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

From: Rene Herman
Date: Sat Aug 11 2007 - 21:58:23 EST


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@xxxxxxxxx> 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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