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Re: [PATCH v3 6/7] tcg: implement JIT for iOS and Apple Silicon

From: Stefan Hajnoczi
Subject: Re: [PATCH v3 6/7] tcg: implement JIT for iOS and Apple Silicon
Date: Wed, 28 Oct 2020 11:53:58 +0000

On Tue, Oct 27, 2020 at 08:07:00PM -0700, Joelle van Dyne wrote:
> On iOS, we cannot allocate RWX pages without special entitlements. As a
> workaround, we can allocate a RX region and then mirror map it to a separate
> RX region. Then we can write to one region and execute from the other one.

"separate RW region"? The sentence doesn't seem to make sense if both
regions are RX.

> When entitlements are available (macOS or jailbroken iOS), a hardware
> feature called APRR exists on newer Apple Silicon that can cheaply mark JIT
> pages as either RX or RW. Reverse engineered functions from
> libsystem_pthread.dylib are implemented to handle this.

What does "Reverse engineered functions" mean? We cannot accept code
into QEMU that is a potential liability if Apple could claim it has been
copied, derived, etc without permission. If libsystem_pthread.dylib is
open source, especially under a permissive license, then it's probably

Can you clarify?

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