assembly - Xtensa指令: L32R - which addres is loaded?

Question

我正在尝试读取一些 xtensa 汇编代码，但被 L32R 指令难住了:

例如给定以下行:

0000 2f04 <my_func>:
     2f0c:  ffef21          l32r    a2, 2ec8

加载哪个地址？

Answer 1

Xtensa Instruction Set Architecture Reference Manual手册第 382 页指出，对于 l32r，地址计算如下:

L32R forms a virtual address by adding the 16-bit one-extended constant value encoded
in the instruction word shifted left by two to the address of the L32R plus three with the
two least significant bits cleared. Therefore, the offset can always specify 32-bit aligned
addresses from -262141 to -4 bytes from the address of the L32R instruction. 32 bits
(four bytes) are read from the physical address.

所以继续上面的例子；常数的处理:

     ffef    16-bit constant
ffff ffef    16-bit constant one-extended
ffff ffbc    shifted left by two

电脑操作:

0000 2f0c    program counter
0000 2f0f    pc +3
0000 0f0c    masked bits 0 and 1

虚拟地址的计算:

  ffff ffbc
+ 0000 2f0c
===========
1 0000 2ec8

因此丢弃 16 位以外的所有内容:2ec8