plugin_child_interpose.mm

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

// Use "dyld interposing" to hook methods imported from other libraries in the
// plugin child process.  The basic technique is described at
// http://books.google.com/books?id=K8vUkpOXhN4C&pg=PA73&lpg=PA73&dq=__interpose&source=bl&ots=OJnnXZYpZC&sig=o7I3lXvoduUi13SrPfOON7o3do4&hl=en&ei=AoehS9brCYGQNrvsmeUM&sa=X&oi=book_result&ct=result&resnum=6&ved=0CBsQ6AEwBQ#v=onepage&q=__interpose&f=false.
// The idea of doing it for the plugin child process comes from Chromium code,
// particularly from plugin_carbon_interpose_mac.cc
// (http://codesearch.google.com/codesearch/p?hl=en#OAMlx_jo-ck/src/chrome/browser/plugin_carbon_interpose_mac.cc&q=nscursor&exact_package=chromium&d=1&l=168)
// and from PluginProcessHost::Init() in plugin_process_host.cc
// (http://codesearch.google.com/codesearch/p?hl=en#OAMlx_jo-ck/src/content/browser/plugin_process_host.cc&q=nscursor&exact_package=chromium&d=1&l=222).

// These hooks are needed to make certain OS calls work from the child process
// (a background process) that would normally only work when called in the
// parent process (the foreground process).  They allow us to serialize
// information from the child process to the parent process, so that the same
// (or equivalent) calls can be made from the parent process.

// This file lives in a seperate module (libplugin_child_interpose.dylib),
// which will get loaded by the OS before any other modules when the plugin
// child process is launched (from GeckoChildProcessHost::
// PerformAsyncLaunch()).  For this reason it shouldn't link in other
// browser modules when loaded.  Instead it should use dlsym() to load
// pointers to the methods it wants to call in other modules.

#if !defined(__LP64__)

#  include <dlfcn.h>
#  import <Carbon/Carbon.h>

// The header file QuickdrawAPI.h is missing on OS X 10.7 and up (though the
// QuickDraw APIs defined in it are still present) -- so we need to supply the
// relevant parts of its contents here.  It's likely that Apple will eventually
// remove the APIs themselves (probably in OS X 10.8), so we need to make them
// weak imports, and test for their presence before using them.
#  if !defined(__QUICKDRAWAPI__)

struct Cursor;
extern "C" void SetCursor(const Cursor* crsr) __attribute__((weak_import));

#  endif /* __QUICKDRAWAPI__ */

BOOL (*OnSetThemeCursorPtr)(ThemeCursor) = NULL;
BOOL (*OnSetCursorPtr)(const Cursor*) = NULL;
BOOL (*OnHideCursorPtr)() = NULL;
BOOL (*OnShowCursorPtr)() = NULL;

static BOOL loadXULPtrs() {
  if (!OnSetThemeCursorPtr) {
    // mac_plugin_interposing_child_OnSetThemeCursor(ThemeCursor cursor) is in
    // PluginInterposeOSX.mm
    OnSetThemeCursorPtr =
        (BOOL(*)(ThemeCursor))dlsym(RTLD_DEFAULT, "mac_plugin_interposing_child_OnSetThemeCursor");
  }
  if (!OnSetCursorPtr) {
    // mac_plugin_interposing_child_OnSetCursor(const Cursor* cursor) is in
    // PluginInterposeOSX.mm
    OnSetCursorPtr =
        (BOOL(*)(const Cursor*))dlsym(RTLD_DEFAULT, "mac_plugin_interposing_child_OnSetCursor");
  }
  if (!OnHideCursorPtr) {
    // mac_plugin_interposing_child_OnHideCursor() is in PluginInterposeOSX.mm
    OnHideCursorPtr = (BOOL(*)())dlsym(RTLD_DEFAULT, "mac_plugin_interposing_child_OnHideCursor");
  }
  if (!OnShowCursorPtr) {
    // mac_plugin_interposing_child_OnShowCursor() is in PluginInterposeOSX.mm
    OnShowCursorPtr = (BOOL(*)())dlsym(RTLD_DEFAULT, "mac_plugin_interposing_child_OnShowCursor");
  }
  return (OnSetCursorPtr && OnSetThemeCursorPtr && OnHideCursorPtr && OnShowCursorPtr);
}

static OSStatus MacPluginChildSetThemeCursor(ThemeCursor cursor) {
  if (loadXULPtrs()) {
    OnSetThemeCursorPtr(cursor);
  }
  return ::SetThemeCursor(cursor);
}

static void MacPluginChildSetCursor(const Cursor* cursor) {
  if (::SetCursor) {
    if (loadXULPtrs()) {
      OnSetCursorPtr(cursor);
    }
    ::SetCursor(cursor);
  }
}

static CGError MacPluginChildCGDisplayHideCursor(CGDirectDisplayID display) {
  if (loadXULPtrs()) {
    OnHideCursorPtr();
  }
  return ::CGDisplayHideCursor(display);
}

static CGError MacPluginChildCGDisplayShowCursor(CGDirectDisplayID display) {
  if (loadXULPtrs()) {
    OnShowCursorPtr();
  }
  return ::CGDisplayShowCursor(display);
}

#  pragma mark -

struct interpose_substitution {
  const void* replacement;
  const void* original;
};

#  define INTERPOSE_FUNCTION(function)                         \
    {                                                          \
      reinterpret_cast<const void*>(MacPluginChild##function), \
          reinterpret_cast<const void*>(function)              \
    }

__attribute__((used)) static const interpose_substitution substitutions[]
    __attribute__((section("__DATA, __interpose"))) = {
        INTERPOSE_FUNCTION(SetThemeCursor),
        INTERPOSE_FUNCTION(CGDisplayHideCursor),
        INTERPOSE_FUNCTION(CGDisplayShowCursor),
        // SetCursor() and other QuickDraw APIs will probably be removed in OS X
        // 10.8.  But this will make 'SetCursor' NULL, which will just stop the OS
        // from interposing it (tested using an INTERPOSE_FUNCTION_BROKEN macro
        // that just sets the second address of each tuple to NULL).
        INTERPOSE_FUNCTION(SetCursor),
};

#endif  // !__LP64__