ldapr

Load-Acquire RCpc Register

LDAPR <Wt>, [<Xn|SP>]

Loads a word with RCpc Acquire semantics.

Pseudocode Operation

Wt ← [Xn]; // Load with RCpc acquire semantics; address alignment: 4 bytes

Example

LDAPR w3, [x1]

Encoding

Binary Layout

10

31:30

111

29:27

0

26

00

25:24

1

23

0

22

1

21

11111

20:16

1

15

100

14:12

00

11:10

Rn

9:5

Rt

4:0

 

Format Load/Store

Opcode 0xB8BFC000

Extension Base (RCpc)

Operands

• Wt
  Transfer 32-bit integer register (load/store)
• Xn
  First source / base 64-bit integer register

Related

More in Base (RCpc)

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x99C00800	LDAPR <Wt>, [<Xn|SP>], #4		A64		10 | 0110011 | 1 | 000000000010 | Rn | Rt
0xD9C00800	LDAPR <Xt>, [<Xn|SP>], #8		A64		11 | 0110011 | 1 | 000000000010 | Rn | Rt
0xB8BFC000	LDAPR <Wt>, [<Xn|SP> {, #0}]		A64		10 | 111 | 0 | 00 | 1 | 0 | 1 | 11111 | 1 | 100 | 00 | Rn | Rt
0xF8BFC000	LDAPR <Xt>, [<Xn|SP> {, #0}]		A64		11 | 111 | 0 | 00 | 1 | 0 | 1 | 11111 | 1 | 100 | 00 | Rn | Rt

Description

Load-Acquire RCpc Register 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. The instruction has memory ordering semantics as described in Load-Acquire, Load-AcquirePC, and Store-Release, except that: This difference in memory ordering is not described in the pseudocode. For information about memory accesses, see Load/Store addressing modes.

Operation

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

AccessDescriptor accdesc = CreateAccDescLDAcqPC(tagchecked);

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

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

if wback then
    if wb_unknown then
        address = bits(64) UNKNOWN;
    else
        address = GenerateAddress(address, offset, accdesc);
    if n == 31 then
        SP[] = address;
    else
        X[n, 64] = address;