If I'm not wrong, if an application specifies dependency in its manifest, Windows loader will load the specified version of the DLL from C:\Windows\WinSxS\xxx\ folder.
While I was researching on C:\Windows\System32\dccw.exe - which is the "Display Color Calibration" app on windows, I saw this weird behavior:
Application manifest has only one dependency - "Microsoft.Windows.Common-Controls"
which is basically the - comctl32.dll
However when you run dccw.exe, it loads two DLL from WinSXS folder; comctl32.dll as expected and also GdiPlus.dll.
Isn't a dependency for GdiPlus.dll should have been present in the manifest. Or did I not understand how WinSxS works correctly?
It is not required that all dependencies be specified in the application manifest. You can add some but leave out others.
As Hans mentioned in a comment, gdiplus under WinSxS is a hardlink to the same file in system32:
> C:\Windows\system32>fsutil.exe hardlink list GdiPlus.dll
\Windows\WinSxS\amd64_microsoft.windows.gdiplus.systemcopy_31bf3856ad364e35_10.0.
19041.1645_none_5b73408eab60fd9c\GdiPlus.dll
\Windows\System32\GdiPlus.dll
So functionally it doesn't matter which 'copy' of that file gets loaded.
As to WHY the process seems to load from WinSxS ... the two hard links are indistinguishable. There is nothing documented to suggest that WinSxS would be used as a DLL search location by default.
This may just be how Process Monitor chooses to report the file's location (?). If you compare to other tools like (archaic) Dependency Walker or Dependencies you get different results. One shows the WinSxS location, the other shows system32:
Related
We would like to ensure that when our application is loaded, it uses only Windows system DLLs and not any DLL from the folder containing the exe file for the application. The application is a standalone executable and can be run, for an example, from Download folder, hence the reason for the restriction. Unfortunately one of DLLs is not on KnownDLLs registry setting mentioned in Microsoft documentation.
The same documentation mentioned that one can use exe manifest to control the search order, but it is not clear how to do that to restrict the search path only to system libraries.
I'm writing a 32-bit C++ application on Windows 8.1 x64 using Visual Studio 2013 that depends on Python 3.3 and libVLC. I have python33.dll, libvlc.dll, and libvlccore.dll in the same directory as my executable, which I also have set as the working directory under Project > Properties > Debugging. According to MSDN, unless you're using the altered search path (which should only apply if you're using LoadLibraryEx to load the DLLs at run-time; in my case these DLLs are loaded at load-time), the application directory should always be searched before the system directory. However, according to Visual Studio, all three of these DLLs are being loaded from C:\Windows\SysWOW64. This is causing me problems as the version of libVLC I have there is much older than the one I'm trying to use.
That MSDN article only lists 3 exceptions to the normal search process. These DLLs are loaded as soon as the process starts, so obviously it couldn't be the system versions were already loaded (but just to be sure, I created a .local file since it mentioned redirection would override that, and it had no effect). I've checked the registry to see that they didn't somehow get registered as "Known DLLs", so that doesn't appear to be the problem. It's possible that python33 is being loaded as a dependency of Boost.Python, but even if it's loaded only by name the app directory should still be searched first, and in any case none of my other dependencies reference VLC. As a guess I tried marking the VLC libs as delay-load (I couldn't with Python due to data imports), and I got the following warnings, which I found interesting:
1>LINK : warning LNK4199: /DELAYLOAD:libvlc.dll ignored; no imports found from libvlc.dll
1>LINK : warning LNK4199: /DELAYLOAD:libvlccore.dll ignored; no imports found from libvlccore.dll
However, dumpbin shows that my compiled exe imports several functions from libvlc.dll.
I could of course replace or delete the system versions, but that's not really a solution if I ever attempt to distribute this application. I'm not really sure what else would be causing this. Can anyone suggest anywhere else for me to look?
Background
I'm maintaining a plugin for an application. I'm Using Visual C++ 2003.
The plugin is composed of several DLLs - there's the main DLL, that's the one that the application loads using LoadLibrary, and there are several utility DLLs that are used by the main DLL and by each other.
Dependencies generally look like this:
plugin.dll -> utilA.dll, utilB.dll
utilA.dll -> utilB.dll
utilB.dll -> utilA.dll, utilC.dll
You get the picture.
Some of the dependencies between the DLLs are load-time and some run-time.
All the DLL files are stored in the executable's directory (not a requirement, just how it works now).
The problem
There's a new requirement - running multiple instances of the plugin within the application.
The application runs each instance of a plugin in its own thread, i.e. each thread calls functions exported by plugin.dll. The plugin's code, however, is anything but thread-safe - lots of global variables etc..
Unfortunately, fixing the whole thing isn't currently an option, so I need a way to load multiple (at most 3) copies of the plugin's DLLs in the same process.
Option 1: The distinct names approach
Creating 3 copies of each DLL file, so that each file has a distinct name. e.g. plugin1.dll, plugin2.dll, plugin3.dll, utilA1.dll, utilA2.dll, utilA3.dll, utilB1.dll, etc.. The application will load plugin1.dll, plugin2.dll and plugin3.dll. The files will be in the executable's directory.
For each group of DLLs to know each other by name (so the inter-dependencies work), the names need to be known at compilation time - meaning the DLLs need to be compiled multiple times, only each time with different output file names.
Not very complicated, but I'd hate having 3 copies of the VS project files, and don't like having to compile the same files over and over.
Option 2: The side-by-side assemblies approach
Creating 3 copies of the DLL files, each group in its own directory, and defining each group as an assembly by putting an assembly manifest file in the directory, listing the plugin's DLLs.
