEFINED; else // sign-extending load memop = MemOp_LOAD; if size == '10' && opc<0> == '1' then UNDEFINED; regsize = if opc<0> == '1' then 32 else 64; signed = TRUE; integer datasize = 8 << scale;
bits(64) address; bits(datasize) data; boolean wb_unknown = FALSE; boolean rt_unknown = FALSE; if memop == MemOp_LOAD && wback && n == t && n != 31 then c = ConstrainUnpredictable(Unpredictable_WBOVERLAPLD); assert c IN {Constraint_WBSUPPRESS, Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP}; case c of when Constraint_WBSUPPRESS wback = FALSE; // writeback is suppressed when Constraint_UNKNOWN wb_unknown = TRUE; // writeback is UNKNOWN when Constraint_UNDEF UNDEFINED; when Constraint_NOP EndOfInstruction(); if memop == MemOp_STORE && wback && n == t && n != 31 then c = ConstrainUnpredictable(Unpredictable_WBOVERLAPST); assert c IN {Constraint_NONE, Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP}; case c of when Constraint_NONE rt_unknown = FALSE; // value stored is original value when Constraint_UNKNOWN rt_unknown = TRUE; // value stored is UNKNOWN when Constraint_UNDEF UNDEFINED; when Constraint_NOP EndOfInstruction(); VirtualAddress base; base = BaseReg[n, memop == MemOp_PREFETCH]; address = VAddress(base); if ! postindex then address = address + offset; case memop of when MemOp_STORE VACheckAddress(base, address, datasize DIV 8, CAP_PERM_STORE, acctype); if rt_unknown then data = bits(datasize) UNKNOWN; else data = X[t]; Mem[address, datasize DIV 8, acctype] = data; when MemOp_LOAD VACheckAddress(base, address, datasize DIV 8, CAP_PERM_LOAD, acctype); data = Mem[address, datasize DIV 8, acctype]; if signed then X[t] = SignExtend(data, regsize); else X[t] = ZeroExtend(data, regsize); when MemOp_PREFETCH address = VAddress(base); Prefetch(address, t<4:0>); if wback then if wb_unknown then base = VirtualAddress UNKNOWN; else base = VAAdd(base,offset); BaseReg[n] = base;
Internal version only: isa v32.13, AdvSIMD v29.04, pseudocode morello-2022-01_rc2, capabilities morello-2022-01_rc2 ; Build timestamp: 2022-01-11T11:23
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