I admit this was a bandaid solution. After catching two bad uses of SharedBuffer, I wanted systematically detect and eradicate the problem at this site.  Only checking in a few places is like only clearing the snow off the third stair because that's where I slipped last time. We had an e-mail thread about this a while back, but it kind of died off with no follow-up.  Thanks for bringing this back to the table.

FWIW, the STRICT_ARG_TYPE macro was used here to catch a pattern where a value that was originally a size_t got transiently stored in a 'long' local variable before being passed to SharedBuffer.  It was the first conversion (to long) that was dangerous, but I had no way to systematically instrument SharedBuffer to catch that pattern.

Unsafe casts are everywhere, so it would be hard to block them globally.  A more reasonable approach would be to turn on unsafe cast errors specifically for conversions to and from size_t and ptrdiff_t to focus on the conversions most susceptible of causing memory errors (and therefore security vulnerabilities).


thakis@: You said it would be possible to do this with a custom error in clang.
Is that going to happen?

Incidentally, MSVC warning C4267 is specifically for conversion from size_t to a smaller type, as you suggest.

It's unlikely to be feasible to turn this on globally yet, but we could probably turn it on in all or part of Blink.

That is very interesting. MSVC would give us coverage for a 64-bit build and a 32-bit build, which is pretty much all we need.

I would suggest picking a project or projects you think gives sufficient coverage to catch at least the SharedBuffer issues you saw, and try enabling this warning just for those, plus disable warnings-as-errors for the same projects.  Run the change through the trybots (or build locally if you have a Windows machine) and see how many errors you get (hence the disabling warnings-as-errors, so the build doesn't terminate).  If the number is reasonably small, fix those and turn the warning on for those projects, and eliminate the changes previously made here.  If the number is large, send the list to me for help and we can figure something out.