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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 17/10/17 13:58, Roger Pau Monné wrote:
> 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).

suppress_report() is supposed to take care of this.  Is Clang feeding in
different ->location information each time through?

~Andrew

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