[OSy] Details on inaccessible memory blocks in process address space

[Petr Tůma]

Hi,

during yesterday's lecture, one of the topics that came up was the reason for the existence of inaccessible 
memory blocks in process address space, that is, the blocks labeled with "---p" in "/proc/*/maps". In case you 
want to know more (who doesn't :-), here are some explanations on selected use cases:

- Use to connect otherwise discontinuous segments, and to reserve heap space without allocation - 
https://unix.stackexchange.com/questions/353676/what-is-the-purpose-of-seemingly-unusable-memory-mappings-in-linux/353685#353685

- Safepoint implementation in virtual machines - http://psy-lob-saw.blogspot.com/2015/12/safepoints.html, 
https://psy-lob-saw.blogspot.com/2014/03/where-is-my-safepoint.html

- Stack guard page - https://lwn.net/Articles/725832/, 
https://www.qualys.com/2017/06/19/stack-clash/stack-clash.txt

- Or maybe just guard pages in general - 
https://docs.microsoft.com/en-us/windows/desktop/memory/creating-guard-pages

Happy reading :)

Petr

-- 
Petr Tuma
Distributed and Dependable Systems
Faculty of Mathematics and Physics
Charles University, Czech Republic
       http://d3s.mff.cuni.cz