[Q] Windows 8 on ARM

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As this is a developers forum - lets share here information on WoA (Windows on ARM) architecture.

What is known for now from different sources:
- WoA 8 would require UEFI to boot (instead of BIOS on x86), ACPI is required too. So no WoA to existing devices (they don't have UEFI/ACPI and I don't think that anyone would waste his time on emulating them).
- No native support for x86 apps on ARM, nor ARM apps on x86. Only .NET apps would work in both worlds.
But it is possible to create an emulator similar to DosBox that would run native x86 programs on WoA and, for example, I'm currently working in this direction.
- Though existing C++ apps can be recompiled for ARM from sources, it is not a 100% working solution. Current VS11 contains a rather limited set of ARM libraries - no DirectX libs earlier than 11, no import libraries for NtDll.Dll and similar DLLs.
I don't have access to any WoA builds, so I can't check whether these features are completely removed from ARM, or those LIBs are just not present in current VS11 build. But at least now we can compile test apps for ARM and analyze the code (though we don't have where to execute them yet).
- Native WoA programs use THUMB2 instruction set (ARMv7 and above). Though ARM instruction set would be supported too.
- According to "Microsoft Portable Executable and Common Object File Format Specification v8.2" WoA machine type in PE files would be 0x1c4, and some new relocations types are added (for example IMAGE_REL_BASED_ARM_MOV32T = 7). IDA understands such EXE files, though complains on relocs.
- SEH is implemented in a different way than on x86 (similar to x64, google for RtlAddFunctionTable to get the idea).
- WoA is more secure by default. For example TPM can be rarely found on x86, but it would be required on ARM.
- Most of existing drivers are source-code compatible with ARM (of cause if not using x86-specific stuff). But ARM would never allow to load unsigned drivers (unlike x86 Win7/8).
- As platform is completely new - all ARM drivers would be added to windows update site to simplify our life. Some obsolete hardware like 1394 is not implemented at all, so there would not be so many drivers for ARM llike for x86.
- All binaries would be the same for all SoC providers.
- No "native" ARM VisualStudio - developer tools are x86 only.

WoA requirements from different sources:
- 10.1” display with 1366x768 min resolution (though smaller screens may be supported with reduced functionality)
- Volume Control, Windows, Rotation, Lock power buttons
- Dual core CPU with hardware accelerated GPU
- at least 1 Gb RAM
- min 16 Gb fixed storage
- 100mW idle power in standby
- there are rumors that there would be standart "Phone call API" ("Apollo" UI)

Does anyone have access to ARM WDK? It would definitely contain a complete set of import libraries and would provide lots of info on WoA internals in headers/documentation. Seems that Windows 8 WDK on MSDN does not have ARM tools

so your bottom line says: no w8 on arm (ever)?

I'm not quite sure where you found that it requires ACPI. I didn't turn anything up.
The UEFI requirement is expected, and I doubt will be that much of a hurdle. UEFI is all open, and it should be pretty trivial to chainload a UEFI-compatible environment on top of the existing firmwares, provided that nvidia doesn't provide us with an implementation to start with, which I suspect they'll do.

For the emulator, I believe the best thing to do would be to provide something opposite of WINE, something that'd emulate the instructions, but pass API calls and translate between the two. A full Windows SDK will likely come out for ARM processors once it's finalized, if it's not already out. Have you checked in the Ultimate build of VS2011, or the express build?

Everything I could find relating to the TPM says that it's optional, but will be automatically utilized if available.

The rest is pretty inconsequental, at least to what I think most people here are interested in.


nvidia started a windows 8 development program for ARM (Clickey here), but I haven't seen anything else from it, has anyone else gotten anything?

Originally Posted by mamaich

As this is a developers forum - lets share here information on WoA (Windows on ARM) architecture.

What is known for now from different sources:
- WoA 8 would require UEFI to boot (instead of BIOS on x86), ACPI is required too. So no WoA to existing devices (they don't have UEFI/ACPI and I don't think that anyone would waste his time on emulating them).

