“零分"在哪里?在Arm Cortex A-9的内核中完成 [英] Where is the "Zero divide" done in kernel for Arm Cortex A-9

问题描述

我正在研究用于零除的内核源代码(2.6.35).

I am looking into kernel source code (2.6.35 ) for Zero divide .

我在用户空间程序中插入了零除，并且所有线程都停止了.

I inserted Zero divide in user space program and all threads stopped.

所以我想知道Arm Cortex A-9的内核中的零除"在哪里?

So I want to know Where is the "Zero divide" done in kernel for Arm Cortex A-9?

我无法为此找到任何陷阱....

I am not able to find any trap for this ....

谢谢

推荐答案

这取决于体系结构.在 x86系统上给定以下用户空间代码:

It depends on the architecture. Given the following user space code on an x86 system:

main() {                                                                                                                                                                             
   int x = 42 / 0;                                                                                                                                                                   
}                                                                                                                                                                                    

编译器在目标代码中插入一个idivl命令.当该命令的除数为0执行时，CPU会生成一个除以零的陷阱(类似于中断).这会在内核内部调用divide_error陷阱处理程序，在x86的情况下，它位于arch/x86/kernel/entry_32.S中:

the compiler inserts a idivl command into the object code. When this command is executed with a divisor of 0, the CPU generates a division by zero trap (similar to an interrupt). This calls the divide_error trap handler inside the kernel, in case of x86 it is located in arch/x86/kernel/entry_32.S:

ENTRY(divide_error)
        RING0_INT_FRAME
        pushl_cfi $0                    # no error code
        pushl_cfi $do_divide_error
        jmp error_code
        CFI_ENDPROC
END(divide_error)

然后，error_code目标执行所有必要的操作以处理错误，并最终从陷阱返回.

The error_code target then takes care of all necessary actions to handle the error and finally returns from the trap.

在 ARM 上，情况有所不同:除少数例外， ARM CPU没有硬件划分指令(例如Arm Cortex A-9没有硬件划分指令).除法需要实现为库功能.对于内核，这是在arch/arm/lib/lib1funcs.S中实现的，您还可以在其中找到被零处理的除法.对于用户空间应用程序，我想这是作为libgcc库中的库函数实现的.

On ARM, things are different: With a few exceptions, ARM CPUs do not have a hardware division instruction (e.g. Arm Cortex A-9 does not have one). Division needs to be implemented as a library function. For the kernel, this is implemented in arch/arm/lib/lib1funcs.S where you also find the division by zero handling. For user space applications, I suppose this is implemented as a library function in the libgcc library.

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