1.5.runtime.c

#include <stdio.h>
#include <stdlib.h>  // for exit
#include <sys/mman.h>

extern int scheme_entry(void* stack);

/* define all scheme constatns */
#define	bool_f		0x2f
#define	bool_t		0x6f
#define	fx_mask		0x03
#define	fx_tag		0x00
#define	fx_shift	2
#define	nullval		0x3f
#define	char_mask	0xff
#define	char_shift	8
#define	char_tag	0x0f

/* all scheme values are of type ptrs */
typedef unsigned int ptr;

static void print_ptr(ptr x) {
	if ((x & fx_mask) == fx_tag) {
		printf("%d", ((int)x) >> fx_shift);
	} else if (x == bool_f) {
		printf("#f");
	} else if (x == bool_t) {
		printf("#t");
	} else if (x == nullval) {
		printf("()");
	} else if ((x & char_mask) == char_tag) {
		int c = x >> char_shift;
		switch (c) {
		default:	printf("#\\%c", c);	break;
		case '\t':	printf("#\\tab");	break;
		case '\n':	printf("#\\newline");	break;
		case '\r':	printf("#\\return");	break;
		case ' ':	printf("#\\space");	break;
		}
	} else {
		printf("#<unknown #0x%08x>", x);
	}
	printf("\n");
}

static char* allocate_protected_space(int size) {
	int page = getpagesize();
	int status;
	int aligned_size = ((size + page - 1) / page) * page;
	char* p = mmap(0, aligned_size + 2 * page, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
	if (p == MAP_FAILED) { exit(1); }
	status = mprotect(p, page, PROT_NONE);
	if (status != 0) { exit(1); }
	status = mprotect(p + page + aligned_size, page, PROT_NONE);
	if (status != 0) { exit(1); }
	return p + page;
}

static void deallocate_protected_space(char* p, int size) {
	int page = getpagesize();
	int status;
	int aligned_size = ((size + page - 1) / page) * page;
	status = munmap(p - page, aligned_size + 2 * page);
	if (status != 0) { exit(1); }
}

int main(int argc, char** argv) {
	int stack_size = (128 * 4096);	/* holds 128K cells */
	char* stack_top = allocate_protected_space(stack_size);
	char* stack_base = stack_top + stack_size;
	print_ptr(scheme_entry(stack_base));
	deallocate_protected_space(stack_top, stack_size);
	return 0;
}