Linux Memory Process Management on x86

Stephan Berger

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Yes.

'Des Pudels Kern - ja'.

The hardware cannot protect in smaller units than a page, as the other limiting mechanism in segments is effectively wide open.

The Copy-On-Write mechanism actually could be misused to protect smaller units than a page, but there are currently no data structures in the kernel for it. I also doubt that there will be, due to the high overhead buttociated with such mechanisms.

The C code will happily let you to shoot yourself in the foot if you properly request it. You're right about the heavy overhead buttociated with it. It could be implemented with lighter (but not zero) overhead using the segment hardware in the processor. However, it would require heavy modifications to the binary utilities (buttembler, linker & co) and program loader.

Not so complicated - the linkage vector is in the data segment of the process. The pages will be set up by the virtual memory system at first access. Remember that the Linux memory management uses demand paging. What is set up is the permission to access the pages in the mapped shared library addresses, so the page fault is a page request and not an illegal access.

The kernel is prepared to run executables in the standard layout. You'll need modifications to the process handling code and the linker scripts to make any changes - but why?

You can check the process address layout by reading some of theproc-pid-maps files (replace pid by the process number).

Maybe you should read the book

Daniel P. Bovet, Marco Cesati, Understanding the Linux Kernel, 3rd ed, O'Reilly, ISBN 0-596-00565-2.

HTH

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Tauno Voipio tauno voipio (at) iki fi