Talk:IBM Basic assembly language and successors: Difference between revisions

Revision as of 14:00, 6 June 2015

Revision as of 15:38, 6 June 2015

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[[User:Somitcw|Somitcw]] ([[User talk:Somitcw|talk]]) 16:17, 29 May 2015 (UTC)

== "HellHello World" does not need savearea ==

The "Hello World" example stacks a new savearea. This is not necessary, because the "WTO" ("write to operator") eventually expands into a "supervisor call" hardware instruction. Supervisor call handlers in the operating system save and restore registers into their own savearea, not into the savearea pointed to by register 13 upon invocation. Savearea's typically are needed if routines are invoked by a CALL macro instruction, which expands into a BAL or BALR instruction, that invokes the required routine directly, without supervisor involvement (supervisor = operating system).