LDAR

Load-Acquire Register 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. The instruction also has memory ordering semantics as described in Load-Acquire, Store-Release. For information about memory accesses, see Load/Store addressing modes.

Note

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
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 (size == 10)

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

64-bit (size == 11)

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

integer n = UInt(Rn);
integer t = UInt(Rt);

constant integer elsize = 8 << UInt(size);
constant integer regsize = if elsize == 64 then 64 else 32;
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.

<Xt>	Is the 64-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.

Operation

bits(64) address;
bits(elsize) data;
constant integer dbytes = elsize DIV 8;

AccessDescriptor accdesc;
accdesc = CreateAccDescAcqRel(MemOp_LOAD, tagchecked);

if n == 31 then
    CheckSPAlignment();
    address = SP[];
else
    address = X[n, 64];

data = Mem[address, dbytes, accdesc];
X[t, regsize] = ZeroExtend(data, regsize);

Operational information

If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored.