Re: [Qemu-devel] [PATCH] memory: use signed arithmetic

[malc]

On Tue, 2 Aug 2011, Avi Kivity wrote:

> When trying to map an alias of a ram region, where the alias starts at
> address A and we map it into address B, and A > B, we had an arithmetic
> underflow.  Because we use unsigned arithmetic, the underflow converted
> into a large number which failed addrrange_intersects() tests.
> 
> The concrete example which triggered this was cirrus vga mapping
> the framebuffer at offsets 0xc0000-0xc7fff (relative to the start of
> the framebuffer) into offsets 0xa0000 (relative to system addres space
> start).
> 
> With our favorite analogy of a windowing system, this is equivalent to
> dragging a subwindow off the left edge of the screen, and failing to clip
> it into its parent window which is on screen.
> 
> Fix by switching to signed arithmetic.

http://stackoverflow.com/questions/3679047/integer-overflow-in-c-standards-and-compilers

In other words UB land

[..snip..]

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