Each DLL will have an application manifest pointing to the assembly, so that the loader finds the copies of the utility DLLs that reside in the same directory. The manifest needs to be embedded for it to be found when a DLL is loaded using LoadLibrary. I'll use mt.exe from a later VS version for the job, since VS2003 has no built-in manifest embedding support.
I've tried this approach with partial success - dependencies are found during load-time of the DLLs, but not when a DLL function is called that loads another DLL.
This seems to be the expected behavior according to this article - A DLL's activation context is only used at the DLL's load-time, and afterwards it's deactivated and the process's activation context is used.
Edit: Works with ISOLATION_AWARE_ENABLED as expected - runtime loading of DLLs uses the original activation context of the loading DLL.
Questions
Got any other options? Any quick & dirty solution will do. :-)
Will ISOLATION_AWARE_ENABLED even work with VS2003? Edit: It does.
Comments will be greatly appreciated.
Thanks!
ISOLATION_AWARE_ENABLED is implemented by the Windows SDK header files and thus probably wont worth with VS2003 at all. However, it is possible to download the latest Windows 7 SDK and use that with VS2003.
You don't need to use MT to link in manifests. Manifests can be embedded as resources in environments that dont have explicit knowledge.
Add the following to a dll's .rc file to embed a manifest. (With a recent enough platform sdk RT_MANIFEST should already be defined):
#define RT_MANIFEST 24
#define APP_MANIFEST 1
#define DLL_MANIFEST 2
DLL_MANIFEST RT_MANIFEST dllName.dll.embed.manifest
Background
My solution consists of two projects:
A standard Windows application
A DLL which my application does not use directly, but instead injects it into a target process
Basically, from my application's perspective, the only requirement that the DLL must meet is to be present in the working directory of my application. In short, my DLL doesn't export any functions that are of interest to my application.
Question
I would like to strongly couple these two binaries. What are my options aside from manually calling LoadLibrary in my application?
If this is too vague, please let me know.
Edit
Since no one seems to be "answering", I ended up doing what EFraim suggested (see comments).
I exported a dummy function from my DLL and added the DLL's generated *.lib file as an additional dependency in my application's linker property sheet. Now, at run-time, if the DLL's missing, Windows gives a nice error message and terminates execution. As an added bonus, the DLL image is also locked after successful IAT initialization; this prevents things like user deletion.
If you don't expect releasing dll and exe separately, you can add dll into your resourses and unpack it from there on startup.
I want to put my dependent files in the app directory.
I seem to remember that you can force VB6 to use the files in the local directory only.
Any hints?
You may also want to try setting up Reg-Free COM for your project. There's a freeware called Unattended Make My Manifest that will do most of the work for you.
Placing component libraries in the EXE folder (with or without .local files) can be deleterious to the hygiene of target machines too.
VB6 programs will register the components here via the self-reg entrypoint behind your back if they are not previously registered. Then if the application is moved or removed you leave the user with a broken reigistration - possibly fatal to subsequently installed applications using some of the same components. This is probably fine though for application specific components, i.e. your own DLL or OCX that will never be needed by another application.
The .local trick was really not meant for use with VB6 programs and if it is used your installer needs to be aware and properly install and register the components if they are not already on the machine. It was meant as a manual hack to get around DLL version compatibility problems on individual machines, not a deployment strategy.
Move up to SxS application and assembly manifests (Reg-Free COM and more) for a better solution. DLL/COM Redirection (.local) was a good try but it has many warts.
Clay Nichol's answer about the search order is not quite correct. That search order only applies to non-COM components. I.e. only some DLLs, and not OCXs. If you register your COM objects, they will be used from the directory where they are registered regardless of what's in the local directory, unless you use reg-free COM or a .local file.
EDIT:
MakeMyManifest is well spoken of as an automatic tool for creating manifests for VB6 projects, haven't tried it myself.
DirectCOM also has fans, again I haven't tried it.
EDIT The MMM website is down. I see here that the author was having trouble with their hosting and has provided another location to get Make My Manifest - download it here.
There is a semi-automatic technique to generate reg-free COM manifests. You can create the manifests with Visual Studio 2008 (you can use a free version like Visual Basic Express Edition). Then make a couple of edits by hand to make the manifests suitable for use from VB6. See this section of this MSDN article for step-by-step instructions - ignore the rest of the article which is about ClickOnce.
It can be sort of confusing because every version of windows, the rules change. Older versions of Windows search the path before the current directory.
A simple solution without manifests:
If your executable file is A.EXE, add a (0-byte, empty) file in the same directory named A.EXE.local -- for older versions of Windows this puts the app directory ahead of the path in the search order.
Found it myself:
Windows does look in the App Directory first:
If SafeDllSearchMode is enabled, the search order is as follows:
The directory from which the application loaded.
The system directory. Use the GetSystemDirectory function to get the path of this directory.
The 16-bit system directory. There is no function that obtains the path of this directory, but it is searched.
The Windows directory. Use the GetWindowsDirectory function to get the path of this directory.
The current directory.
The directories that are listed in the PATH environment variable. Note that this does not include the per-application path specified by the App Paths registry key. The App Paths key is not used when computing the DLL search path.
If SafeDllSearchMode is disabled, the search order is as follows:
1. The directory from which the application loaded.
2. The current directory.
3. The system directory. Use the GetSystemDirectory function to get the path of this directory.
4. The 16-bit system directory. There is no function that obtains the path of this directory, but it is searched.
5. The Windows directory. Use the GetWindowsDirectory function to get the path of this directory.
6. The directories that are listed in the PATH environment variable. Note that this does not include the per-application path specified by the App Paths registry key. The App Paths key is not used when computing the DLL search path.
according to : http://msdn.microsoft.com/en-us/library/ms682586.aspx
But you can redirect where it looks for .dll's using a Manifest:
http://msdn.microsoft.com/en-us/library/aa375365(VS.85).aspx