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"Side By Side Assemblies" Bring DLL Hell 2.0
neutrino38 writes "This is an alert for all developers using Microsoft Visual Studio 2005. At the beginning of January, Microsoft issued a security fix for Visual Studio 2005 forcing the use of new dynamic libraries (DLLs) by all applications compiled with this IDE. Basically, applications compiled with Visual Studio 2005 will not work anymore on an ordinary (non-dev) PC unless the newer DLLs are installed. And we found out that this is true on fully updated PCs. I just posted some details and some suggested fixes." Read below for some more background on Microsoft's so-called "side by side assemblies."
For those unfamiliar with the Microsoft world, native microsoft applications written in C++ rely on dynamic libraries. Two of them are infamous: MSVCRT.DLL and MFCxx.dll. Because of software evolution and security fixes, multiple versions of these DLLs were often present in the system, causing application instability. Where Linux implemented a simple suffix notation on the dynamic libraries, Microsoft created a new beast in 2001: the Side By Side assembly. These are basically DLLs with a companion XML file that identifies them. The XML file contains a digital signature and when the system binds these DLLs dynamically to an application, it checks that the signature of the DLL matches the DLL itself. When everythings runs well, this is pretty transparent. But when issues arise, it becomes excruciatingly difficult to troubleshoot and fix. DLL hell is not over.
For those unfamiliar with the Microsoft world, native microsoft applications written in C++ rely on dynamic libraries. Two of them are infamous: MSVCRT.DLL and MFCxx.dll. Because of software evolution and security fixes, multiple versions of these DLLs were often present in the system, causing application instability. Where Linux implemented a simple suffix notation on the dynamic libraries, Microsoft created a new beast in 2001: the Side By Side assembly. These are basically DLLs with a companion XML file that identifies them. The XML file contains a digital signature and when the system binds these DLLs dynamically to an application, it checks that the signature of the DLL matches the DLL itself. When everythings runs well, this is pretty transparent. But when issues arise, it becomes excruciatingly difficult to troubleshoot and fix. DLL hell is not over.
What might be interesting to note here is that the summary isn't everything there is to side-by-side (SxS) assemblies.
Suppose you're building an application using two DLLs, let's call them A and B. Both depend on a third DLL named C. Now, suppose A uses C version X, and B uses C version Y. You're screwed, right? Not with SxS, since that allows multiple versions of C to be loaded. That's the real added value of SxS.
All this is in theory of course, which as we all know is in theory equal to practice, but in practice is not...
Error: password can't contain reverse spelling of ancient Chinese emperor
That defeats the whole purpose of a DLL anyway. The thought was that you wouldn't have to "reinvent the wheel" and you could reuse code. However, Microsoft's failure to document their operating system's API thoroughly in a public manner led to developers relying on undocumented features that were later changed. Then, those applications needed older versions of those libraries and would install them over the newer versions. This, of course, crashed the newer applications. Ugh.
That's great until some common library needs to be updated for a security hole, and you have download 20 updates from different vendors (assuming they even provide updates...) rather than 1 item in Windows Update.
Everyone (even Windows programmers) should read Ulrich Drepper's piece on how to write shared libraries. (Warning: PDF.) (Likewise, even free software developers should read Raymond Chen's blog.)
Oh jesus christ I can't stand how fucking idiotic everything in this discussion is.
What happened: In August, they released a patch to the IDE that required a new version of the shared libraries. Binaries built with this patched version of the IDE/compiler/toolchain will by default require a version of DLLs that aren't installed by default on many systems.
What would have prevented this asshat's blog post: Write a fucking installer that includes the DLLs you use. Thus, when your compiler changes, and your new packages rely on some stuff, magically that 'some stuff' is bundled along with your binary, and everything _still works_. Relying on OTHER packages to have good installers that properly put stuff in to SxS is just idiotic. "Wah, I rely on stuff that I'm specifically told I can't rely on, Microsoft sucks, and SxS is evil!"
No. SxS has been SAVING your ass from updates like this since Windows XP. Surprisingly, you can now NOT recompile your project, and have it still work, even though there's a newer version of DLLs you depend on, because the backwards compatibility problem of these DLLs is just gone. The version YOU want and need and depend on is still there, still usable. Something else on the system that wants the newer version gets it, and all its patched glory. This is actually a security hole, and in THAT case, the DLL you depend on WILL change to fix the security problem. Nothing in the August 2009 update to VS 2005 seems to indicate that this happened, it's only for newly compiled binaries.
