Question

在我的下面的代码中，如果我将old_act声明为全局变量，那么程序运行正常。如果在main中声明：

如果使用SA_RESTART，则可以正常使用
如果未使用SA_RESTART，则会导致分段错误。

有人可以帮助我理解发生的事情。

void sighandler(int signum)
{
        printf("Caught signal:%d pressed ctrl+c!!\n",signum);
}

int main()
{
        struct sigaction act_h;
        struct sigaction old_act;
        act_h.sa_handler = sighandler;
//      act_h.sa_flags = SA_RESTART;

       sigaction(SIGINT,&act_h,&old_act);

        printf("This is an infinite loop\n");
        int remain=sleep(10);
        printf("remaining time in sec : %d\n",remain);
        printf("Before second sleep\n");
        sleep(10);
        printf("This is an infinite loop\n");
        return 0;
}

从gdb看起来，某些函数调用发生在非法位置，但不确定：

This GDB was configured as "i686-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/diwakar/Documents/my_C_codes/L2IT/SigHandling/a.out...done.
[New LWP 5661]

warning: Can't read pathname for load map: Input/output error.
Core was generated by `./a.out'.
Program terminated with signal 11, Segmentation fault.
#0  0xb77c1938 in ?? ()
(gdb) 


(gdb) bt
#0  0xb77c1938 in ?? ()
Cannot access memory at address 0xe


(gdb) run
Starting program: /home/diwakar/Documents/my_C_codes/L2IT/SigHandling/a.out 
This is an infinite loop
^C
Program received signal SIGINT, Interrupt.
0xb7fdd424 in __kernel_vsyscall ()
(gdb) bt
#0  0xb7fdd424 in __kernel_vsyscall ()
#1  0xb7ed2f00 in nanosleep () from /lib/i386-linux-gnu/libc.so.6
#2  0xb7ed2d1f in sleep () from /lib/i386-linux-gnu/libc.so.6
#3  0x08048502 in main () at signal.c:33
(gdb) disassemble
Dump of assembler code for function __kernel_vsyscall:
   0xb7fdd414 <+0>: push   %ecx
   0xb7fdd415 <+1>: push   %edx
   0xb7fdd416 <+2>: push   %ebp
   0xb7fdd417 <+3>: mov    %esp,%ebp
   0xb7fdd419 <+5>: sysenter 
   0xb7fdd41b <+7>: nop
   0xb7fdd41c <+8>: nop
   0xb7fdd41d <+9>: nop
   0xb7fdd41e <+10>:    nop
   0xb7fdd41f <+11>:    nop
   0xb7fdd420 <+12>:    nop
   0xb7fdd421 <+13>:    nop
   0xb7fdd422 <+14>:    int    $0x80
=> 0xb7fdd424 <+16>:    pop    %ebp
   0xb7fdd425 <+17>:    pop    %edx
   0xb7fdd426 <+18>:    pop    %ecx
   0xb7fdd427 <+19>:    ret    
End of assembler dump.
(gdb)

Answer 1

尝试在分配之前将act_h的所有成员重置为零。很可能sa_flags具有一些随机值，这使得信号操作表现得不同。

int main()
{
        struct sigaction act_h;
        struct sigaction old_act;

        //reset all members
        memset(&act_h, 0, sizeof(act_h));
        act_h.sa_handler = sighandler;
        .... //continue your code;

}

Answer 2

您必须使用一个sigemptyset()或sigfillset()来初始化信号集。或者，在您的具体情况中：

sigemptyset(&act_h.sa_mask);

在你的情况下，请记住C没有像“默认构造函数”之类的东西。因此，信号集和其他自动变量不会自动初始化，很可能包含垃圾值。

另外，请注意，直接将所讨论的结构设置为零是正确初始化空信号集的不可靠方法。

sigaction信号处理程序中的分段错误

2 个答案: