Re: [Xen-devel] [PATCH for-4.10 2/2] ubsan: disable unaligned access checks

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Oct 17, 2017 at 01:56:18PM +0100, Wei Liu wrote:
> On Tue, Oct 17, 2017 at 12:36:44PM +0100, Roger Pau Monne wrote:
> > Currently there are many offenders of the unaligned access checks,
> > which makes booting with the unaligned check a PVH Dom0 impossible.
> > 
> > The main offenders seem to be the ACPI code, the VMX code and
> > specially the intremap code (set_ire_sid).
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > ---
> > Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> > Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > Cc: Jan Beulich <jbeulich@xxxxxxxx>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > Cc: Tim Deegan <tim@xxxxxxx>
> > Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> > Cc: Julien Grall <julien.grall@xxxxxxx>
> > ---
> > I'm not sure whether we prefer to fix the offenders, or just disable
> > the alignment wholesale. In any case if we decide to disable the
> > check, the patch should have vary low impact, and hence should be
> > committed to 4.10 on the base that it only affects ubsan, which is not
> > enabled by default and not to be used on production systems.
> 
> I would very much like to fix the offenders but if the fixes turn out to
> be cumbersome, so be it.
> 
> What is wrong to leave this enabled? Each location is reported once,
> right?

With clang it's reported every time it's hit AFAICT (certainly more
than once).

Roger.

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