Windows RT jailbreak: let the games begin
Linked by Thom Holwerda on Tue 8th Jan 2013 23:27 UTC
Windows So, a rudimentary jailbreak for Windows RT made its way onto the web these past few days. Open source applications were ported right away, and it was confirmed that Windows RT is the full Windows - it's exactly the same as regular Windows, except that it runs on ARM. Microsoft responded to the jailbreak as well.
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RE[12]: x86
by viton on Fri 11th Jan 2013 11:20 UTC in reply to "RE[11]: x86"
viton
Member since:
2005-08-09

if we can optimize the code to avoid jumps on ARM then we'll avoid the penalty.

You're doing over-engineering here. Branch elimination could be helpful, but it will work fine without it.

On ARM, there are many more registers.

ARM need more registers to implement load-op and op-in-memory x86 instructions. 16 registers is not much.

there is no need to "time share" registers, so OOO is inherently going to work differently there.
ARM OoO is much more limited, but it has 40 rename registers (on cortex-A9)

Qemu already does what your talking about.
Qemu is a full-system emulator.
x86 on WinRT should not mess with MMU pages.

This next link has the same goal, and identifies some of the same code conversion pitfalls.

The only I see here is a lack of understating of ARM arch and binary translation.

Reply Parent Score: 2

RE[13]: x86
by Alfman on Fri 11th Jan 2013 16:27 in reply to "RE[12]: x86"
Alfman Member since:
2011-01-28

viton,

"You're doing over-engineering here. Branch elimination could be helpful, but it will work fine without it."

That's because your aiming for lower branches than I am.

"ARM need more registers to implement load-op and op-in-memory x86 instructions. 16 registers is not much."

What your talking about isn't going to run as well as something optimized to use the ARM's registers natively. The x86 register limitation is a well documented bottleneck even on x86 itself where intel and amd have spent billions on making it perform well. It perplexes me why you think an ARM processor could run x86 code as well as intel can.


"Qemu is a full-system emulator. x86 on WinRT should not mess with MMU pages."

Yes, qemu manages the MMU, but even when everything is loaded into memory and running will have to incur overhead as a results of implementing x86 semantics & registers on a foreign architecture.


"The only I see here is a lack of understating of ARM arch and binary translation."

So everyone else is wrong, enlightening that.

Reply Parent Score: 2

RE[14]: x86
by viton on Fri 11th Jan 2013 23:37 in reply to "RE[13]: x86"
viton Member since:
2005-08-09

What your talking about isn't going to run as well as something optimized to use the ARM's registers natively.

The goal, to my understanding, is to execute legacy programs with competitive performance, not a Guinness records for the sake of it.

It perplexes me why you think an ARM processor could run x86 code as well as intel can.

I didn't made such a performance claims. I'm talking about good enough performance. Even if it is just 50%.

As I said, Intel engineers did ARM binary translation without any "magic buzz" about it. It just works.

Reply Parent Score: 2

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