Re: [HACKERS] Constifying numeric.c's local vars

Mark Dilger <hornschnorter(at)gmail(dot)com> writes:
>> This means that the const variable 'const_zero' contains a pointer that is
>> non-const, pointing at something that is static const, stored in read only
>> memory. Yikes.

> I still believe this is unsafe.

I'm with Andres: I don't see the problem. It's true that we've casted
away a chance for the compiler to notice a problem, but that's not the
only defense against problems. If we did try to modify const_zero,
what should happen now is that we get a SIGSEGV from trying to scribble
on read-only memory. But that's actually a step forward from before.
Before, we'd have successfully modified the value of const_zero and
thereby silently bollixed subsequent computations using it. Since,
in fact, the code should never try to modify const_zero, the SIGSEGV
should never happen. So effectively we have a hardware-enforced Assert
that we don't modify it, and that seems good.

As far as compiler-detectable mistakes go, Andres' changes to declare
various function inputs as const seem like a pretty considerable
improvement too, even if they aren't offering 100% coverage.

regards, tom lane