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    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.
    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;
    \
     
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