| Message ID | 1377275745-8942-1-git-send-email-peter.maydell@linaro.org |
|---|---|
| State | Accepted |
| Commit | 127c84e1a52f11bf418cc2d3bf804da5091a190a |
| Headers | show |
On 08/23/2013 10:35 AM, Peter Maydell wrote: > The expression "1LL << 63" tries to shift the 1 into the sign bit of a > 'long long', which provokes a clang sanitizer warning: > > runtime error: left shift of 1 by 63 places cannot be represented in type 'long long' Yep, C99 6.5.7p3 states it is undefined to shift a signed number left across the sign bit: "The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with zeros. If E1 has an unsigned type, the value of the result is E1 × 2E2 , reduced modulo one more than the maximum value representable in the result type. If E1 has a signed type and nonnegative value, and E1 × 2E2 is representable in the result type, then that is the resulting value; otherwise, the behavior is undefined." Qemu assumes twos-complement arithmetic with sane signed left shifts, but without a way to tell the compiler our assumptions, it's easier to just stick with well-defined unsigned shifts. > > Use "1ULL << 63" as the definition of QCOW_OFLAG_COPIED instead > to avoid this. For consistency, we also update the other QCOW_OFLAG > definitions to use the ULL suffix rather than LL, though only the > shift by 63 is undefined behaviour. > > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> > --- > block/qcow2.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) Reviewed-by: Eric Blake <eblake@redhat.com>
Am 23.08.2013 um 18:35 hat Peter Maydell geschrieben: > The expression "1LL << 63" tries to shift the 1 into the sign bit of a > 'long long', which provokes a clang sanitizer warning: > > runtime error: left shift of 1 by 63 places cannot be represented in type 'long long' > > Use "1ULL << 63" as the definition of QCOW_OFLAG_COPIED instead > to avoid this. For consistency, we also update the other QCOW_OFLAG > definitions to use the ULL suffix rather than LL, though only the > shift by 63 is undefined behaviour. > > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Thanks, applied to the block branch. Kevin
diff --git a/block/qcow2.h b/block/qcow2.h index dba9771..365a17e 100644 --- a/block/qcow2.h +++ b/block/qcow2.h @@ -40,11 +40,11 @@ #define QCOW_MAX_CRYPT_CLUSTERS 32 /* indicate that the refcount of the referenced cluster is exactly one. */ -#define QCOW_OFLAG_COPIED (1LL << 63) +#define QCOW_OFLAG_COPIED (1ULL << 63) /* indicate that the cluster is compressed (they never have the copied flag) */ -#define QCOW_OFLAG_COMPRESSED (1LL << 62) +#define QCOW_OFLAG_COMPRESSED (1ULL << 62) /* The cluster reads as all zeros */ -#define QCOW_OFLAG_ZERO (1LL << 0) +#define QCOW_OFLAG_ZERO (1ULL << 0) #define REFCOUNT_SHIFT 1 /* refcount size is 2 bytes */
The expression "1LL << 63" tries to shift the 1 into the sign bit of a 'long long', which provokes a clang sanitizer warning: runtime error: left shift of 1 by 63 places cannot be represented in type 'long long' Use "1ULL << 63" as the definition of QCOW_OFLAG_COPIED instead to avoid this. For consistency, we also update the other QCOW_OFLAG definitions to use the ULL suffix rather than LL, though only the shift by 63 is undefined behaviour. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> --- block/qcow2.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)