Messages in this thread Patch in this message | | | From | Arnd Bergmann <> | Subject | Re: [PATCH v3] err.h: allow IS_ERR_VALUE to handle properly more types | Date | Thu, 04 Feb 2016 13:40:38 +0100 |
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On Wednesday 03 February 2016 14:15:28 Andrzej Hajda wrote: > diff --git a/include/linux/err.h b/include/linux/err.h > index 56762ab..b7d4a9f 100644 > --- a/include/linux/err.h > +++ b/include/linux/err.h > @@ -18,7 +18,9 @@ > > #ifndef __ASSEMBLY__ > > -#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO) > +#define IS_ERR_VALUE(x) ((typeof(x))(-1) <= 0 \ > + ? unlikely((x) <= -1) \ > + : unlikely((x) >= (typeof(x))-MAX_ERRNO)) > > static inline void * __must_check ERR_PTR(long error) > { >
This has caused a warning to reappear that I had fixed before:
fs/gfs2/dir.c: In function 'get_first_leaf': fs/gfs2/dir.c:802:9: warning: 'leaf_no' may be used uninitialized in this function [-Wmaybe-uninitialized] error = get_leaf(dip, leaf_no, bh_out); ^ fs/gfs2/dir.c: In function 'dir_split_leaf': fs/gfs2/dir.c:1021:8: warning: 'leaf_no' may be used uninitialized in this function [-Wmaybe-uninitialized] error = get_leaf(dip, leaf_no, &obh);
See my original patch that was applied at http://www.gossamer-threads.com/lists/linux/kernel/2353964
Apparently the new version is complex enough to prevent gcc from doing some optimizations it should do.
I have tried to come up with a new variant that does not bring the warning back and that should work in all cases:
diff --git a/include/linux/err.h b/include/linux/err.h index b7d4a9ff6342..bd4936a2c352 100644 --- a/include/linux/err.h +++ b/include/linux/err.h @@ -18,9 +18,7 @@ #ifndef __ASSEMBLY__ -#define IS_ERR_VALUE(x) ((typeof(x))(-1) <= 0 \ - ? unlikely((x) <= -1) \ - : unlikely((x) >= (typeof(x))-MAX_ERRNO)) +#define IS_ERR_VALUE(x) (unlikely((unsigned long long)(x) >= (unsigned long long)(typeof(x))-MAX_ERRNO)) static inline void * __must_check ERR_PTR(long error) {
I'm not sure if the cast to 'unsigned long long' might cause less efficient code to be generated by gcc. I would hope that it is smart enough to not actually extend shorter variables to 64 bit before doing the comparison but I have not checked yet.
Arnd
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