CLONE_SIGHAND example

This post we will write a code, which will give us an observation what changes when CLONE_SIGHAND is added and when it is removed.

Code:

	#define _GNU_SOURCE
	#include <stdio.h>
	#include <sys/types.h>
	#include <fcntl.h>
	#include <sched.h>
	#include <stdlib.h>
	#include <string.h>
	#include <unistd.h>
	#include <sys/wait.h>
	#include <signal.h>
	#define STACK_SIZE 65536
	int catch_signal;
	struct sigaction sa;
	static void sighandler(int sig)
	{
	printf("Caught signal %d (%s) \n", sig, strsignal(sig));
	}
	static int child_func(void *arg)
	{
	signal(catch_signal, sighandler);
	kill(getpid(), SIGTERM);
	return 0;
	}
	int main(int argc, char *argv[])
	{
	//Allocate stack for child task
	char *stack = malloc(STACK_SIZE);
	unsigned long flags = 0;
	char buf[256];
	int status;
	catch_signal = SIGTERM;
	if (signal(catch_signal, SIG_IGN) == SIG_ERR) {
	perror("signal");
	exit(1);
	}
	if (!stack) {
	perror("Failed to allocate memory\n");
	exit(1);
	}
	if (argc == 2 && !strcmp(argv[1], "signal"))
	flags |= CLONE_SIGHAND;
	if (clone(child_func, stack + STACK_SIZE, flags | CLONE_VM |SIGCHLD, NULL) == -1) {
	perror("clone");
	exit(1);
	}
	if (wait(&status) == -1) {
	perror("Wait");
	exit(1);
	}
	printf("Child exited with status:%d\n", status);
	kill(getpid(), SIGTERM);
	return 0;
	}

view raw clone_signal.c hosted with ❤ by GitHub

Output:

Notes:

You can see from the code, when CLONE_SIGHAND was set, parent modifying the default behavior of SIGTERM affected the parent process, and it did not ignore the SIGTERM signal and instead called the signal handler.