scsi: st: osst: Remove negative constant left-shifts

Negative constant left-shift is undefined behaviour in the C standard, and
as such newer versions of clang (at least) warn against it. GCC supports it
for a long time, but it would be better to remove it and rely on defined
behaviour.

My understanding is "~(-1 << N)" in 2's complement is intended to generate
a bit pattern of zeroes ending with N '1' bits. The same can be achieved by
"(1 << N) - 1" in a well-defined way, so switch to it to remove the
warning.

Tested: building a kernel with generic SCSI tape, and checking basic
operations (mt status, mt eject) on a real LTO unit. Cannot test the osst
driver.

Signed-off-by: Iustin Pop <iustin@k1024.org>
Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/osst.c b/drivers/scsi/osst.c
index 664c123..be3c73e 100644 (file)
--- a/drivers/scsi/osst.c
+++ b/drivers/scsi/osst.c
@@ -139,7 +139,7 @@ static int debugging = 1;
 #define OSST_TIMEOUT (200 * HZ)
 #define OSST_LONG_TIMEOUT (1800 * HZ)
 
-#define TAPE_NR(x) (iminor(x) & ~(-1 << ST_MODE_SHIFT))
+#define TAPE_NR(x) (iminor(x) & ((1 << ST_MODE_SHIFT)-1))
 #define TAPE_MODE(x) ((iminor(x) & ST_MODE_MASK) >> ST_MODE_SHIFT)
 #define TAPE_REWIND(x) ((iminor(x) & 0x80) == 0)
 #define TAPE_IS_RAW(x) (TAPE_MODE(x) & (ST_NBR_MODES >> 1))

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 7c7a742..19c022e 100644 (file)
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -169,7 +169,7 @@ static int debugging = DEBUG;
 
 /* Remove mode bits and auto-rewind bit (7) */
 #define TAPE_NR(x) ( ((iminor(x) & ~255) >> (ST_NBR_MODE_BITS + 1)) | \
-    (iminor(x) & ~(-1 << ST_MODE_SHIFT)) )
+       (iminor(x) & ((1 << ST_MODE_SHIFT)-1)))
 #define TAPE_MODE(x) ((iminor(x) & ST_MODE_MASK) >> ST_MODE_SHIFT)
 
 /* Construct the minor number from the device (d), mode (m), and non-rewind (n) data */