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On macOS x86_64, the size of PAGEZERO cannot be set to 0, but it can be set to 0x1000 (4 KiB) instead of the default 4 GiB. Wine does this to support running Windows EXEs which need to load at a fixed address.

On ARM64, PAGEZERO's size cannot be made smaller than 4 GiB.

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The default 4GiB setup is done to very quickly catch poorly written / ported 32-bit code that promotes a 32-bit integer to a pointer. In 64bit mode, such a promotion will create a pointer with the top bits set to zero. Any de-reference of this sort of promotion will cause a SEGFAULT. This might happen if some sort of mixed mode compilation happened for a 64bit process where some of the code was still compiled and linked assuming 32bit mode. (mixed mode Intel code mostly)

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