Load-acquire RCpc register
This instruction derives an address from a base register value, loads a 32-bit word or 64-bit doubleword from the derived address in memory, and writes it to a register.
If the destination register is not one of WZR or XZR, LDAPR loads from memory with AcquirePC 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.
It has encodings from 2 classes: Post-index and No offset
| 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 |
| 1 | x | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | Rn | Rt | ||||||||
| size | L | ||||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_LRCPC3) then EndOfDecode(Decode_UNDEF); end; let t : integer{} = UInt(Rt); let n : integer{} = UInt(Rn); var wback : boolean = TRUE; let acquirepc : boolean = TRUE; let regsize : integer{} = if size == '11' then 64 else 32; let datasize : integer{} = 8 << UInt(size); let offset : integer = 1 << UInt(size); let tagchecked : boolean = TRUE; var wb_unknown : boolean = FALSE; if n == t && n != 31 then let c : Constraint = 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 => EndOfDecode(Decode_UNDEF); when Constraint_NOP => EndOfDecode(Decode_NOP); end; end;
| 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 |
| 1 | x | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 0 | 1 | (1) | (1) | (1) | (1) | (1) | 1 | 1 | 0 | 0 | 0 | 0 | Rn | Rt | ||||||||
| size | VR | A | R | Rs | o3 | opc | |||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_LRCPC) then EndOfDecode(Decode_UNDEF); end; let t : integer{} = UInt(Rt); let n : integer{} = UInt(Rn); let wback : boolean = FALSE; let offset : integer = 0; let wb_unknown : boolean = FALSE; let elsize : integer{} = 8 << UInt(size); let regsize : integer{} = if elsize == 64 then 64 else 32; let datasize : integer{} = elsize; let acquirepc : boolean = TRUE; let tagchecked : boolean = n != 31;
| <Wt> |
Is the 32-bit name of the general-purpose register to be loaded, 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. |
| <Xt> |
Is the 64-bit name of the general-purpose register to be loaded, encoded in the "Rt" field. |
var address : bits(64); var data : bits(datasize); let dbytes : integer{} = datasize DIV 8; let accdesc : AccessDescriptor = CreateAccDescLDAcqPC(tagchecked, acquirepc, t); if n == 31 then CheckSPAlignment(); address = SP{64}(); else address = X{64}(n); end; data = Mem{datasize}(address, accdesc); X{regsize}(t) = ZeroExtend{regsize}(data); if wback then if wb_unknown then address = ARBITRARY : bits(64); else address = AddressAdd(address, offset, accdesc); end; if n == 31 then SP{64}() = address; else X{64}(n) = address; end; end;
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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