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===Assembly language===
Self-modifying code is quite straightforward to implement when using [[assembly language]]. Instructions can be dynamically created in [[computer memory|memory]] (or else overlaid over existing code in non-protected program storage),<ref name="HP9100A_1998"/> in a sequence equivalent to the ones that a standard compiler may generate as the [[object code]]. With modern processors, there can be unintended [[side effect (computer science)|side effect]]s on the [[CPU cache]] that must be considered. The method was frequently used for testing 'first time' conditions, as in this suitably commented [[IBM/360]] [[assembler (computer programming)|assembler]] example. It uses instruction overlay to reduce the [[instruction path length]] by (N×1)−1 where N is the number of records on the file (−1 being the [[computational overhead|overhead]] to perform the overlay).
SUBRTN NOP OPENED FIRST TIME HERE?
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* [[Self-modifying computer virus]]
* [[Self-hosting (compilers)|Self-hosting]]
* [[Synthetic programming]]
* [[Compiler bootstrapping]]
* [[Patchable microcode]]
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<ref name="Caldera_1997_DOSSRC">{{cite web |title=Caldera OpenDOS Machine Readable Source Kit (M.R.S) 7.01 |publisher=[[Caldera (company)|Caldera, Inc.]] |date=1997-05-01 |url=https://archive.sundby.com/retro/DR-DOS/dossrc.zip |access-date=2022-01-02 |url-status=dead |archive-url=https://web.archive.org/web/20210807095409/https://archive.sundby.com/retro/DR-DOS/dossrc.zip |archive-date=2021-08-07}} [https://web.archive.org/web/20220102102656/https://archive.sundby.com/retro/OpenDOS/OPENDOS_7.01_CODE.ZIP]</ref>
<ref name="Paul_1997_OD-A3">{{cite web |author-first=Matthias R. |author-last=Paul |title=Caldera OpenDOS 7.01/7.02 Update Alpha 3 IBMBIO.COM README.TXT |url=http://www.uni-bonn.de/~uzs180/download/ibmbioa3.zip |date=1997-10-02 |access-date=2009-03-29 |url-status=dead |archive-url=https://web.archive.org/web/20031004074600/http://www-student.informatik.uni-bonn.de/~frinke/ibmbioa3.zip |archive-date=2003-10-04}} [https://web.archive.org/web/20181225154705/http://mirror.macintosharchive.org/max1zzz.co.uk/+Windows%20&%20DOS/DOS/System/Novell/Support/Bins/Op702src.zip<!-- Op702src.zip is an unofficial renamed distribution of the ibmbioa3.zip file -->]</ref>
<ref name="HP9100A_1998">{{cite web |title=HP 9100A/B |date=1998 |work=MoHPC - The Museum of HP Calculators |at=Overlapped Data and Program Memory / Self-Modifying Code|url=https://www.hpmuseum.org/hp9100.htm |access-date=2023-09-23 |url-status=live |archive-url=https://web.archive.org/web/20230923125424/https://www.hpmuseum.org/hp9100.htm |archive-date=2023-09-23}}</ref>
}}
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