Question

我试图跟随this post中的代码，让信号处理程序打印出有关浮点和分段错误等错误的回溯。我使用seg故障信号作为起点。这是代码：

#include <cstdlib>      //for exit()
#include <signal.h>     //signal handling   
#include <execinfo.h>   //backtrace, backtrace_symbols and backtrace_fd
#include <iostream>
#include <string.h>
#include <stdio.h>

#define TRACE_MSG fprintf(stderr, "TRACE at: %s() [%s:%d]\n", \
        __FUNCTION__, __FILE__, __LINE__)

void show_stackframe()
{
    void *trace[1024];
    char **messages = (char **) NULL;
    int i, trace_size = 0;
    TRACE_MSG;
    trace_size = backtrace(trace, 1024);    // segfault here???
    // More code here to print backtrace, but not needed at the moment..
    TRACE_MSG;
}

void sigSegvHandler( int signum, siginfo_t* info, void* arg )
{
    TRACE_MSG;
    show_stackframe();
    return;
}

double func_b()
{
    show_stackframe();  // Show that backtrace works without being 
                    // called inside sighandler.

    TRACE_MSG;
    int int_a[5];
    int_a[0] = 4;
    int_a[11] = 10;         // cause a segfault on purpose to see
                    // how the signal handling performs.

    return 1.1;
}

int main()
{
    // Examine and change the seg fault signal
    struct sigaction segvAction;   // File: /usr/include/bits/sigaction.h

   // Initialize segvAction struct to all zeros for initialiation
   memset( &segvAction,  0, sizeof( segvAction ) );

   segvAction.sa_sigaction = sigSegvHandler;
   segvAction.sa_flags = SA_SIGINFO;    //Invoke signal catching function with 3 arguments instead of 1

   // Set the action for the SIGSEGV signal
   sigaction( SIGSEGV, &segvAction,  NULL );

   func_b();    // Produce a SIGSEGV error
}

我正在编译：

 g++ -rdynamic testprogram.cpp -o testprogram

我从程序中收到以下输出：

TRACE at: show_stackframe() [stackoverflow.cpp:15]
TRACE at: show_stackframe() [stackoverflow.cpp:17]
TRACE at: func_b() [stackoverflow.cpp:33]
TRACE at: sigSegvHandler() [stackoverflow.cpp:22]
TRACE at: show_stackframe() [stackoverflow.cpp:15]
Segmentation fault

我的问题是为什么show_stackframe（）会在sigaction中导致分段错误，但是当不在sigaction处理程序内部时工作正常？我显然似乎设置信号处理程序/操作不正确，但我还没有能够整天找到它。在这种情况下，GDB似乎没有任何帮助。

Answer 1

如上所述here，backtrace函数是AS不安全的，这意味着从异步信号处理程序调用是不安全的。这样做会调用未定义的行为。

信号处理程序内的Backtrace

1 个答案: