Jon Elson jonelson126 at gmail.com
Sat Jan 14 20:23:16 CST 2017

On 01/14/2017 02:29 PM, Cameron Kaiser wrote:
>> Oh my!  You couldn't have a subroutine that called another
>> subroutine, using their surroutine call/return instructions!  I never
>> knew that!
> Strictly speaking, that would still be true of any CPU that uses a link
> register instead of a stack for return addresses (most RISC CPUs including
> PowerPC, ARM and MIPS; TMS 9900; etc). These architectures have to explicitly
> save the return address in the LR as part of the callee function prologue
> just as these older systems would have had to (or the equivalent operation).
Yes, this fits into the context of the System/360.  I can't imagine how 
much CPU time was wasted when people forgot to save R14 before calling a 
deeper subroutine, causing an infinite loop.


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