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.我有以下几个基本问​​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是 AArch32 还是 AArch64?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?

当前的异常级别是什么，EL0/1/2/3?

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

一旦出现异常，我是否可以读取任何寄存器来确定我是否在 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. 32 位和 64 位的汇编指令及其二进制编码完全不同.因此，您当前处于哪种模式的信息是您/编译器在编译期间已经需要知道的信息.在运行时检查它们没有意义.对于 C，C++ 检查可以在编译时 (#ifdef) 通过编译器提供的宏完成，例如 armclang 提供的宏:__aarch64__ for 64位，__arm__ 为 32 位
2. 取决于执行模式:
   • aarch32:MRS , CPSR 将当前状态读入寄存器编号 n.然后提取包含当前模式的位 3:0.
   • aarch64:MRS , CurrentEL 将当前 EL 读入寄存器编号 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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