hooklib: add debugger trap defuser (thanks PockyWitch!)

ferrumhook/dllmain.c

@@ -12,6 +12,7 @@
 #include "hook/process.h"
 
 #include "hooklib/serial.h"
+#include "hooklib/debug.h"
 
 #include "platform/platform.h"
 #include "gfxhook/gfx.h"
@@ -70,6 +71,8 @@ static DWORD CALLBACK ferrum_pre_startup(void)
         ExitProcess(EXIT_FAILURE);
     }
 
+    debug_hook_init();
+
     gfx_hook_init(&ferrum_hook_cfg.gfx);
     gfx_d3d11_hook_init(&ferrum_hook_cfg.gfx, ferrum_hook_mod);
     gfx_dxgi_hook_init(&ferrum_hook_cfg.gfx, ferrum_hook_mod);

hooklib/debug.c

@@ -0,0 +1,48 @@
+#include <windows.h>
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdlib.h>
+
+#include "hook/com-proxy.h"
+#include "hook/table.h"
+
+#include "hooklib/config.h"
+#include "hooklib/dll.h"
+#include "hooklib/debug.h"
+
+#include "util/dprintf.h"
+
+/* API hooks */
+
+static BOOL WINAPI hook_IsDebuggerPresent();
+
+static BOOL (WINAPI *next_IsDebuggerPresent)();
+
+/* Link pointers */
+
+static bool debug_hook_initted;
+
+static const struct hook_symbol debug_hooks[] = {
+    { .name = "IsDebuggerPresent",
+      .patch = hook_IsDebuggerPresent,
+      .link = (void **) &next_IsDebuggerPresent },
+};
+
+void debug_hook_init()
+{
+    if (debug_hook_initted) {
+        return;
+    }
+
+    debug_hook_initted = true;
+
+    hook_table_apply(NULL, "kernel32.dll", debug_hooks, _countof(debug_hooks));
+    dprintf("debug: hook enabled.\n");
+}
+
+BOOL WINAPI hook_IsDebuggerPresent()
+{
+    dprintf("debug: IsDebuggerPresent hooked.\n");
+    return false;
+}

hooklib/debug.h

@@ -0,0 +1,4 @@
+#pragma once
+#include <windows.h>
+
+void debug_hook_init();

hooklib/meson.build

@@ -9,6 +9,8 @@ hooklib_lib = static_library(
     sources : [
         'config.c',
         'config.h',
+        'debug.c',
+        'debug.h',
         'dll.c',
         'dll.h',
         'dns.c',