/**
 * vim: set ts=4 :
 * =============================================================================
 * SourceMod
 * Copyright (C) 2004-2010 AlliedModders LLC.  All rights reserved.
 * =============================================================================
 *
 * This program is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License, version 3.0, as published by the
 * Free Software Foundation.
 * 
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * As a special exception, AlliedModders LLC gives you permission to link the
 * code of this program (as well as its derivative works) to "Half-Life 2," the
 * "Source Engine," the "SourcePawn JIT," and any Game MODs that run on software
 * by the Valve Corporation.  You must obey the GNU General Public License in
 * all respects for all other code used.  Additionally, AlliedModders LLC grants
 * this exception to all derivative works.  AlliedModders LLC defines further
 * exceptions, found in LICENSE.txt (as of this writing, version JULY-31-2007),
 * or <http://www.sourcemod.net/license.php>.
 *
 * Version: $Id: detourhelpers.h 248 2008-08-27 00:56:22Z pred $
 */

#ifndef _INCLUDE_SOURCEMOD_DETOURHELPERS_H_
#define _INCLUDE_SOURCEMOD_DETOURHELPERS_H_

#if defined PLATFORM_POSIX
#include <sys/mman.h>
#define	PAGE_EXECUTE_READWRITE	PROT_READ|PROT_WRITE|PROT_EXEC
#endif

#include <amtl/am-bits.h>
#include <jit/x86/x86_macros.h>
#include <amtl/os/am-system-errors.h>
#include <cstdio>

struct patch_t
{
	patch_t()
	{
		patch[0] = 0;
		bytes = 0;
	}
	unsigned char patch[20];
	size_t bytes;
};

inline void ProtectMemory(void *addr, int length, int prot)
{
	char error[256];
#if defined PLATFORM_POSIX
	long pageSize = sysconf(_SC_PAGESIZE);
	void *startPage = ke::AlignedBase(addr, pageSize);
	void *endPage = ke::AlignedBase((void *)((intptr_t)addr + length), pageSize);
	if (mprotect(startPage, ((intptr_t)endPage - (intptr_t)startPage) + pageSize, prot) == -1) {
		ke::FormatSystemError(error, sizeof(error));
		fprintf(stderr, "mprotect: %s\n", error);
	}
#elif defined PLATFORM_WINDOWS
	DWORD old_prot;
	if (!VirtualProtect(addr, length, prot, &old_prot)) {
		ke::FormatSystemError(error, sizeof(error));
		fprintf(stderr, "VirtualProtect: %s\n", error);
	}
#endif
}

inline void SetMemPatchable(void *address, size_t size)
{
	ProtectMemory(address, (int)size, PAGE_EXECUTE_READWRITE);
}

inline void PatchRelJump32(unsigned char *target, void *callback)
{
	SetMemPatchable(target, 5);

	// jmp <32-bit displacement>
	target[0] = IA32_JMP_IMM32;
	*(int32_t *)(&target[1]) = int32_t((unsigned char *)callback - (target + 5));
}

inline void PatchAbsJump64(unsigned char *target, void *callback)
{
	int i = 0;
	SetMemPatchable(target, 14);
	
	// push <lower 32-bits>         ; allocates 64-bit stack space on x64
	// mov [rsp+4], <upper 32-bits> ; unnecessary if upper bits are 0
	// ret                          ; jump to address on stack
	target[i++] = IA32_PUSH_IMM32;
	*(int32_t *)(&target[i]) = int32_t(int64_t(callback));
	i += 4;
	if ((int64_t(callback) >> 32) != 0)
	{
		target[i++] = IA32_MOV_RM_IMM32;
		target[i++] = ia32_modrm(MOD_DISP8, 0, kREG_SIB);
		target[i++] = ia32_sib(NOSCALE, kREG_NOIDX, kREG_ESP);
		target[i++] = 0x04;
		*(int32_t *)(&target[i]) = (int64_t(callback) >> 32);
		i += 4;
	}
	target[i] = IA32_RET;
}

inline void DoGatePatch(unsigned char *target, void *callback)
{
#if defined(_WIN64) || defined(__x86_64__)
	int64_t diff = int64_t(callback) - (int64_t(target) + 5);
	int32_t upperBits = (diff >> 32);
	if (upperBits == 0 || upperBits == -1)
		PatchRelJump32(target, callback);
	else
		PatchAbsJump64(target, callback);
#else
	PatchRelJump32(target, callback);
#endif
}

inline void ApplyPatch(void *address, int offset, const patch_t *patch, patch_t *restore)
{
	unsigned char *addr = (unsigned char *)address + offset;
	SetMemPatchable(addr, patch->bytes);

	if (restore)
	{
		for (size_t i=0; i<patch->bytes; i++)
		{
			restore->patch[i] = addr[i];
		}
		restore->bytes = patch->bytes;
	}

	for (size_t i=0; i<patch->bytes; i++)
	{
		addr[i] = patch->patch[i];
	}
}

#endif //_INCLUDE_SOURCEMOD_DETOURHELPERS_H_
