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authorIustin Pop <iustin@k1024.org>2019-02-22 01:20:03 +0100
committerMartin K. Petersen <martin.petersen@oracle.com>2019-02-27 09:10:16 -0500
commit6f46f718fcbe7b80ac95e4f4e1bade6efbcff84e (patch)
treeefec70cd0a6b86782511270426eced9cad412f79
parent5c17f87abb1a86eb4d2a108477e56389622cf195 (diff)
downloadlinux-6f46f718fcbe7b80ac95e4f4e1bade6efbcff84e.tar.bz2
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>
-rw-r--r--drivers/scsi/osst.c2
-rw-r--r--drivers/scsi/st.c2
2 files changed, 2 insertions, 2 deletions
diff --git a/drivers/scsi/osst.c b/drivers/scsi/osst.c
index 664c1238a87f..be3c73ebbfde 100644
--- 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 7c7a742a5ef7..19c022e66d63 100644
--- 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 */