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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: Calling conventions (particularly 32-bit ARM)
Date: Fri, 10 Jan 2025 01:08:16 +0000
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On Thu, 9 Jan 2025 21:23:30 +0000, Thomas Koenig wrote:

> MitchAlsup1 <mitchalsup@aol.com> schrieb:
>> On Thu, 9 Jan 2025 7:23:57 +0000, Anton Ertl wrote:
>>
>>> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>>> [Someone wrote:]
>>>>> ABI calling conventions tend to be designed to support at least C,
>>>>> including varargs and often also tolerant of differences between the
>>>>> number of arguments in the caller and callee.
>>>>
>>>>I can agree that it's important to support those use-cases (varargs
>>>>obviously, mismatched arg numbers less so),
>>>
>>> You are head of a group of people who design a new architecture (say,
>>> it's 2010 and you design ARM A64, or it's 2014 and you design RISC-V).
>>> Your ABI designer comes to you and tells you that his life would be
>>> easier if it was ok that programs with mismatched arguments don't need
>>> to work.  Would you tell him that they don't need to work?
>>
>> No, I would stand my ground and mandate that they do work.
>
> That can be tricky.  You can read
>
> https://blog.r-project.org/2019/05/15/gfortran-issues-with-lapack/index.html
>
> and its sequel
>
> https://blog.r-project.org/2019/09/25/gfortran-issues-with-lapack-ii/
>
> as a cautionary tale.

Yes, I had to make a nasty ABI work on the HEP (Denelcor)

> To cut this a little shorter:  Assume eight arguments are passed in
> registers, like for My 66000.
>
> Caller calls
>
>   foo (a1, a2, a3, a4, a5, a6, a7, a8);
>
> Callee side:
>
>   foo (a1, a2, a3, a4, a5, a6, a7, a8, a9)
>
> Foo ends with
>
>   bar (b1, b2, b3, b4, b5, b6, b7, b8, b9);
>
> and wants to save stack space, so it stores the value of b9 into
> the space where it was supposed to be, and then branches to bar.
> Result: Stack corruption.
>
> What would you tell your ABI designer in that case?  Don't do tail
> calls, it is better to use more stack space, with all effect on
> stack sizes and locality that would have?

Same response I would give to::

     printf( "%d %d %d %d %d/r", a[i] );

"They deserve what they get".

You will notice that no ISA has ever had a "go jump in the lake"
instruction. For had there been, computers would not have survived
the the present--they would all be in the lake...