When running with SMMUv3 and UBSAN enabled on arm64, there are a lot of
warnings printed related to shifting into sign bit in generic_fls()
as it takes parameter of type int.
Example:
(XEN) UBSAN: Undefined behaviour in ./include/xen/bitops.h:69:11
(XEN) left shift of 134217728 by 4 places cannot be represented in type 'int'
It does not make a lot of sense to ask for the last set bit of a negative
value. We don't have a direct user of this helper and all the wrappers
pass value of type unsigned {int,long}.
Linux did the same as part of commit:
3fc2579e6f16 ("fls: change parameter to unsigned int")
To keep consistency between the helpers, take the opportunity to:
- replace __inline__ with inline,
- modify generic_ffs() to take parameter of type unsigned int as well
(currently no user and the only wrapper generic_ffsl() passes unsigned
long).
Signed-off-by: Michal Orzel <[email protected]>
---
Changes in v2:
- as requested by Jan, s/__inline__/inline/ and modify generic_ffs()
for consistency
It looks like generic_fls() is only used by Arm and invoked only if
the arguement passed is a compile time constant. This is true for SMMUv3
which makes use of ffs64() in FIELD_{PREP,GET} macros. generic_ffs() has no
user at the moment.
Note for the future:
The return type could be unsigned as well. However, looking at all variations
of the helpers to find first set/clear in the codebase, returning int is the
de-facto standard. Changing the return type of the title helpers would result
in inconsistency or require to do modifications in other places which is not
something I want to do at this stage of release.
---
xen/include/xen/bitops.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/xen/include/xen/bitops.h b/xen/include/xen/bitops.h
index 654f525fb437..edd6817d5356 100644
--- a/xen/include/xen/bitops.h
+++ b/xen/include/xen/bitops.h
@@ -18,7 +18,7 @@
* differs in spirit from the above ffz (man ffs).
*/
-static inline int generic_ffs(int x)
+static inline int generic_ffs(unsigned int x)
{
int r = 1;
@@ -51,7 +51,7 @@ static inline int generic_ffs(int x)
* fls: find last bit set.
*/
-static __inline__ int generic_fls(int x)
+static inline int generic_fls(unsigned int x)
{
int r = 32;
--
2.25.1
