为什么WIFSIGNALED（状态）无法检测到信号，同时跟踪与ptrace的一个过程？

问题描述

我使用ptrace的跟踪子进程。它的工作原理非常清楚，当子进程正常退出。但是，如果它退出异常，程序进入在尽管使用宏WIFSIGNALED（安培;状态）的无限循环。下面是示例子进程：

I am using ptrace to trace a child process. It works perfectly well when the child process exit normally. But if it exit abnormally, the program get into an infinite loop in-spite of using the macro WIFSIGNALED(&status). Here is sample child process:

try.c

int main()
   {
      int a=5/0;
   }

和这里追踪程序

#include <sys/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <sys/user.h>
#include <sys/syscall.h>   /* For SYS_write etc */
#include <sys/reg.h>
#include <signal.h>
int main()
{   
    pid_t child;
    long orig_eax, eax;
    int status,insyscall = 0;
    child = fork();
    if(child == 0)
    {
            ptrace(PTRACE_TRACEME, 0, NULL, NULL);
            execl("./try", "try", NULL);
    }
    else
    {
        siginfo_t sig;
        memset(&sig,0,sizeof(siginfo_t));
        while(1)
        {
            wait(&status);
            if(WIFSIGNALED(status))
            {
                printf("Exiting due to signal\n");
                exit(0);
            }
            if(WIFEXITED(status))
                break;
            orig_eax = ptrace(PTRACE_PEEKUSER,child, 4 * ORIG_EAX, NULL);
            printf("system call number=%ld\n",orig_eax);
            if(insyscall == 0)
            {
                      /* Syscall entry */
                      insyscall = 1;
                      printf("In sys call\n");
            }
            else 
            {
               /* Syscall exit */
                 eax = ptrace(PTRACE_PEEKUSER,child, 4 * EAX, NULL);
                 printf("System call returned with %ld\n", eax);
                 insyscall = 0;
             }
            ptrace(PTRACE_SYSCALL,child, NULL, NULL);
        }
    }
    return 0;
}

为什么没有被检测到的信号，否则工作时不使用的ptrace

Why the signal is not being detected which otherwise works when ptrace is not used?

推荐答案

在ptrace的一个过程，等待返回任何状态变化。其中之一是当处理即将接收信号。你的等待将返回的前的信号被传递到子。您需要使用PTRACE_CONT允许信号被传递给孩子，如果这就是你要发生什么。

When you ptrace a process, wait will return for any state change. One of those is when the process is about to receive a signal. Your wait will return before the signal is delivered to the child. You need to use PTRACE_CONT to allow the signal to be delivered to the child, if that's what you want to happen.

为什么它这样工作？清楚地记得，ptrace的主要目的是在实施调试器使用。如果你没有得到一个机会来截取信号，如 SIGSEGV ，调试器不能停下来让你检查赛格故障的过程中被拆掉了。

Why does it work this way? Well remember, ptrace's main purpose is to be used in implementing debuggers. If you didn't get a chance to intercept signals such as SIGSEGV, the debugger couldn't stop and let you examine the seg fault before the process was torn down.

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