Porting x86/64 Windows programs to Windows 8 ARM

Question

This article (from the Windows engineering team) says:

WOA [Windows On ARM] will not support any type of virtualization or emulation approach, and will not enable existing x86/64 applications to be ported or run.

Does that mean I won't even be able to recompile an x86/64 application from source for ARM?

If yes, what exactly prevents me from doing that? My understanding is that the Win32 API is present on Windows 8 ARM.

If no, what do they mean by not being able to port x86/64 applications to ARM?

Answer 1

From the Windows article you link to, the second quoted paragraph is the killer. Porting existing apps is definitely NOT supported.

Developers wishing to target WOA do so by writing applications for the WinRT (Windows APIs for building Metro style apps) using the new Visual Studio 11 tools in a variety of languages, including C#/VB/XAML and Jscript/ HTML5. Native code targeting WinRT is also supported using C and C++, which can be targeted across architectures and distributed through the Windows Store. WOA does not support running, emulating, or porting existing x86/64 desktop apps. Code that uses only system or OS services from WinRT can be used within an app and distributed through the Windows Store for both WOA and x86/64. Consumers obtain all software, including device drivers, through the Windows Store and Microsoft Update or Windows Update.

If we enabled the broad porting of existing code we would fail to deliver on our commitment to longer battery life, predictable performance, and especially a reliable experience over time. The conventions used by today’s Windows apps do not necessarily provide this, whether it is background processes, polling loops, timers, system hooks, startup programs, registry changes, kernel mode code, admin rights, unsigned drivers, add-ins, or a host of other common techniques. By avoiding these constructs, WOA can deliver on a new level of customer satisfaction: your WOA PC will continue to perform well over time as apps are isolated from the system and each other, and you will remain in control of what additional software is running on your behalf, all while letting the capabilities of diverse hardware shine through.

Answer 2

Only a subset of Win32 is supported on Win8 for ARM:

• http://msdn.microsoft.com/en-us/library/windows/apps/br205757.aspx

If you try to build an application that uses a Win32 API that's not supported, it won't build because the API won't be in the library. If you try to create your own library to support the APIs, the application still won't be usable because the only way to deploy apps to customers will be through the MS app store, which will no doubt check for API conformance.

From The "Building Windows for the ARM processor architecture" article:

Consumers obtain all software, including device drivers, through the Windows Store and Microsoft Update or Windows Update.

It might be possible to do so on your development machine (but maybe not - I'm really not sure if such a 'hack' will be possible, supported or not), but you certainly won't be able to deploy it in any kind of widespread fashion.

In short, any existing Win32 application will likely need significant work to be ported to Win8 for ARM. It won't be a matter of recompile and fix any errors that pop out to get the application to run on ARM.

Answer 3

They do provide this caveat a little further in your cited article:

Additionally, developers with existing code, whether in C, C++, C#, Visual Basic, or JavaScript, are free to incorporate that code into their apps, so long as it targets the WinRT API set for Windows services.

They've got version of Office and IE available; I'm positive those weren't ground-up reimplementations.