Re: cytpes and non executable memory

Bob Ippolito <bob@xxxxxxxxxx> writes:

> I don't know about windows, but mmap/msync/mprotect (or some similar
> mechanism) can and should be used to get pages that are executable.
> OpenBSD definitely doesn't have its heap marked executable on
> platforms that support it (they call this W^X, no page has both write
> and execute unless explicitly asked for).. Has anyone been testing
> there?  I bought OpenBSD 3.5 cds when I went to BSDCan, but I haven't
> installed them anywhere yet, and I won't have that kind of free time
> for at least a week.
>
> -bob

I have libffi and ctypes running on OpenBSD 3.5.  I had to hack some
preliminary code which uses mmap to allocate executable memory, and the
unittests now run without any failure.

But: mmap (or VirtualAlloc on Windows) return memory blocks with a size
rounded up to be a multiple of the system's pagesize - and it is
somewhat wasteful to use a 4k block when only 20 or 30 bytes are really
needed.  So, it seems a very simple memory manager is needed.  Since the
block size is always the same, it probably wouldn't be too complicated
to hack one, but isn't there a library I can reuse?

Thomas



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