Got a segmentation fault due to null pointer dereferencing? No worry, just skip over it #yolo

nullptr-shenanigans.c

// build and run with:
//   $ gcc nullptr-shenanigans.c -Wall -Wextra -pedantic -std=c99 -O0 -o lol
//   $ ./lol

// expected output:
//   Got SIGSEGV at address: 0x0 (REG_RIP = 93937079497465)
//   This should not print: p = (nil)?
//   Allright then, we are done!

#define _GNU_SOURCE 1  /* To pick up REG_RIP */

#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <ucontext.h>

static void handler(int signo, siginfo_t *info, void *context)
{
	(void)signo;
	ucontext_t * ctx = (ucontext_t *)context;

	printf("Got SIGSEGV at address: 0x%lx (REG_RIP = %lld)\n",
			(long) info->si_addr,
			ctx->uc_mcontext.gregs[REG_RIP]);

	// Let's just adjust the instruction pointer and skip over the offending instructions *shrug* 
	// You may need to adjust the offset based on your architecture ('6' works on x86_64).
        // Also, using any other optimization beyond -O0 level will break this
	ctx->uc_mcontext.gregs[REG_RIP] += 6;
}

int main(){
	struct sigaction sa;

	sa.sa_flags = SA_SIGINFO;
	sigemptyset(&sa.sa_mask);
	sa.sa_sigaction = handler;

	if (sigaction(SIGSEGV, &sa, NULL) == -1){
		perror("sigaction");
		abort();
	}

	int * p = NULL;

	*p = 11;  // HUH??

	printf("This should not print: p = %p?\n", (void*)p);

	printf("Allright then, we are done!\n");
}