Re: A Famous Security Bug

On 2024-03-22, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:

bart <bc@freeuk.com> writes:

On 22/03/2024 17:14, James Kuyper wrote:

[...]

If you want to tell a system not only what a program must do, but
also how it must do it, you need to use a lower-level language than
C.

>
Which one?

>
Good question.
>

I don't think anyone seriously wants to switch to assembly for the
sort of tasks they want to use C for.

>
Agreed.  What some people seem to be looking for is a language that's
about as portable as C, but where every language construct is required
to result in generated code that performs the specified operation.
There's a lot of handwaving in that description.  "C without
optimization", maybe?
>
I'm not aware that any such language exists, at least in the mainstream
(and I've looked at a *lot* of programming languages).  I conclude that
there just isn't enough demand for that kind of thing.

I think you can more or less get something like that with the following
strategy:

- all memory accesses through pointers are performed as written.
- local variables are aggressively optimized into registers.
- basic optimizations:
  - constant folding, dead code elimination.
  - basic control flow ones: jump threading and the like.
  - basic data flow optimizations.
  - peephole, good instruction selection.

In that environment, the way the programmer writes the code is the rest
of the optimization. Want loop unrolling? Write it yourself.


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