Interruptible VM with signal handlers

gistfile1.c

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

typedef enum opcode {
	OP_HALT = 0,
	OP_NOP,
	OP_JMP,
	OP_MAX
} opcode_t;

typedef struct ins {
	char i;
	char o;
} ins_t;

void **jump_table_hack;
void exec(ins_t*, void***);

static void catch_signal(int signo) {
	puts("abort requested!\n");
	// caught a SIGINT - rewrite the opcode handlers so that
	// every instruction is handled as OP_HALT - this forces
	// the VM to exit with clobbering the input program
	for (int i = 1; i < OP_MAX; ++i) {
		jump_table_hack[i] = jump_table_hack[0];
	}
}

int main(int argc, char *argv[]) {
	
	// steal the jump table so the signal handler
	// can rewrite it to force program abort
	exec(NULL, &jump_table_hack);
	
	// program that loops forever
	ins_t myprog[] = {
		{ OP_NOP, 0 },
		{ OP_JMP, 0 }
	};
	
	// install signal handler
	if (signal(SIGINT, catch_signal) == SIG_ERR) {
		fputs("boom\n", stderr);
		return EXIT_FAILURE;
	}
	
	// run the program
	exec(myprog, NULL);
	
	return 0;
	
}

void exec(ins_t *program, void ***jump_table_out) {
	
	static void *jump_table[] = {
		&&L_HALT,
		&&L_NOP,
		&&L_JMP
	};
	
	if (jump_table_out) {
		*jump_table_out = (void**)&jump_table;
		return;
	}
	
	int ip = 0;
	goto *(jump_table[program[ip].i]);
	
	L_HALT:
		puts("interpreter exited gracefully!\n");
		return;
	
	L_NOP:
		printf("NOP!\n");
		goto *jump_table[program[++ip].i];
	
	L_JMP:
		ip = program[ip].o;
		goto *jump_table[program[ip].i];

}