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From: George Dunlap <george.dunlap@citrix.com>
To: Ian Campbell <ian.campbell@citrix.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	xen-devel@lists.xen.org
Cc: Ian Jackson <ian.jackson@citrix.com>, Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH 4/8] tools/xenalyze: Mark unreachable code as unreachable
Date: Thu, 25 Feb 2016 15:43:09 +0000	[thread overview]
Message-ID: <56CF210D.4080203@citrix.com> (raw)
In-Reply-To: <1456414126.6225.221.camel@citrix.com>

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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  reply	other threads:[~2016-02-25 15:43 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-25 14:48 [PATCH 0/8] Fixes to Coverity issues reported on xenalyze George Dunlap
2016-02-25 14:48 ` [PATCH 1/8] tools/xenalyze: Close symbol_file after reading it George Dunlap
2016-02-26 12:22   ` Ian Jackson
2016-02-29 16:11     ` Konrad Rzeszutek Wilk
2016-02-25 14:48 ` [PATCH 2/8] tools/xenalyze: Avoid redundant check George Dunlap
2016-02-26 12:23   ` Ian Jackson
2016-02-29 16:15     ` Konrad Rzeszutek Wilk
2016-02-25 14:48 ` [PATCH 3/8] tools/xenalyze: Handle fstat errors properly George Dunlap
2016-02-26 12:25   ` Ian Jackson
2016-03-03 12:28     ` George Dunlap
2016-02-25 14:48 ` [PATCH 4/8] tools/xenalyze: Mark unreachable code as unreachable George Dunlap
2016-02-25 15:03   ` Ian Campbell
2016-02-25 15:09     ` George Dunlap
2016-02-25 15:28       ` Ian Campbell
2016-02-25 15:43         ` George Dunlap [this message]
2016-02-25 15:52           ` Ian Campbell
2016-02-26 12:28             ` Ian Jackson
2016-02-25 14:49 ` [PATCH 5/8] tools/xenalyze: Fix check for error return value George Dunlap
2016-02-26 12:29   ` Ian Jackson
2016-02-29 16:16     ` Konrad Rzeszutek Wilk
2016-02-25 14:49 ` [PATCH 6/8] tools/xenalyze: Fix off-by-one in MAX_CPUS range checks George Dunlap
2016-02-26 12:30   ` Ian Jackson
2016-02-29 16:58     ` George Dunlap
2016-03-03 12:44       ` George Dunlap
2016-02-25 14:49 ` [PATCH 7/8] tools/xenalyze: Fix multiple instances of *HYPERCALL_MAX George Dunlap
2016-02-26 12:33   ` Ian Jackson
2016-02-29 17:29     ` George Dunlap
2016-03-01 13:36       ` Ian Jackson
2016-02-25 14:49 ` [PATCH 8/8] tools/xenalyze: Actually handle case where number of ipi vectors exceeds static max George Dunlap
2016-02-26 12:34   ` Ian Jackson
2016-02-29 16:16     ` Konrad Rzeszutek Wilk

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