ARM中是否有与rdtsc等效的指令?

2022-01-17 00:00:00 c assembly arm c++ inline-assembly

对于我的项目我必须使用rdtsc等内联汇编指令来计算一些C/C++指令的执行时间.

For my project I must use inline assembly instructions such as rdtsc to calculate the execution time of some C/C++ instructions.

以下代码似乎适用于 Intel，但不适用于 ARM 处理器:

The following code seems to work on Intel but not on ARM processors:

{unsigned a, d;asm volatile("rdtsc" : "=a" (a), "=d" (d)); t0 = ((unsigned long)a) | (((unsigned long)d) << 32);}
//The C++ statement to measure its execution time
{unsigned a, d;asm volatile("rdtsc" : "=a" (a), "=d" (d)); t1 = ((unsigned long)a) | (((unsigned long)d) << 32);}
time = t1-t0;

我的问题是:

如何编写类似于上述的内联汇编代码(计算一条指令的执行时间)在ARM处理器上工作?

How to write an inline assembly code similar to the above (to calculate the execution elapsed time of an instruction) to work on ARM processors?

推荐答案

你应该读取协处理器 p15 的 PMCCNTR 寄存器(不是真正的协处理器，只是 CPU 函数的入口点)来获取循环计数.请注意，只有在以下情况下，它才可用于非特权应用:

You should read the PMCCNTR register of a co-processor p15 (not an actual co-processor, just an entry point for CPU functions) to obtain a cycle count. Note that it is available to an unprivileged app only if:

  1. 允许非特权 PMCCNTR 读取:

PMUSERENR 寄存器的位 0 必须设置为 1 (官方文档)

Bit 0 of PMUSERENR register must be set to 1 (official docs)

PMCCNTR 实际上是在计算周期:

PMCCNTR is actually counting cycles:

PMCNTENSET 寄存器的第 31 位必须设置为 1 (官方文档)

Bit 31 of PMCNTENSET register must be set to 1 (official docs)

这是一个真实的例子 它是如何完成的.

This is a real-world example of how it`s done.

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