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Re: [Xen-devel] [PATCH] fix uninitialized variable error in do_poll()
- To: Wei Liu <wei.liu2@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 5 Oct 2018 12:43:13 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 05 Oct 2018 11:43:25 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 05/10/18 12:25, Wei Liu wrote:
> On Fri, Oct 05, 2018 at 05:22:29AM -0600, Jan Beulich wrote:
>>>>> On 05.10.18 at 12:28, <wei.liu2@xxxxxxxxxx> wrote:
>>> On Fri, Oct 05, 2018 at 04:12:10AM -0600, Jan Beulich wrote:
>>>> Now that CONFIG_HVM can (and should) be turned off for the shim, gcc 8.2
>>>> apparently is no longer sure that "port" is indeed initialized at
>>>>
>>>> if ( sched_poll->nr_ports == 1 )
>>>> v->poll_evtchn = port;
>>>>
>>>> It doesn't look to be impossible for the compiler to prove it is not,
>>>> but we also can't rely on that to be the case. Add an initializer.
>>>>
>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>> TBH I fail to see how CONFIG_HVM would affect do_poll. Also there is
>>> already build test with gcc 8.2 which never discovered the issue you
>>> described.
>> I can't explain the sudden diagnostic too (without taking apart what
>> exactly the compiler does), but the same config (just with HVM=y)
>> built fine before. Without any further insight (which I don't think is
>> worth the time) I don't see how I could improve the description.
> Oh well.
>
> Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
TBH, I'm not sure that relying on DCE is a good longterm option. It
will almost certainly break the build at -O0, and our code really should
build at all optimisation levels. (There is still a fair chunk of work
to make -O3 work, which I haven't got time for atm).
~Andrew
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