Page 83 - ARM 64 Bit Assembly Language

68 Chapter 3

1 ldursb x4, [x5, #255]
Store the double-word value in x1 to Mem[x2 - 256]:

1 stur x1, [x2, #-256]

3.4.3 Load/store pair

These instructions are used to store or load two registers at a time. This can be useful for mov-
ing registers onto the stack or for copying data. These two instructions are particularly useful
for transferring data in a load-store architecture because each instruction can move twice as
much information as the ldr and str instructions.

ldp Load Pair, and
stp Store Pair.

3.4.3.1 Syntax

<op>{<size>} Rt, Rt2, <addr>

• <op> is either ldp or stp.
• <size> is optionally sw for signed words.
• <addr> is 7 bits Pre-indexed, Post-indexed, or Signed immediate.
• Signed immediate Xt range: [-0x200, 0x1f8]. Wt range: [-0x100, 0xfc].

3.4.3.2 Operations

Name Effect Description
ldp Rt ← Mem[addr] Load register pair from memory at
Rt2 ← Mem[addr+size(Rt)] addr where sizeof(Rt) is 4 for Wt
registers and 8 for Xt registers
stp Mem[addr] ← Rt Store register pair in memory at addr
Mem[addr+size(Rt)] ← Rt2

3.4.3.3 Examples

The stp and ldp instructions are commonly used at the beginning of a function, and at the
end of a function. For example, the following instruction allocates sixteen bytes on the stack
by decrementing the stack pointer. Then it stores the frame pointer (x29)at Mem[sp] (the