[Simh] VAX emulation issues on Raspberry Pi

[Timothe Litt]

On 31-Jul-18 13:46, Paul Koning wrote:
> No, but thanks for that pointer. The paper I was thinking about is
> listed in the references:
> Xi Wang, Haogang Chen, Alvin Cheung, Zhihao Jia, Nickolai Zeldovich, and M. Frans Kaashoek. 2012a. Undefined behavior: What happened to my code? In Proceedings of the 3rd Asia-Pacific Workshop on Systems.
https://people.csail.mit.edu/nickolai/papers/wang-undef-2012-08-21.pdf

Seems to be a rehash of some well-known stuff - that was pretty well
known even in 2012.

In additions to -Wall, I also used to compile SimH with -pedantic and -Werror.  And usually one of the -std flags.

> Hm, -pedantic is specificially intended to be "the warnings that aren't really useful for general use and real code".
But I often found that if I tripped one, my mind was wandering and
something else was likely not quite right :-)
>> Another big potential gotcha in SimH is the heavy use of casts, and type aliasing rules (the latter especially problematic in subroutine calls).
> Yes, aliasing is a big problem area.  If you get any warnings about strict aliasing, fixing them (via unions) is a good idea.  Alternatively, fno-strict-aliasing can be used but that comes with a performance cost and is not the best answer.
>
I'm of the school that says "fix, don't disable".  Especially if you
want your code to work with more than one compiler.  But it can be
painful with legacy code.

I also recommend "C is not a low-level language
<https://queue.acm.org/detail.cfm?id=3212479>" in the July issue of
CACM.  It makes some useful points that apply here.



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