Re: OK, so culicidae is *still* broken

On 2017-04-15 17:24:54 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On 2017-04-15 17:09:38 -0400, Tom Lane wrote:
> >> Why doesn't Windows' ability to map the segment into the new process
> >> before it executes take care of that?
>
> > Because of ASLR of the main executable (i.e. something like PIE).
>
> Not following. Are you saying that the main executable gets mapped into
> the process address space immediately, but shared libraries are not?

Without PIE/ASLR we can somewhat rely on pgwin32_ReserveSharedMemoryRegion
to find the space that PGSharedMemoryCreate allocated still unoccupied.
If the main binary also uses ASLR, not just libraries/stack/other
mappings, that's not guaranteed to be the case.

But this probably needs somebody with actual windows expertise
commenting.

> I wonder whether we could work around that by just destroying the created
> process and trying again if we get a collision. It'd be a tad
> inefficient, but hopefully collisions wouldn't happen often enough to be a
> big problem.

That might work, although it's obviously not pretty. We could also just
default to some out-of-the-way address for MapViewOfFileEx, that might
also work.

- Andres