Re: [Qemu-devel] [PATCH] Fix subtle integer overflow bug in memory API

[Avi Kivity]

On 09/15/2011 10:38 AM, Paolo Bonzini wrote:
> On 09/15/2011 04:34 AM, David Gibson wrote:
> > explicit "if (a + b)<  a" tests in some places.
>
> Please wrap these in a macro, since the addition has to be done in an 
> unsigned type.  Otherwise overflow is undefined.

It doesn't help if the overflow is defined but produces an incorrect result.

The fact is we need a 64+N bit datatype, where N is the nesting level of 
MemoryRegions (including aliases).  Each nesting level can overflow a 
bit.  Right now the only viable options seems to be #define 64 60, but 
I'll be happy to consider others.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.