linux-kernel - [PATCH] Re: cciss: warning: right shift count >= width of type

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Date:	Sun, 12 Aug 2007 03:21:57 +0200
From:	Rene Herman <rene.herman@...il.com>
To:	Jesper Juhl <jesper.juhl@...il.com>
CC:	linux-scsi@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] Re: cciss: warning: right shift count >= width of type

On 08/12/2007 02:28 AM, Jesper Juhl wrote:

> I've been building some randconfig kernels lately and I've noticed 
> this in a few builds : 
> 
> drivers/block/cciss.c:2614: warning: right shift count >= width of type
> drivers/block/cciss.c:2615: warning: right shift count >= width of type
> drivers/block/cciss.c:2616: warning: right shift count >= width of type
> 
> The code in question is this : 
> 
> static void do_cciss_request(struct request_queue *q)
> {
> ...
>         sector_t start_blk;
> ...
>                         c->Request.CDB[2]= (start_blk >> 56) & 0xff;    //MSB
>                         c->Request.CDB[3]= (start_blk >> 48) & 0xff;
>                         c->Request.CDB[4]= (start_blk >> 40) & 0xff;
> ...
> }
> 
> 
> The problem stems from these lines in include/linux/types.h : 
> ...
> #ifdef CONFIG_LBD
> typedef u64 sector_t;
> #else
> typedef unsigned long sector_t;
> #endif
> ...
> 
> So on a 32bit arch without CONFIG_LBD, sector_t is going to be 32 bits wide.
> Thus it seems gcc is absolutely right in complaining about those 
> 56, 48 & 40 bit shifts, since they are indeed wider than the type 
> in the "!CONFIG_LBD on a 32bit arch" case.
> 
> 
> I must admit that I have no idear what the proper way to deal with 
> that is, so I'll just report it so hopefully someone else can fix it.
> 
> By the way; I'm building current Linus git tree, head at commit 
> ac07860264bd2b18834d3fa3be47032115524cea

Well, given that it's explicitly treating start_blk as a 64-bit value, the 
proper fix is probably to cast start_blk to an actual (guaranteed) 64-bit 
value. Untested, uncompiled, and someone else may disagree:

Rene.

View attachment "cciss.diff" of type "text/plain" (1175 bytes)