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Re: [Qemu-devel] [PATCH v2] memory: use signed arithmetic


From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH v2] memory: use signed arithmetic
Date: Wed, 03 Aug 2011 07:59:27 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:5.0) Gecko/20110707 Thunderbird/5.0

On 08/03/2011 01:56 AM, 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.
> 
> Signed-off-by: Avi Kivity <address@hidden>

Signed-off-by: Richard Henderson <address@hidden>


r~



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