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

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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>
This commit is contained in:
Iustin Pop 2019-02-22 01:20:03 +01:00 committed by Martin K. Petersen
parent 5c17f87abb
commit 6f46f718fc
2 changed files with 2 additions and 2 deletions
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2
drivers/scsi/osst.c
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@ -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))

2
drivers/scsi/st.c
View File

@ -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 */