Re: [Xen-devel] [PATCH 4/8] tools/xenalyze: Mark unreachable code as unreachable

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 25/02/16 15:28, Ian Campbell wrote:
> On Thu, 2016-02-25 at 15:09 +0000, George Dunlap wrote:
>> On 25/02/16 15:03, Ian Campbell wrote:
>>> On Thu, 2016-02-25 at 14:48 +0000, George Dunlap wrote:
>>>> ...so that coverity knows it's unreachable.
>>>
>>> I would not be surprised if Coverity starts complaining about the dead
>>> code
>>> once this is in place. fprintf + abort is probably what would be wanted
>>> to
>>> placate it in this case.
>>
>> Hrm -- it would be nice to have a way to figure out what coverity likes
>> without having to actually check something into the tree...
> 
> If this code is truly unreachable (i.e. it is after a while(1) with no
> breaks etc) then you should just drop the logging since it will never be
> reached, then the __builtin_unreachable() is appropriate.
> 
> If, as the log message implies, this is code which _should_ be unreachable
> by design but would be reached in the case of a logic error in the
> preceding code then what you want is either fprintf()+abort() or maybe
> assert().

Right -- well basically error(ASSERT,...) is a custom abort().  But in
the current case it isn't actually doing anything more than an abort()
would, so perhaps I should use that instead (since coverity knows about
abort() and assert() but not my custom function).

> But Coverity seems to have disproven this possibility, correctly AFAICT
> because all of the preceeding cases of the if chain end with a goto, this
> removing the logging and leaving the __builtin_unreachable() is the way to
> go.
> 
> I don't think this is really about what would keep Coverity happy, more to
> do with the intended semantics of execution reaching this point.

It's already doing what I want mostly; so maybe I should just close the
bug as "intentional" (or "needs modelling" or something).

 -George


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