linux-kernel - Re: [BUG REPORT] use of unreachable() masks uninitialized variables warnings

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Message-ID: <CAO6TR8VsX8DEQTGE6gwrzXr8QiPoCpv2-rbXq7VAtPz8KN3Ofw@mail.gmail.com>
Date:	Thu, 11 Feb 2016 21:58:42 -0700
From:	Jeff Merkey <linux.mdb@...il.com>
To:	"Theodore Ts'o" <tytso@....edu>, Jeff Merkey <linux.mdb@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG REPORT] use of unreachable() masks uninitialized variables warnings

On 2/11/16, Theodore Ts'o <tytso@....edu> wrote:
> On Thu, Feb 11, 2016 at 11:12:12AM -0700, Jeff Merkey wrote:
>>
>> That's good to know, they could be false positives, but it was kind of
>> wierd behavior caused by that macro.
>
> If it is true, it sounds more like a compiler bug to me.  Any
> statements a BUG() call are unreachable.  If the compiler assumes that
> in the case of:
>
> 	if (a)
> 	        BUG();
> 	printf("foo bar\n");
> 	
> That the printf is not reachable, that's a compiler bug.  And not a
> problem in the BUG() macro.
>
> It might be that it's worthwhile to use other static code analysis
> tools.  Many people will look at warnings from Coverity and clang to
> find potential problems, since these tend to find more warnings than
> just using gcc.  The problem with some of these, including Coverity,
> is that they can be __too__ noisy, and if 90% of the warnings are
> false positives, most people won't take the time to weed out several
> dozen bogus warnings to find the one good one.
>

Did you remove the calls to unreachable() before you did the build?
Remove the call to that function from the BUG() macro, then do a
build, and tell me I am seeing things.

Jeff