/*
 * Quick simulation of what a JIT does.
 * This will not work on ELFv1.
 */
#include <sys/param.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <malloc_np.h>
#include <signal.h>

void *membuffer;

void zeroheader(void) __used;
void zeroret(void) __used;
void trailer(void) __used;

/* Begin template code. */

void
zeroheader()
{
	__asm __volatile ("nop;");
	return;
}

void zeroret()
{
	__asm __volatile ("nop;");
	return;
}

void
trailer()
{
	/* Do not call me -- function body not part of bcopy */
	__asm __volatile ("nop;");
}

/* End template code. */


/*
 * SIGSEGV handler to copy the function to the jit page AFTER
 * we have called it, to ensure all the moving parts are working.
 */
void
do_jit(void)
{
	mprotect(membuffer, 4096, PROT_READ|PROT_WRITE);
	memmove(membuffer, &zeroheader, MIN((&trailer - &zeroheader), 4096));
	__compiler_membar();
	mprotect(membuffer, 4096, PROT_READ|PROT_EXEC);
	return;
}

int
main(int argc, char *argv[])
{

	printf("Setting up page\n");

	membuffer = aligned_alloc(4096, 4096);
	if (!membuffer) {
		printf("Couldn't align buffer page");
		return(1);
	}

	printf("Buffer @ %p\n", membuffer);

	void (*callme)(void) = (void (*)(void))(membuffer + (&zeroret - &zeroheader));

	printf("Function pointer target: %p\n", &callme);

	signal(SIGSEGV, (sig_t)do_jit);
	printf("Signal handler installed.\n");
	mprotect(membuffer, 4096, PROT_NONE);
	printf("Protected JIT page. About to call.\n");

	/*
	 * At this point we are branching to an empty page with zero protections.
	 * The signal handler will copy the actual code over and fix up the protection.
	 */
	(callme)();

	/*
	 * Since we got here, everything is working properly.
	 */
	printf("Made it back to main().\n");

	return (0);
}