问题描述
ARM 汇编中的这一行是做什么的?
What does this line in ARM assembly do?
mrc p15, 0, %0, c9, c13, 0" : : "r" (counter)
什么是p15?通常寄存器以 r 为前缀，例如 r15.
What is p15? Usually registers are prefixed with r such as in r15.
:: 的符号是什么，作用是什么或c9,c1?
What is the symbol :: and what are the roles or c9, c1?
推荐答案
虽然 MRC 是通用协处理器互操作指令，cp15 是 控制处理器 - 所有现代 ARM CPU 都有，ARM 已经使用它来扩展片上单元的指令集，例如缓存、MMU、性能监控等.
Whilst MRC is a generic co-processor inter-op instruction, cp15 is the control processor - which all modern ARM CPUs have and this has been used by ARM was a means of extending the instruction set for on-chip units such as the cache, MMU, performance monitoring and lots else besides.
一次接受你的指示:
mrc p15, 0, %0, c9, c13, 0" : : "r" (计数器)
根据 ARM Cortex A7 MPCore 参考 指令格式为:
MRC{cond} P15、、、、、
在第 4-11 页，这被描述为将 CPU 寄存器传输到性能监视器计数寄存器(我猜 count=0，这是性能计数器的重置).
And on Page 4-11 this is described as a transfer of a CPU register to the performance monitor count register (I guess count=0 and this is a reset of the performance counter).
至于内联汇编器的语法.有关 x86 概述，请参阅此- 这可能类似于 ARM.
As for the syntax of inline assembler. refer to this for a x86 overview - which is probably similar to ARM.
: : "r" (counter) 表示指令有:
- 需要以局部变量结尾的寄存器中没有输出
- 从变量
counter中获取输入，它所在的寄存器应该用作%0. - 没有编译器应该注意的副作用(clobbers)
- No output in a register that needs to end up in a local variable
- Takes input from variable
counter, and the register this is in should be used as%0. - There are no side effects the compiler ought to be aware of (clobbers)
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