GDB调试之信号

清疚 2022-08-29 15:48 277阅读 0赞

# **目录** #

*  GDB发送信号
 *  GDB对信号的处理
 *  实例

# **GDB发送信号** #

在GDB调试状态中，可以在命令号输入`signal 信号`来向程序发送信号

# **GDB处理信号** #

> 背景：GDB调试时，能够捕获产生的信号并停止，当频繁有信号产生时，很影响调试

在GDB中handle指令用于设置GDB对于信号的处理，可以输入`help handle`来查看

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 <td style="text-align:left;vertical-align:middle;"> <pre style="margin-left:0;">Specify&nbsp;how&nbsp;to&nbsp;handle&nbsp;signals.
Usage:&nbsp;handle&nbsp;SIGNAL&nbsp;[ACTIONS]
Args&nbsp;are&nbsp;signals&nbsp;and&nbsp;actions&nbsp;to&nbsp;apply&nbsp;to&nbsp;those&nbsp;signals.
If&nbsp;no&nbsp;actions&nbsp;are&nbsp;specified,&nbsp;the&nbsp;current&nbsp;settings&nbsp;for&nbsp;the&nbsp;specified&nbsp;signals
will&nbsp;be&nbsp;displayed&nbsp;instead.
Symbolic&nbsp;signals&nbsp;(e.g.&nbsp;SIGSEGV)&nbsp;are&nbsp;recommended&nbsp;but&nbsp;numeric&nbsp;signals
from&nbsp;1-15&nbsp;are&nbsp;allowed&nbsp;for&nbsp;compatibility&nbsp;with&nbsp;old&nbsp;versions&nbsp;of&nbsp;GDB.
Numeric&nbsp;ranges&nbsp;may&nbsp;be&nbsp;specified&nbsp;with&nbsp;the&nbsp;form&nbsp;LOW-HIGH&nbsp;(e.g.&nbsp;1-5).
The&nbsp;special&nbsp;arg&nbsp;"all"&nbsp;is&nbsp;recognized&nbsp;to&nbsp;mean&nbsp;all&nbsp;signals&nbsp;except&nbsp;those
used&nbsp;by&nbsp;the&nbsp;debugger,&nbsp;typically&nbsp;SIGTRAP&nbsp;and&nbsp;SIGINT.
Recognized&nbsp;actions&nbsp;include&nbsp;"stop",&nbsp;"nostop",&nbsp;"print",&nbsp;"noprint",
"pass",&nbsp;"nopass",&nbsp;"ignore",&nbsp;or&nbsp;"noignore".
Stop&nbsp;means&nbsp;reenter&nbsp;debugger&nbsp;if&nbsp;this&nbsp;signal&nbsp;happens&nbsp;(implies&nbsp;print).
Print&nbsp;means&nbsp;print&nbsp;a&nbsp;message&nbsp;if&nbsp;this&nbsp;signal&nbsp;happens.
Pass&nbsp;means&nbsp;let&nbsp;program&nbsp;see&nbsp;this&nbsp;signal;&nbsp;otherwise&nbsp;program&nbsp;doesn't&nbsp;know.
Ignore&nbsp;is&nbsp;a&nbsp;synonym&nbsp;for&nbsp;nopass&nbsp;and&nbsp;noignore&nbsp;is&nbsp;a&nbsp;synonym&nbsp;for&nbsp;pass.
Pass&nbsp;and&nbsp;Stop&nbsp;may&nbsp;be&nbsp;combined.
Multiple&nbsp;signals&nbsp;may&nbsp;be&nbsp;specified.&nbsp;&nbsp;Signal&nbsp;numbers&nbsp;and&nbsp;signal&nbsp;names
may&nbsp;be&nbsp;interspersed&nbsp;with&nbsp;actions,&nbsp;with&nbsp;the&nbsp;actions&nbsp;being&nbsp;performed&nbsp;for
all&nbsp;signals&nbsp;cumulatively&nbsp;specified.
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总结大体意思：

*  **nostop**  
    当被调试的程序收到信号时，GDB不会停住程序的运行，但会打出消息告诉你收到这种信号。
 *  **stop**  
    当被调试的程序收到信号时，GDB会停住你的程序。
 *  **print**  
    当被调试的程序收到信号时，GDB会显示出一条信息。
 *  **noprint**  
    当被调试的程序收到信号时，GDB不会告诉你收到信号的信息。
 *  **pass** 、**noignore**  
    当被调试的程序收到信号时，GDB不处理信号。这表示，GDB会把这个信号交给被调试程序会处理。
 *  **nopass**、**ignore**  
    当被调试的程序收到信号时，GDB不会让被调试程序来处理这个信号

在GDB中可以使用`info signals`和`info handle`来查看有哪些信号在被GDB检测中和GDB对其的处理

SIGHUP Yes Yes Yes Hangup
SIGINT Yes Yes No Interrupt
SIGQUIT Yes Yes Yes Quit
SIGILL Yes Yes Yes Illegal instruction
SIGTRAP Yes Yes No Trace/breakpoint trap
SIGABRT Yes Yes Yes Aborted
SIGEMT Yes Yes Yes Emulation trap
SIGFPE Yes Yes Yes Arithmetic exception
SIGKILL Yes Yes Yes Killed
SIGBUS Yes Yes Yes Bus error
SIGSEGV Yes Yes Yes Segmentation fault
...
SIGUSR1 Yes Yes Yes User defined signal 1
SIGUSR2 Yes Yes Yes User defined signal 2

还有很多不列出。
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# **实例** #

例程代码如下

void signalHandle2(int para)
{
 printf("in signal handle,signal num:%d\n", para);
 exit(0);
}

int main(void)
{
 signal(SIGUSR1, signalHandle);
 signal(SIGUSR2, signalHandle2);

while(1)
 {
 printf("press any key to send a signal\n");
 getchar();
 raise(SIGUSR1);
 }

return 0;
}
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为了效果更佳明显，先运行程序，然后gdb attach到进程上，进入gdb调试模式

Program received signal SIGUSR1, User defined signal 1.
0x00007fd1f1ec9337 in raise () from /lib64/libc.so.6
(gdb) c
Continuing.
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可以发现当在程序中按下回车时，进程给自己发送了SIGUSR1信号，并且GDB捕获到该信号切停下，我们继续运行，  
将GDB对SIGUSR1信号的处理设置为nostop

Program received signal SIGUSR1, User defined signal 1
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可以发现此时只会打印，而gdb不会停下，接下来  
将GDB对SIGUSR1信号的处理设置为noprint

此时GDB既不会打印也不会停下

通过GDB给程序发送信号

程序命令行打印in signal handle,signal num:12,显然收到SIGUSR2信号

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