assembly - Xtensa 指令：L32R - 加载了哪些地址？

Question

我正在尝试阅读一些 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

这个加载哪个地址？

Answer 1

Xtensa 指令集架构参考手册手册第 382 页上的说明，地址l32r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.

所以在继续上面的例子中；常量的操作：

     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

Answer 2

L32R 指令从指定地址加载一个 32 位值。因此“l32r a2, 2ec8”将位于地址 0x2ec8 的 32 位值加载到寄存器 a2 中。您必须在反汇编中查看该位置。