Theo de Raadt wrote:

> W^X is more than just stack protection. It means that all pages that
> are writeable are also marked as not executable. At least, it means
> this is how the system by default operates, until some process asks
> for something that has both write and execute permission.
>
> On some architectures W^X is easy, since the native architecture has a
> execute-permitted bit per page (sparc, sparc64, alpha, hppa, m88k).
> On other architectures, it is difficult and various hacks have to be
> done to make it work (i386, powerpc).

It's not difficult at all on x86, but having non-overlapping Segments
for Code and Data/Stack would limit the virtual address space. This
doesn't matter if your machine is equipped with 2 GB (RAM+Pagefile) or
less, because all pages of those 2 GB can completely be mapped to linear
addresses in either the code or data/stack segment. As soon as there's
more memory available, you have to decide how large the code and
data/stack segment should be.
Adressing more than 4 GB on x86 is an ugly hack anyways -PSE as well as
PAE.

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* Origin: (2:2480/8057.2)

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