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Re: [PATCH v2 3/3] x86/pv: Address Coverity complaint in check_guest_io_breakpoint()
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 15 Aug 2024 17:45:43 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Matthew Barnes <matthew.barnes@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 15 Aug 2024 15:45:49 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.08.2024 15:16, Andrew Cooper wrote:
> Commit 08aacc392d86 ("x86/emul: Fix misaligned IO breakpoint behaviour in PV
> guests") caused a Coverity INTEGER_OVERFLOW complaint based on the reasoning
> that width could be 0.
>
> It can't, but digging into the code generation, GCC 8 and later (bisected on
> gotbolt) choose to emit a CSWITCH lookup table, and because the range (bottom
> 2 bits clear), it's a 16-entry lookup table.
>
> So Coverity is correct, given that GCC did emit a (dead) logic path where
> width stayed 0.
>
> Rewrite the logic. Introduce x86_bp_width() which compiles to a single basic
> block, which replaces the switch() statement. Take the opportunity to also
> make start and width be loop-scope variables.
>
> No practical change, but it should compile better and placate Coverity.
>
> Fixes: 08aacc392d86 ("x86/emul: Fix misaligned IO breakpoint behaviour in PV
> guests")
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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