Self-modifying code: Difference between revisions

Revision as of 22:27, 27 November 2023

Revision as of 10:07, 3 December 2023

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The [[Linux kernel]] notably makes wide use of self-modifying code; it does so to be able to distribute a single binary image for each major architecture (e.g. [[IA-32]], [[x86-64]], 32-bit [[ARM architecture family|ARM]], [[ARM64]]...) while adapting the kernel code in memory during boot depending on the specific CPU model detected, e.g. to be able to take advantage of new CPU instructions or to work around hardware bugs.<ref name="linux_self_modifying_Paltsev">{{cite web |author-last=Paltsev |author-first=Evgeniy |title=Self Modifying Code in Linux Kernel - What, Where and How |date=2020-01-30 |url=https://talk.telematika.org/2019/all/self_modifying_code_in_linux_kernel_-_what_where_and_how/ |access-date=2022-11-27}}</ref><ref name="linux_self_modifying_altinstructions">{{cite web |author-last=Wieczorkiewicz |author-first=Pawel |title=Linux Kernel Alternatives |url=https://grsecurity.net/linux_kernel_alternatives |access-date=2022-11-27}}</ref> To a lesser extent, the [[DR-DOS]] kernel also optimizes speed-critical sections of itself at loadtime depending on the underlying processor generation.<ref name="Caldera_1997_DOSSRC"/><ref name="Paul_1997_OD-A3"/><ref group="nb" name="NB_DR-DOS_386"/>

Regardless, at a [[Meta (prefix)|meta-level]], programs can still modify their own behavior by changing data stored elsewhere (see [[metaprogramming]]) or via use of [[type polymorphism|polymorphism]].

==={{anchor|Synthesis}}Massalin's Synthesis kernel===