bug#50666: 28.0.50; Fix native compilation on Cygwin

[Achim Gratz]

Eli Zaretskii writes:
>> We still need to do something for 64-bit Cygwin.  Even though address 
>> collisions 
>> are unlikely they could still happen theoretically.  But there might be a 
>> much 
>> easier solution that doesn't necessarily require rebasing.  For example, 
>> Achim 
>> mentioned earlier the possibility of marking the eln as ASLR w/ high-entropy 
>> and
>> large address aware.
>
> Isn't that the default of the 64-bit GNU ld on Windows?  Or does
> Cygwin configure Binutils differently from MinGW?

No, I've had to remove that default since obviously it doesn't work on
Cygwin.  Yes, I have seen this problem in reality while testing the
new binutils - that why I patched it out.

> If not, we can use native-comp-driver-options, by giving it a non-nil
> value for Cygwin, to force this.

All that would be needed, on 64bit at least, is a tiny bit more control
over how ASLR works, but there isn't even proper documentation about
what it actually does (that I can find anyway).  M$ must have solved
that problem for WSL1, but whatever it was, it didn't make it to the NT
subsystem.


Regards,
Achim.
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