LDAR

Load-acquire register

This instruction derives an address from a base register value, loads a 32-bit word or 64-bit doubleword from memory, and writes it to a register.

If the destination register is not one of WZR or XZR, LDAR 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
1	x	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

32-bit encoding

(size == 10)

LDAR <Wt>, [<Xn|SP>{, #0}]

64-bit encoding

(size == 11)

LDAR <Xt>, [<Xn|SP>{, #0}]

Decode (all encodings)

constant integer t = UInt(Rt); constant integer n = UInt(Rn); constant integer elsize = 8 << UInt(size); constant integer regsize = if elsize == 64 then 64 else 32; constant boolean acquire = t != 31; constant boolean tagchecked = n != 31;

Assembler Symbols

<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.

<Xt>	Is the 64-bit name of the general-purpose register to be transferred, encoded in the "Rt" field.

Operation

bits(64) address; constant integer dbytes = elsize DIV 8; constant AccessDescriptor accdesc = CreateAccDescAcqRel(MemOp_LOAD, tagchecked, acquire, t); if n == 31 then CheckSPAlignment(); address = SP[64]; else address = X[n, 64]; constant bits(elsize) data = Mem[address, dbytes, accdesc]; X[t, regsize] = ZeroExtend(data, regsize);

Operational information

This instruction is a data-independent-time instruction as described in About PSTATE.DIT.

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