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

[Rene Herman <rene.herman@gmail.com>]

On 08/12/2007 03:25 AM, Rene Herman wrote:

> On 08/12/2007 02:56 AM, Jesper Juhl wrote:
>
> > (whoops, forgot to add maintainer to Cc - now added)
>
> Ehm... too late...

Useless followup though -- hp.com rejects me as it feels the SPF neutral 
results gmail sends due to me not using the gmail SMTP server and/or web 
interface is something it wants to listen to.

I see you are @gmail as well, which depending on how you use it might mean 
your are also not able to reach @hp. If anyone can get HP to fix their mail 
setup, that'd be useful.

Rene.


> > On 12/08/07, Jesper Juhl <jesper.juhl@gmail.com> wrote:
> > > Hi,
> > >
> > > 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.

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