scsi: st: osst: Remove negative constant left-shifts (6f46f718) · Commits · 戴 / test

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>

drivers/scsi/osst.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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))

drivers/scsi/st.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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 */

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