[cfe-dev] Integer overflow checking

[David Chisnall]

On 17 May 2009, at 00:17, Martin Doucha wrote:

> Perhaps I should clarify. The goal of my thesis is to detect and  
> report
> newbie mistakes. That includes unsigned overflow because although it's
> well defined, it's almost certainly a mistake in newbie code. What
> language standard says about the behavior is one thing. Whether or not
> it's considered a bug in actual code is quite another. Anyway, you're
> free to do anything you wish with that patch.

I'd like to add that there is currently a proposal before WG14 from  
the secure coding group to make it possible to trap[1] on both signed  
and unsigned overflow.  Even though a signed overflow is well defined,  
a huge body of existing code does the wrong thing in the presence of  
overflow and making code .

The original -ftrapu patch that was reverted was almost expressive  
enough to implement all of the current proposals in the library (the  
flag was/is too coarse-grained, but the stuff in CodeGen was usable).   
The new patch provides a less-useful trap function.

David

[1] C1x has a proposed callback mechanism for things like this, a bit  
like a subset of Lisp resumable exceptions handling (without stack  
unwinding).