Exercise integer-pointer type confusion bug

This exercise demonstrates how CHERI distinguishes between integer and pointer types, preventing certain types of type confusion. In this example, a union allows an integer value to be used as a pointer, which cannot then be dereferenced.

1. Compile type-confusion.c with a RISC-V target and binary name of type-confusion-riscv, and with a CHERI-RISC-V target and binary name type-confusion-cheri.

type-confusion.c

/*
 * SPDX-License-Identifier: BSD-2-Clause-DARPA-SSITH-ECATS-HR0011-18-C-0016
 * Copyright (c) 2020 SRI International
 */
#include <printf.h>

const char hello[] = "Hello World!";

union long_ptr {
	long l;
	const char *ptr;
} lp = { .ptr = hello };

void
inc_long_ptr(union long_ptr *lpp)
{
	lpp->l++;
}

void
init(void)
{
	printf("lp.ptr %s\n", lp.ptr);
	inc_long_ptr(&lp);
	printf("lp.ptr %s\n", lp.ptr);
}

void notified(void){}

1. Run the RISC-V program. What is the result?

2. Run the CHERI-RISC-V program. What is the result? Run under QEMU and gdb and explain why the program crashes in the second printf.