[PATCH 0/4] macOS/arm64 support

[Stefan Dösinger]

> - Setting -pagezero_size to anything less than 4 GB seems to make
>  macOS refuse to run the executable. So this makes it impossible to
>  map anything into the lower 4 GB of the address space. For now,
>  I've worked it around by moving the address at which user_shared_data
>  is allocated.

Shouldn't you be able to forcefully remap parts in the zero page? To my knowledge the only thing you can't do is unmap pages that the dynamic loader thinks are allocated - if it gets them again when loading a different .dylib it will crash and burn. But you can map stuff there with MAP_FIXED yourself as long as you can be sure you don't overwrite anything important - which shouldn't be the case in the zero page.

> - Memory mappings can't be writable and executable at the same time.
>  If one mmap()s a page and request it to be both writable and
>  executable, writing to it fails, same if changing protection with
>  mprotect().

In Catalina you can bypass that with the right protected runtime entitlements. That means you'll have to sign your executable with a manifest that enables the protected runtime and requests the entitlements. Do you know if this still works in Big Sur x86_64 and/or big sur ARM?
> 
> - Darwin also treats x18 as reserved, just like windows, but IIRC
>  the system can spuriously(?) overwrite the register to zero at
>  some times. I haven't run into this in the context of wine on macOS
>  yet though.

Yeah someone warned me that this happens on iOS. The Darwin kernel code should be accessible I think. Any way to find out under which conditions this happens?


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