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

[Rene Herman]

On 08/12/2007 02:56 AM, Jesper Juhl wrote:

> (whoops, forgot to add maintainer to Cc - now added)

Ehm... too late...

> 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.
diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
index 5acc6c4..fa2eec8 100644
--- a/drivers/block/cciss.c
+++ b/drivers/block/cciss.c
@@ -2609,13 +2609,13 @@ static void do_cciss_request(request_queue_t *q)
 		} else {
 			c->Request.CDBLen = 16;
 			c->Request.CDB[1]= 0;
-			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;
-			c->Request.CDB[5]= (start_blk >> 32) & 0xff;
-			c->Request.CDB[6]= (start_blk >> 24) & 0xff;
-			c->Request.CDB[7]= (start_blk >> 16) & 0xff;
-			c->Request.CDB[8]= (start_blk >>  8) & 0xff;
+			c->Request.CDB[2]= ((u64)start_blk >> 56) & 0xff;	//MSB
+			c->Request.CDB[3]= ((u64)start_blk >> 48) & 0xff;
+			c->Request.CDB[4]= ((u64)start_blk >> 40) & 0xff;
+			c->Request.CDB[5]= ((u64)start_blk >> 32) & 0xff;
+			c->Request.CDB[6]= ((u64)start_blk >> 24) & 0xff;
+			c->Request.CDB[7]= ((u64)start_blk >> 16) & 0xff;
+			c->Request.CDB[8]= ((u64)start_blk >>  8) & 0xff;
 			c->Request.CDB[9]= start_blk & 0xff;
 			c->Request.CDB[10]= (creq->nr_sectors >>  24) & 0xff;
 			c->Request.CDB[11]= (creq->nr_sectors >>  16) & 0xff;