main.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <err.h>

#include <dasm_proto.h>
#include <dasm_x86.h>

Dst_DECL;

#include "dummy.c"

#define GLOB__MAX 8

static long get_page_size()
{
	static long sz;
	if (0 == sz)
		sz = sysconf(_SC_PAGESIZE);
	return sz;
}

static size_t round_up_to_page_size(size_t size)
{
	long sz = get_page_size();
	size_t remainder;
	remainder = size % sz;
	return size + sz - remainder;
}

static void *create_code_mapping(size_t size)
{
	void *ptr;
	size = round_up_to_page_size(size);
	ptr = mmap(NULL, size, PROT_READ | PROT_WRITE,
			MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
	if (MAP_FAILED == ptr)
		err(EXIT_FAILURE, "mmap");
	return ptr;
}

static void protect_code_mapping(void *addr, size_t size)
{
	int retval;
	size = round_up_to_page_size(size);
	retval = mprotect(addr, size, PROT_READ | PROT_EXEC);
	if (retval)
		err(EXIT_FAILURE, "mprotect");
}

static void destroy_code_mapping(void *ptr, size_t size)
{
	int retval;
	size = round_up_to_page_size(size);
	retval = munmap(ptr, size);
	if (retval)
		err(EXIT_FAILURE, "munmap");
}

int main() {
	int retval;
	void *buf;
	size_t size;
	int i;
	int nglob = GLOB__MAX;
	void **glob = (void **)malloc(nglob * sizeof(void *));
	int (*my_function)();
	memset(glob, 0x00, nglob * sizeof(void *));
	Dst = malloc(sizeof(*Dst));
	dasm_init(Dst, 10);
	dasm_setupglobal(Dst, glob, GLOB__MAX);
	dasm_setup(Dst, my_actionlist);
	create_my_function();
	retval = dasm_link(Dst, &size);
	printf("dasm_link returned %d\n", retval);
	buf = create_code_mapping(size);
	retval = dasm_encode(Dst, buf);
	printf("dasm_encode returned %d\n", retval);
	protect_code_mapping(buf, size);
	for (i = 0; i < nglob; i++)
		printf("glob[%d] = %p\n", i, glob[i]);
	my_function = (int (*)())glob[0];
	printf("going to call my_function\n");
	retval = my_function();
	printf("my_function has returned: %d\n", retval);
	destroy_code_mapping(buf, size);
	dasm_free(Dst);
	free(Dst);
	return 0;
}