linux-kernel - Re: [PATCH 3.13-rc1] xen-blkfront: Silence pfn maybe-uninitialized warning

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Message-ID: <528554AC.5080607@canonical.com>
Date:	Thu, 14 Nov 2013 14:54:36 -0800
From:	Tim Gardner <tim.gardner@...onical.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
CC:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	"roger.pau@...rix.com" <roger.pau@...rix.com>
Subject: Re: [PATCH 3.13-rc1] xen-blkfront: Silence pfn maybe-uninitialized
 warning

On 11/14/2013 02:24 PM, Konrad Rzeszutek Wilk wrote:
> Tim Gardner <tim.gardner@...onical.com> wrote:
>> pfn cannot actually be used unless (!info->feature_persistent), nor
>> is pfn accessed in get_grant() unless (!info->feature_persistent),
>> but silence this warning anyway. gcc-4.8
>> 
>> drivers/block/xen-blkfront.c: In function 'do_blkif_request': 
>> drivers/block/xen-blkfront.c:508:20: warning: 'pfn' may be used 
>> uninitialized in this function [-Wmaybe-uninitialized] 
>> gnt_list_entry = get_grant(&gref_head, pfn, info); ^ 
>> drivers/block/xen-blkfront.c:492:19: note: 'pfn' was declared here 
>> unsigned long pfn;
>> 
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> Cc: Boris
>> Ostrovsky <boris.ostrovsky@...cle.com> Cc: David Vrabel
>> <david.vrabel@...rix.com> Signed-off-by: Tim Gardner
>> <tim.gardner@...onical.com> --- drivers/block/xen-blkfront.c |    2
>> +- 1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/block/xen-blkfront.c 
>> b/drivers/block/xen-blkfront.c index 432db1b..5f926de 100644 ---
>> a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c 
>> @@ -489,7 +489,7 @@ static int blkif_queue_request(struct request
>> *req)
>> 
>> if ((ring_req->operation == BLKIF_OP_INDIRECT) && (i %
>> SEGS_PER_INDIRECT_FRAME == 0)) { -				unsigned long pfn; +
>> unsigned long uninitialized_var(pfn);
>> 
>> if (segments) kunmap_atomic(segments);
> 
> I have a similar patch from Roger that sets pfn=0.
> 
> Roger could you repost your patch please or if you feel that this
> patch makes sense then comment on it?
> 
> Thanks.
> 

The advantage of uninitialized_var() is that it doesn't actually
generate any code (or so it says in the header).

rtg
-- 
Tim Gardner tim.gardner@...onical.com
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