当前的执行模式/异常级别等是什么？ [英] what is the current execution mode/exception level, etc?

问题描述

我是ARMv8架构的新手。我心中有以下基本问题：

I am new to ARMv8 architecture. I have following basic questions on my mind:

1. 我如何知道当前的执行模式AArch32或AArch64是什么？我应该阅读CPSR还是SPSR来确定这一点？

1. How do I know what is the current execution mode AArch32 or AArch64? Should I read CPSR or SPSR to ascertain this?

当前的异常级别EL0 / 1/2/3是什么？

What is the current Exception level, EL0/1/2/3?

一旦出现异常，我可以读取任何寄存器以确定我是否处于Serror / Synchronous / IRQ / FIQ异常处理程序中。

Once an exception comes, can i read any register to determine whether I am in Serror/Synchronous/IRQ/FIQ exception handler.

TIA。

推荐答案

1. 程序集32位和64位的指令及其二进制编码完全不同。因此，您当前所处模式的信息是您/编译器在编译过程中已经需要知道的。在运行时检查它们没有任何意义。对于C语言，可以在编译时（ #ifdef ）通过编译器提供的宏（例如 armclang ： __ aarch64 __ （用于64位）， __ arm __ （用于32位）


2. 取决于执行模式：
   
   
   
   
   • aarch32： MRS< Rn> ;, CPSR 将当前状态读入寄存器数然后提取包含当前模式的3：0位。
   
   
   • aarch64： MRS< Xn>，CurrentEL 将当前EL读入注册号n
   
   

1. The assembly instructions and their binary encoding are entirely different for 32 and 64 bit. So the information what mode you are currently in is something that you/ the compiler already needs to know during compilation. checking for them at runtime doesn't make sense. For C, C++ checking can be done at compile time (#ifdef) through compiler provided macros like the ones provided by armclang: __aarch64__ for 64 bit, __arm__ for 32 bit
2. depends on the execution mode:
   • aarch32: MRS <Rn>, CPSR read the current state into register number n. Then extract bits 3:0 that contain the current mode.
   • aarch64: MRS <Xn>, CurrentEL read the current EL into register number n

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