linux-kernel - Re: [PATCH] stop gcc warning about uninitialized 'dev' in ata_scsi_scan

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Date:	Thu, 16 Oct 2008 15:08:55 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Elias Oltmanns <eo@...ensachen.de>
CC:	Alex Chiang <achiang@...com>, jeff@...hat.com,
	linux-ide@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] stop gcc warning about uninitialized 'dev' in	ata_scsi_scan_host

Elias Oltmanns wrote:
>> I think the current policy is blaming gcc but I also added quite a few
>> bogus NULL initializations here and there and caught several bugs thanks
>> to those warnings.  We can think about adding an additional annotation
>> with leading double underbars which indicate that certain pointer
>> arguments to functions expect (or are okay with) pointers to
>> uninitialized variables which should be able to remove many of those
>> spurious warnings (on the caller side, the compiler can ignore the
>> warning and on the callee side the compiler can check whether it's being
>> dereferenced without being written to).  Does anyone know whether gcc
>> already has that type of annotation?
> 
> Well, I don't know of this particular kind of annotation. However, I
> don't quite see how that would solve the reported issue.

I was thinking about the warning in sata_via.c and for such cases the
compiler doesn't have any other way of figuring out whether it's okay
or not (the sata_via case, the compiler can actually do as the callee
is in the same file but you know what I mean).

> Here, dev is a local variable and the warning is generated due to
> the line
> 
> 		if (dev != last_failed_dev) {
> 
> For this sort of thing we have:
> 
> 	struct ata_device *uninitialized_var(dev);

Ah.. thanks.

> Or is that precisely the thing you did *not* want?

I don't know.  Later versions of gcc doesn't issue warning because it
knows "if (!link)" always triggers if dev is not initialized.  I don't
think we should be adding those annotations if the current gen
compiler can already figure that out as it only decreases
debuggability when something actually gets broken there.

Thanks.

-- 
tejun
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