Re: Memory protection between compilation units?

On 2025-06-13, Mateusz Viste <mateusz@x.invalid> wrote:

On Thu, 12 Jun 2025 18:59 Kaz Kylheku wrote:

Below is a proof-of-concept program that works in GNU/Linux.  For
rapidity of prototyping, I have assumed a page size of 4096; this is
not right for all systems.

>
This is very cool! A variation of the classic "sentinel-guarded
memory" concept, where sentinels are write-protected rather than
requiring runtime checks against some magic signature.
>
Another potential strategy would be to safeguard the static array
itself, or any other data storage for that matter, immediately after the
legitimate code has finished using it. Then unprotect it only when
needed again. While this might not be a good performer for
high-frequency operations, it could be an interesting practice
for memory regions that are rarely modified.

I have taken such an approach in the integration between Valgrind
and the TXR Lisp garbage collector. Free objects are inaccessible.
During conservative parts of the scan, we could encounter, in the
run-time stack, a pointer to a freed object. So the Valgrind
API has to be used to make the object accessible before examining it.
If it is a free object, it is marked inaccessible again and ignored.

--
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca