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/*
* Copyright © Hayden K <imaciidz@gmail.com>
* Copyright © Willian Henrique <wsimanbrazil@yahoo.com.br>
* Copyright © Michael Smith <mikesmiffy128@gmail.com>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
* OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
* PERFORMANCE OF THIS SOFTWARE.
*/
#include "accessor.h"
#include "asm.h"
#include "chunklets/x86.h"
#include "con_.h"
#include "errmsg.h"
#include "feature.h"
#include "gametype.h"
#include "hook.h"
#include "intdefs.h"
#include "mem.h"
#include "sst.h"
#include "vcall.h"
#include "x86util.h"
FEATURE("Left 4 Dead 1 demo file backwards compatibility")
GAMESPECIFIC(L4D1_1022plus)
struct CDemoFile;
// NOTE: not bothering to put this in gamedata since it's actually a constant.
// We could optimise the gamedata system further to constant-fold things with no
// leaves beyond the GAMESPECIFIC cutoff or whatever. But that sounds annoying.
#define off_CDemoFile_protocol 272
DEF_ACCESSORS(struct CDemoFile, int, CDemoFile_protocol)
// L4D1 bumps the demo protocol version with every update to the game, which
// means whenever there is a security update, you cannot watch old demos. From
// minimal testing, it seems demos recorded on version 1022 and onwards are
// compatible with the latest version of the game, so this code lets us watch
// 1022+ demos on any later version of the game.
typedef int (*GetHostVersion_func)();
DEF_INLINE_HOOK_NOTRAMPOLINE(GetHostVersion_func, GetHostVersion)
typedef void (*VCALLCONV ReadDemoHeader_func)(struct CDemoFile *);
DEF_INLINE_HOOK(ReadDemoHeader_func, ReadDemoHeader)
int _l4d1democompat_demover; // extern for asm
static int gameversion;
static int hookdest_GetHostVersion() {
// If the demo version is 1022 or later, and not newer than the version we
// are currently using, then we spoof the game version to let the demo play.
if (_l4d1democompat_demover >= 1022 &&
_l4d1democompat_demover <= gameversion) {
return _l4d1democompat_demover;
}
return gameversion;
}
int *_l4d1democompat_thisproto; // extern for asm
static void VCALLCONV hookdest_ReadDemoHeader(struct CDemoFile *this) {
// The mid-function hook needs to get the protocol from `this`, but by that
// point we won't be able to rely on the ECX register and/or any particular
// stack spill layout. So... offset the pointer and stick it in a global.
_l4d1democompat_thisproto = getptr_CDemoFile_protocol(this);
orig_ReadDemoHeader(this);
}
// should this be in its own .S file? meh, leaving it here for now.
__asm (
".pushsection " ASM_RWX_SECTION_STR ", \"" ASM_RWX_SECTION_FLAGS "\"\n"
".globl " ASM_MANGLE_STR("_l4d1democompat_midpoint_hook") "\n"
ASM_MANGLE_STR("_l4d1democompat_midpoint_hook") ":\n"
// like in con_.S, we have to assemble stuff manually here, annoyingly.
// note: ebx is safe to clobber here because we're hooking immediately after
// a call, ebx is caller-save, and also ebx is explicitly pushed before the
// call which means we know the code we're hooking obeys the calling conv.
// see also find_midpoint() below.
// mov ebx, [_l4d1democompat_thisproto]
".byte 0x8B\n"
".byte 0x1D\n"
".long " ASM_MANGLE_STR("_l4d1democompat_thisproto") "\n"
// mov ebx, [ebx]
".byte 0x8B\n"
".byte 0x1B\n"
// mov [_l4d1democompat_demover], ebx
".byte 0x89\n"
".byte 0x1D\n"
".long " ASM_MANGLE_STR("_l4d1democompat_demover") "\n"
// and then we leave trampoline space immediately after; we can jump
// straight back from here to the rest of the function!
".globl " ASM_MANGLE_STR("_l4d1democompat_midpoint_trampoline") "\n"
ASM_MANGLE_STR("_l4d1democompat_midpoint_trampoline") ":\n"
".space 24\n"
".popsection\n"
);
// XXX: dummy function prototype. not to be called directly, just to pass into
// the inline hooking machinery.
