Execute instruction: Difference between revisions

Revision as of 20:08, 30 July 2021

Revision as of 20:09, 30 July 2021

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Some architectures support execution of a two-instruction sequence of instructions, notably the GE-600 series. The target instructions [[data alignment|must start on an even-numbered word]].<ref name="GE635"/>

Some architectures support an ''execute'' instruction which operates in a different [[Protection ring|protection and address relocation mode]]. For example, the [[Incompatible Timesharing System|ITS]] PDP-10 paging device supports a [[Protection ring|privileged-mode]] <code>{{mono|XCTR</code>}} 'execute relocated' instruction which allows memory reads, writes, or both to use the user-mode page mappings.<ref>{{cite web|first=J.|last=Holloway|title=Hardware Memo 2 - PDP-10 Paging Device|publisher=[[MIT AI Lab]]|date=February 20, 1970|page=11|url=http://www.bitsavers.org/pdf/mit/ai/ai_600dpi/HW_Memo_2_PDP-10_Paging_Device_Feb1970.pdf}}</ref> Similarly, the [[PDP-10#KL10|KL10]] variant of the PDP-10 supports the privileged instruction <code>{{mono|PXCT</code>}} 'previous context XCT'.<ref name="pdp10">{{cite manual|publisher=[[Digital Equipment Corporation]]|title=DECsystem-10, DECSYSTEM-20 Processor Reference Manual|id=AA-H391A-TK, AD-H391A-T1|date=June 1982|page=2{{hyphen}}63|url=https://www.livingcomputers.org/UI/UserDocs/Tops-10-v7-04/3_DECsystem-10_DECSYSTEM-20_Processor_Reference.pdf}}</ref>

The execute instruction can cause several problems when an ''execute'' instruction points to another one and so on: