Re: reliability features and Optimization techniques

On Monday, April 29, 2019 at 12:31:16 AM UTC+2, Bart wrote:
> On 26/04/2019 09:33, alexfrunews@gmail.com wrote:
> Jan Ziak wrote:
> >> I don't fully understand. Are you suggesting to add buffer overflow
> checks to
> >> the C language?
> >
> > No. However, I think the language could provide a designated
> > tuple-like type containing a pointer and a count/size and maybe some
> > functions/macros to check the range. Or something like that. But...
>
> Yes, that's a feature I call a slice, which is a pointer and length.
> That would be quite useful, except that typical C doesn't even use
> arrays properly:
>
> Instead of a function parameter being of type T(*)[] (pointer to array
> of T), usually it is just T* (pointer to its element type). The array is
> implied, which means it is possible to pass a pointer to anything: a
> single T value; 2 successive T members of a struct. Or even just the
> middle of an array.
>
> It is undisciplined, with the 'length' of the implied array of such a
> pointer being badly defined. (It can't even be the bounds of an
> allocated memory block, because that can be bigger than the array.)
>
> So C is pretty much a lost cause.


You don't necessarily need to introduce slices to C in order to enable the
safety checks (slice-like safety checks). By sacrificing a bit of runtime
performance and slightly increasing memory consumption, the generated assembly
code can perform the checks even if the pointer size remains to be 8 bytes (or
4 bytes in case of a 32-bit address space).


Sincerely
Jan

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