So, in summary: The blog poster is an idiot, he hates his user, he's too lazy to write a real installer, he has incompetent developers that don't care about the security of their product, and he asked for help and got 4 completely idiotic responses. Now everyone on slashdot who knows nothing about SxS and the actual problems it causes (and yes there are some) think that it's the same problem we've always had, but worse.
Note: I'm not a Windows developer (Linux developer), and I've not used Windows in well over a year (Mac user). But I've been bitten by SxS in my last job and dealing with VB.Net, back when I didn't know I had to make a real installer for my stuff. I somehow managed to learn to not be an idiot, and the blog poster should too.
Additionally, DLLs can enhance security. If there's a bug in MSVCRT.DLL, Microsoft can patch it and release it as an update. In a static world, every application that had that buggy code compiled into it would have to be rebuilt and redistributed.
In a statically-linked world, every application would need to be rebuilt (on Windows, redistributed) every time an API / ABI change was released, as well as every time a bug was fixed. Furthermore, download sites would either have to release binaries for every API / ABI combination (that's a ton of releases per version) and deal with users downloading the wrong one, or do the open-source model and release the source, forcing the users to build the application on their system and rebuild every API / ABI update. And somehow I don't think the latter solution would fly with the Windows community.
Like other posters have said, Microsoft's solution is actually not a bad one. Allowing multiple DLLs to be loaded simultaneously is not a pretty solution, but it's not a pretty problem that they have to solve, either. Advance with backwards-compatibility in mind as much as it makes sense to, and use SxS DLLs when it doesn't.
Oops. Correct link. (I wish Slashdot would warn about obviously incorrect links.)
That said, I thought that OS X apps were statically linked (except with OS libs), and thus tend to be large, but reduce this issue since so much functionality is based on system libs. I could be wrong.
Yeah, you are wrong. Mac OS X apps are definitely dynamically linked (the equivalent of so on Mac OS X is dylib). The reason Mac OS X apps can be larger than executables on other platforms is because they often contain machine code for multiple platforms (ppc, x86, x86_64). That only translates to a large footprint in storage.
Now you know.
This author takes full ownership and responsibility for the unpopular opinions outlined above.
But when issues arise, it becomes excruciatingly difficult to troubleshoot and fix.
The version information is written in plain text in the manifest. The files have names based on the version information in the WinSxS folder. If you get the error and notice the files aren't there, its fairly trivial to troubleshoot and fix.
I'm not a fan of side by side assemblies, I just hate to see issues like this blown out of proportion as it obscures some of the real issues that developers face when developing for Windows (such as just about every bug filed on Microsoft Connect being closed as "by design" instead of being worked on or at the very least closed as "can't fix, compatibility issues", for example).
You are 100% correct. The "problem" with those guys is that they did not even understand that they have to redistribute CRT DLL with their binaries even before the update. They got lucky there because on most systems, it is already there (I believe Vista has it out of the box, and probably some MS software will install it on XP - maybe even IE7/8?), so they got away with not distributing it. Now the update brought in a newer version of runtime, which of course the clients don't have, and they suddenly realize that they didn't distribute their dependencies properly. What does "DLL Hell" or side by side assemblies even have to do with it?
And, if they find it so hard to comprehend the idea that they have to give users the DLLs they link against, they could always just compile CRT statically and be done with it.
Hands up anyone who knows what an "activation context" is! If you don't you have no idea what WinSxS does, how it does it or how to diagnose it when it goes wrong.
In my opinion, WinSxS is a good mechanism, or at least as good as Microsoft could have made it while working within the constraints of history. However, WinSxS cannot be used in the real world without properly understanding it, and achieving that understanding is very painful indeed. The MSDN documentation is piecemeal, appears incomplete and inaccurate in a few places and lacks a proper overview. I think the only reason I properly twigged what activation contexts are about is that I had recently written a mechanism that operated on similar principles (a thread-local stack of context-related information).
I wrote a Wiki page at work describing what (I think) WinSxS's motivation is, how it works and some of the problems it suffers from. I'd like to put it somewhere on the public internet - any suggestions? It should ideally be somewhere wiki-like where people can correct its inevitable inaccuracies without me having to maintain it, but I'm not sure it's appropriate for wikipedia.
"The Milliard Gargantubrain? A mere abacus - mention it not."