Actually they said it would continue to support BIOS for older devices.

See: Current machines dual-booting Windows 7 and Linux should be able to upgrade to Windows 8 without wiping out the Linux install. As Microsoft notes in the Building Windows 8 blog, “We will continue to support the legacy BIOS interface.” However, machines using UEFI instead of BIOS “will have significantly richer capabilities” including faster boot times and greater security. (from Arstechnica)

That's for x86. ARM was said to require UEFI. Besides, there is no real bios on Android tablets, at least not a common platform.

Originally Posted by netham45

I'm not quite sure where you found that it requires ACPI. I didn't turn anything up.

I've got it in one of the "windows-on-arm" non-public documents dated the first half of this year. While UEFI,ACPI,TPM are an option for x86, they are required for ARM hosts.
So no custom WM8 bootloaders, drivers, patched kernel on ARM hosts (like "windows activators" do) until sign keys would be leaked or some backdoors would be found. Of cause this is good as this would make rootkit creation more difficult, and require device drivers signed by MS (so we'd get more stable OS) but I really don't think that this "protection" would last more than 1-2 months after WoA would be released.

For the emulator, I believe the best thing to do would be to provide something opposite of WINE, something that'd emulate the instructions, but pass API calls and translate between the two.

I'm already working on such tool. It emulates x86 instruction set with dosbox or bochs CPU emulation library (I'm using both of them for debugging purposes, while working on my own one that would be much more simple->faster), translates x86 WinAPI to "native" host WinAPI + emulates API that is not present or differently implemented on WoA. It is designed to be truly cross-platform, so just a recompilation + creating several thunks/stubs would be necessary when I'll get my hands to an ARM host running windows8.
Of cause programs that use heavy anti-debugging, self-modifying code, undocumented features and SEH tricks would not work. Currently it is rather far from being finished (I have to implement&debug WinAPI and COM thunks that cannot be automatically generated) but old games like "heroes of might and magic" are already working fine in a test environment.

A full Windows SDK will likely come out for ARM processors once it's finalized, if it's not already out. Have you checked in the Ultimate build of VS2011, or the express build?

Of cause I'm talking about "ultimate" VS11, as express is designed to target mostly .NET (though ARM compiler is present there too).
And WDK that it published on MSDN does not allow creation of ARM drivers. I'm currently in a process of renewing my company's MSDN subscription, so I can't prove that myself, but I've read that on OSR forums.

I am waiting to hack my iPad and put win8 on it

I would hope touchpad would be the next viable option. Hp could still make more and just dump W8 on it. Thanks all of you for working this thread. I will be reading your progress as it unfolds. Good Luck devs and if I can find anything you will be the first to know.

Sent from my mwp6985 / Trophy using XDA Windows Phone 7 App

Some information on Win8 "Apollo" is available. Apollo - is a name for a new "windows phone" OS from MS.
- Apollo is based on the same "desktop" code as Windows 8. No Windows CE at last!
- Apollo would provide the same user experience as old Windows Phone 7.x - Metro UI, People hub, builtin office apps, etc. Seems that software compatibility with WinPhone 7.x apps would be preserved, but this is just my own guess.
- All applications on Apollo are required to be signed, similar to Windows Phone 7.
- Device drivers can be written only by IHVs, MS and OEMs, not by ISVs. This would be a problem for antivirus vendors or tools like daemon-tools.
- There would be a "built-in" eMMC card with OS and vendor partitions, and maximum one SD card. eMMC supports NTFS, SD-card supports only FAT/exFAT.
Build-in eMMC would have C:\ drive letter, SD-card would be D:\ if present.
eMMC contains several partitions. Some of them would be made readonly during boot.
- Near Field Communication is built in.
- The same list of sensors as in WP7 Mango is supported.
- There would be BSOD like in a desktop OS
- Unproven, but it seems that only .NET ("Splash UI framework" and "Silverlight") APIs would be available to independent developers. So no native code again.
- Seems that x86 architecture is supported for Apollo too.