mrc p15在ARM内联汇编中起什么作用，GNU C内联asm语法如何工作? [英] What does mrc p15 do in ARM inline assembly, and how does GNU C inline asm syntax work?

问题描述

装配臂中的这条线有什么作用?

what does this line in assembly arm does?

mrc p15, 0, %0, c9, c13, 0" : : "r" (counter)

谁是p15难道不是r15其他人是什么?

who is p15 isn't it should be r15 what are all the others?

::是什么?c9, c1每个自变量的作用是什么?

what is :: who are c9, c1 what is the role of each argument?

推荐答案

MRC是通用协处理器互操作指令，cp15是控制处理器-所有这些ARM CPU已经被ARM使用，这已被ARM用来扩展诸如高速缓存，MMU，性能监控之类的片上单元的指令集，此外还有许多其他功能.

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.

每次只需一点指令:

mrc p15, 0, %0, c9, c13, 0" : : "r" (counter)

根据 ARM Cortex A7 MPCore参考指令格式为:

MRC{cond} P15, <Opcode_1>, <Rd>, <CRn>, <CRm>, <Opcode_2>

在第4-11页上，这被描述为将CPU寄存器转移到性能监视器计数寄存器(我猜是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).

关于内联汇编器的语法.请参阅此以获取x86概述-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)表示指令具有:

• 寄存器中没有需要以局部变量结尾的输出
• 从变量counter获取输入，并且该寄存器所在的寄存器应用作%0.
• 编译器没有应注意的副作用(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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