崩溃期间未捕获到SIGSEGV信号

Question

I am trying to run a code that will generate a segmentation fault. But the segmentation fault is not generated.

int main()
{

char *variable;

strcpy(variable,"hello");

}

The program crashes but the message saying that a segmentation violation has occurred is not getting displayed .

Even when I write a signal handler to handle the segmentation fault , the signal is not getting caught.

Do you know why this is occurring ? Is there any chance that the handling of the SIGSEGV signal by the kernel would have been disabled or something...

Thanks,

Answer 1

In my case, the segmentation fault has come using gcc compiler(Output : Segmentation fault). But if in your case its not coming , try running your binary using strace like strace ./a.out(say). It will show the the system level command executed on the console. May be u will get an idea from this

Answer 2

First, you really should get the habit of compiling with gcc -Wall which warns against such mistakes.

And to understand what really is happening, use a debugger like gdb to run your code step by step. You might also use strace or better ltrace (which would show the argument to strcpy ).

Then, a possible explanation (just a guess) might be the following:

• your variable is uninitialized

• so it keeps the "value" that the register (or stack slot) storing that variable had previously

• main is called by crt0.o which happens to initialize that location with something meaningful (a valid pointer), perhaps argv[0] of main or some shell environment variable

(You could read more about x86-64 ABI to understand how crt0.o sets the stack)

If you initialize variable=NULL; you'll get a SIGSEGV