gistfile1.h

/*
    My very own setjmp.
*/

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

typedef struct Continuation {
	void* rip;
	void* rsp;
	void* rbp;
} Continuation;

void resume(Continuation* cc)
{
	__asm__(
		// restore registers
		"movq %0, %%rdi\n"
		"movq %1, %%rsp\n"
		"movq %2, %%rbp\n"
		"movq %3, %%r8\n"
		"movq $1, %%rax\n"
		// resume!
		"jmpq *%%r8\n"
	:
	: "r"(cc), "m"(cc->rsp), "m"(cc->rbp), "m"(cc->rip)
	: "%rdi", "%rsi", "%rsp", "%rbp", "%r8"
	);
}

bool save(Continuation* cc)
{
	__asm__(
	// rsp is rsp, since the stack size of this function is 0
	"movq %%rsp, %0\n"
	// rbp stored on the stack
	"movq (%%rsp), %%rax\n"
	"movq %%rax, %1\n"
	 // read instruction pointer for calling function from the stack
	"movq %%rbp, %%r8\n"
	"movq 8(%%r8), %%rax\n"
	"movq %%rax, %2\n"
	: "=m"(cc->rsp), "=m"(cc->rbp), "=m"(cc->rip)
	:
	: "%rax"
	);
	return false;
}



int main (int argc, char const *argv[])
{
	Continuation cc;
	printf("cc is at 0x%llx\n", &cc);
	printf("before\n");
	if (save(&cc)) {
		printf("returned from continuation!\n");
		printf("muuuh\n");
	} else {
		printf("returning directly\n");
		resume(&cc);
		printf("after resume -- should never be reached!\n");
	}
	printf("exiting\n");
	return 0;
}