patch.c

list of patches like:
	{CALL, &opt_hold,  1, 0x004101F8, hold_wrapper, 4},




#include <windows.h>
#include <stdint.h>
#include "patch.h"
#include "stdio.h"

enum err {
	ERR_UNHANDLED = -1,
	ERR_OK = 0,
	ERR_PERM,
	ERR_WRITE,
	ERR_MISMATCH
};

/* Do it! */
static enum err write_offset(uintptr_t in, void *out, size_t len)
{
	DWORD old;

	if(!VirtualProtect((void *)in, len, PAGE_READWRITE, &old))
		return ERR_PERM;
	
	if(!WriteProcessMemory(GetCurrentProcess(), (void *)in, &out, len, NULL))
		return ERR_WRITE;
	
	VirtualProtect((void *)in, len, old, &old);

	return ERR_OK;
}

static enum err write_array(uintptr_t in, void *out, size_t len)
{
	DWORD old;

	if(!VirtualProtect((void *)in, len, PAGE_READWRITE, &old))
		return ERR_PERM;
	
	if(!WriteProcessMemory(GetCurrentProcess(), (void *)in, out, len, NULL))
		return ERR_WRITE;
	
	VirtualProtect((void *)in, len, old, &old);

	return ERR_OK;
}

static enum err write_call(uintptr_t in, void *out, size_t len)
{
	unsigned char c;

	/* Check we're actually patching a call */
	c = *((unsigned char *)in);
	if(c != 0xE8)
		return ERR_MISMATCH;

	return write_offset(in+1, out-in-5, len);
}

static enum err write_jump(uintptr_t in, void *out, size_t len)
{
	unsigned char c;
	size_t i;

	/* Check we're actually patching some kind of jump */
	c = *((unsigned char *)in);
	if(c < 0x70 || c > 0x7B && (c != 0xE3 && c != 0xEB && c != 0xEB && c != 0xE9))
		return ERR_MISMATCH;

	return write_offset(in+1, out-in-5, len);
}

static enum err patch(struct patch p)
{
	enum err r = ERR_UNHANDLED;

	if(p.t == OFFS)
		r = write_offset(p.in, p.out, p.len);
	else if(p.t == CALL)
		r = write_call(p.in, p.out, p.len);
	else if(p.t == JUMP)
		r = write_jump(p.in, p.out, p.len);
	else if(p.t = ARRY)
		r = write_array(p.in, p.out, p.len);
	return r;
}

void do_patches(struct patch *p)
{
	size_t i;
	enum err r = ERR_OK;
	char buf[128];

	/* Apply all the patches in the list */
	for(i = 0; p[i].t; i++)
	{
		/* Patch is not enabled by config */
		if(p[i].p && *(p[i].p) < p[i].v)
			continue;

		r = patch(p[i]);
		if(r != ERR_OK) 
			break;
	}

	if(r == ERR_OK)
		return;

	/* Print nice error messages if a patch failed, then kill game.exe */
	switch(r)
	{
		char *s;

		case ERR_UNHANDLED:
			sprintf(buf, "Error: Unknown patch type %d {%p, %p}", p[i].t, p[i].in, (uintptr_t)p[i].out);
		break;
		case ERR_PERM:
			sprintf(buf, "Error: Could not unlock source address: %p", p[i].in);
		break;
		case ERR_WRITE:
			sprintf(buf, "Error: Could not write to address: %p (%d)", p[i].in);
		break;
		case ERR_MISMATCH:
				s = (p[i].t == CALL) ? "call" : "jump";
				sprintf(buf, "Error: %s patch for %p wasn't a %s instruction", s, p[i].in, s);
		break;
	}

	MessageBox(NULL, buf, "Failed to apply patch", MB_OK | MB_ICONERROR);
	TerminateProcess(GetCurrentProcess(), 1);
}