dbg1.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/ptrace.h>
#include <sys/types.h>
#include <unistd.h>
#include <assert.h>
#include <signal.h>

void hello() {
	printf("Hello debugger\n");
}

main() {
	int ret;
	pid_t child;


	child = fork();
	if (!child) {
		sleep(2);

		printf("Running child\n");
		hello();
		exit(0);
	}

	ret = ptrace(PTRACE_ATTACH, child, 0L, 0L);
	assert(ret == 0);

	waitpid(child, &ret, 0);

	unsigned char bp[8];
	memset(&bp, 0xcc, 8);

	ret = ptrace(PTRACE_POKEDATA, child, &hello, (void*) &bp);
	assert(ret == 0);

	ret = ptrace(PTRACE_CONT, child, 0L, 0L);
	assert(ret == 0);

	exit(1);
	//waitpid(child, &ret, 0);
	//printf("Parent done\n");
}