Windows: Current State of Support

Related to the recent post Why is the OpenDylan IDE only on Windows?, another source of common questions are some of the requirements that we have for running on Windows and the state of 64 bit Windows support.

Building Open Dylan Applications on Windows

Building an Open Dylan application on any platform requires at least a linker. On Windows, it also requires a resource compiler for handling .rc files which controls things like an applications icons.

On Windows, we support debugging an application written in Dylan when using the Open Dylan IDE. To do this, we must have the debug data available. Our debug data on Windows is in CodeView 4 (CV4) format rather than the more modern PDBs in use today. This is partially a historical artifact of the fact that this code was written in the 1990s and partially due to the later formats not being publicly specified.

So, to link on Windows and support debugging, we need a linker that supports CV4 debug data. Unfortunately, Microsoft removed support for this in their linkers after Visual C 6. However, the PellesC linker, polink does support CV4 debug data.

PellesC also provides a resource compiler, porc.exe.

PellesC provides a complete toolchain that allows for Dylan applications to be linked and debugged. Using more recent versions of Visual Studio may allow linking a Dylan application, but it will not work with the debugger. Using Visual C 6 is possible, but it is no longer available and requires using a Windows SDK from 2003 as more recent ones don't work with Visual C 6.

Hopefully it is clear that the easiest thing to do currently is to use the PellesC toolchain for linking and debugging Dylan applications on Windows.

In the future, we hope to integrate aspects of the PellesC distribution into our installer to make this a seamless and easy installation.

Building Open Dylan on Windows

Much of this is the same as the above, except that we currently have to use Visual C 6 for a full bootstrap rather than PellesC.

The issue at play here is that the low-level runtime code includes the excellent MPS garbage collector from Ravenbrook. There is some code within MPS that triggers a bug in PellesC. We are also using a slightly older version of MPS as the current version triggers a different set of bugs in Visual C 6 due to MPS having support for 64 bit Windows.

We are working on producing a minimized test case of the issues with compiling MPS with PellesC so that we can eventually use PellesC to build a full bootstrap of the Open Dylan IDE. This will also allow us to upgrade to the current versions of MPS which are faster and more stable.

Running the Open Dylan IDE on 64-bit Windows

The Open Dylan IDE does not run on 64-bit Windows prior to Windows 8. This is due to a bug in a low level portion of Windows known as "WoW64" which had a bug in an API call GetThreadContext. This breaks many garbage collectors when trying to run a 32-bit application on 64-bit Windows while using threads. Our IDE uses threads and, since it is built for 32-bit Windows, has fallen victim to this issue.

However, the command line tools do not use threads and are able to run on 64-bit Windows.

We do not currently support producing a 64-bit build of Open Dylan on Windows because we use a compiler backend on Windows that produces native code. Our 64-bit platform support comes from using a compiler backend that generates C, but that backend doesn't support Windows. This situation will hopefully improve with the upcoming LLVM compiler backend which will make it easier for us to generate 64-bit Windows code, although we will then have some exciting problems to solve surrounding debugging.

Hopefully this helps clarify the current status and where we're going in the future!