setjmp experiments

broken_stackframe_setjmp.c

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

typedef unsigned long long __u64;

#define get_rsp(into) \
	__asm__ __volatile__("movq %%rsp, %0;" : "=m"(into) :: "memory")

#ifndef PUSH_RET_ADDR
# define __maybe_noreturn __attribute__((noreturn))
#else
# define __maybe_noreturn
#endif

static jmp_buf env;

void setter() {
	__u64 rsp;
	get_rsp(rsp);
	
	int x = 0xcafebabe;
	
	if(setjmp(env) == 1) {
		get_rsp(rsp);
		printf("setter(rsp=0x%x): refetched rsp\n", rsp);
	}

	printf("setter(rsp=0x%x): \"x\" has value 0x%x\n", rsp, x);
}

__maybe_noreturn void jumper() {
	__u64 rsp;
	get_rsp(rsp);
	
	int y = 0xdeadbeef;
	
	printf("jumper(rsp=0x%x): performing long jump\n", rsp);
	longjmp(env, 1);
}

int main() {
	setter();
	jumper();

	puts("gracefully exiting...");
	
	return EXIT_SUCCESS;
}

raii_violation_setjmp.cpp

#include <iostream>
#include <csetjmp>

#ifdef MAKE_LONGJMP
# define __maybe_noreturn __attribute__((noreturn))
# define __maybe_longjmp(b,v) longjmp(b,v)
#else
# define __maybe_noreturn
# define __maybe_longjmp(unused_1, unused_2)
#endif

static jmp_buf env;

class ResourceHolder {
public:
	ResourceHolder() {
		std::cout << "\t\tResourceHolder::<ctor> -- acquisition\n";
	}

	~ResourceHolder() {
		std::cout << "\t\tResourceHolder::<dtor> -- release\n";
	}
};

__maybe_noreturn void f() {
	ResourceHolder r;
	__maybe_longjmp(env, 1);
}

int main() {
	std::cout << "starting\n";

	if(!setjmp(env)) {
		std::cout << "\tenv set nonlocal jump\n\tcalling f()\n";
		f();
		std::cout << "\tback from f() via ret instruction execution\n";
	} else {
		std::cout << "\tback from f() via long jump\n";
	}

	std::cout << "exiting...\n";

	return 0;
}