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@xxxxxxxxx> --- (with apologies if I made mistakes in the CC list) drivers/scsi/osst.c | 2 +- drivers/scsi/st.c | 2 +- 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 7ff22d3f03e3..eca84caed6ff 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 */ -- 2.20.1