// maybe one day we'll come up with a marginally cleaner way of doing these
// midpoint hooks, although there's not many uses currently so no big deal.
int _l4d1democompat_midpoint_hook();
int _l4d1democompat_midpoint_trampoline();
DEF_INLINE_HOOK_WITHTRAMPOLINE(int (*)(), ReadDemoHeader_midpoint,
_l4d1democompat_midpoint_trampoline)
static inline ReadDemoHeader_func find_ReadDemoHeader(const uchar *insns) {
// Find the call to ReadDemoHeader in the listdemo callback
for (const uchar *p = insns; p - insns < 192;) {
if (p[0] == X86_LEA && p[1] == X86_MODRM(2, 1, 4) && p[2] == 0x24 &&
p[7] == X86_CALL && p[12] == X86_LEA &&
p[13] == X86_MODRM(2, 1, 4) && p[14] == 0x24) {
return (ReadDemoHeader_func)(p + 12 + mem_loads32(p + 8));
}
NEXT_INSN(p, "ReadDemoHeader");
}
return 0;
}
static inline void *find_midpoint(ReadDemoHeader_func ReadDemoHeader) {
uchar *insns = (uchar *)ReadDemoHeader;
for (uchar *p = insns; p - insns < 128;) {
const u64 HL2DEMO = 0x4F4D4544324C48; // "HL2DEMO\0" ascii, little-endian
if (p[0] == X86_PUSHIW && p[5] == X86_PUSHEBX && p[6] == X86_CALL &&
!mem_loadu64(mem_loadptr(p + 1)) == HL2DEMO) {
return p + 11;
}
NEXT_INSN(p, "ReadDemoHeader hook midpoint");
}
return 0;
}
static inline GetHostVersion_func find_GetHostVersion(
ReadDemoHeader_func ReadDemoHeader) {
uchar *insns = (uchar *)ReadDemoHeader;
int jzcnt = 0;
for (uchar *p = insns; p - insns < 192;) {
// GetHostVersion() is called right after the third JZ insn in
// ReadDemoHeader()
if (p[0] == X86_JZ && ++jzcnt == 3) {
return (GetHostVersion_func)(p + 7 + mem_loads32(p + 3));
}
NEXT_INSN(p, "GetHostVersion");
}
return 0;
}
INIT {
struct con_cmd *cmd_listdemo = con_findcmd("listdemo");
if_cold (!cmd_listdemo) return FEAT_INCOMPAT; // should never happen!
ReadDemoHeader_func ReadDemoHeader = find_ReadDemoHeader(
cmd_listdemo->cb_insns);
if_cold (!ReadDemoHeader) {
errmsg_errorx("couldn't find ReadDemoHeader function");
return FEAT_INCOMPAT;
}
void *midpoint = find_midpoint(ReadDemoHeader);
if_cold (!midpoint) {
errmsg_errorx("couldn't find mid-point for ReadDemoHeader hook");
return FEAT_INCOMPAT;
}
GetHostVersion_func GetHostVersion = find_GetHostVersion(ReadDemoHeader);
if_cold (!GetHostVersion) {
errmsg_errorx("couldn't find GetHostVersion function");
return FEAT_INCOMPAT;
}
gameversion = GetHostVersion();
int err = hook_featsetup_GetHostVersion(GetHostVersion);
if_cold (err) return err;
struct hook_featsetup_ret_ReadDemoHeader h2 =
hook_featsetup_ReadDemoHeader(ReadDemoHeader);
if_cold (h2.err) return h2.err;
struct hook_featsetup_ret_ReadDemoHeader_midpoint h3 =
hook_featsetup_ReadDemoHeader_midpoint((int (*)())midpoint);
if_cold (h3.err) return h3.err;
hook_commit_GetHostVersion(&hookdest_GetHostVersion);
hook_commit_ReadDemoHeader(h2.hookpos, &hookdest_ReadDemoHeader);
hook_commit_ReadDemoHeader_midpoint(h3.hookpos,
&_l4d1democompat_midpoint_hook);
return FEAT_OK;
}
END {
if_cold (sst_userunloaded) {
unhook_ReadDemoHeader_midpoint();
unhook_ReadDemoHeader();
unhook_GetHostVersion();
}
}
// vi: sw=4 ts=4 noet tw=80 cc=80
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