On Fri, 09 Mar 2018 17:16:19 +0100, David Brown 
declaimed the following:

>On 09/03/18 15:13, bartc wrote:

>>
>> I guess simplicity of the call convention wasn't a priority.
>>
>
>Well no, of course it was not a priority.  Why should it be?  Virtually
>no one is interested in the calling conventions - just compiler writers,
>people writing OS context switch routines, and the few dozen people
>writing assembly routines instead of using higher level languages.
>Efficiency of generated code was far and away the priority when AMD made
>the System V AMD64 ABI used by everyone except Windows.  $DEITY only
>knows what MS's priorities were when they scrambled it and made
>something pointlessly different and less efficient - the only think I
>can think of was to make implementation of "printf" a little easier for
>the MSVC compiler writers.

 

 There is always the convention used by Xerox Sigma Fortran-IV.
Non-recursive, non-stack...

 Arguments were passed by putting them immediately after the CALL
(branch and link opcode, and referenced by return address (saved in a
register; I think 15 was the standard) + index. Code was responsible for
incrementing the return address to jump over the arguments. {I don't have
my 40 year old manuals handy, so pseudo-ops...}

...
 stw,9 arg2
 bl,15 mysub
 data arg1 ;normally this would save the address of arg1
arg2 data 0 ;reserved space for storing a "pass by value"



...

mysub lw,9 *15 ;indirect, load arg1 address into 9
  inc,15
  lw,10 *15 ;indirect, load arg2 value into 10
  inc,15
  stw,15 retadd
....
  lw,15 retadd
  ret
retadd data 0 ;space to save return address

 Of course, the pass-by-value semantics would fail for any system that
makes code-space read-only; pass-by-address is a compile time definition.


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 Wulfraed                 Dennis Lee Bieber         AF6VN
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