Messages in this thread Patch in this message | | | From | Christophe de Dinechin <> | Subject | [PATCH 1/3] sched/headers: Fix compilation error with GCC 12 | Date | Thu, 14 Apr 2022 17:08:53 +0200 |
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With gcc version 12.0.1 20220401 (Red Hat 12.0.1-0) (GCC), the following errors are reported in sched.h when building after `make defconfig`:
| CC kernel/sched/core.o | In file included from kernel/sched/core.c:81: | kernel/sched/core.c: In function ‘set_rq_online.part.0’: | kernel/sched/sched.h:2197:52: error: array subscript -1 is outside | array bounds of ‘struct sched_class[44343134792571037]’ | [-Werror=array-bounds] | 2197 | #define sched_class_lowest (__begin_sched_classes - 1) | | ^ | kernel/sched/sched.h:2200:41: note: in definition of macro | ‘for_class_range’ | 2200 | for (class = (_from); class != (_to); class--) | | ^~~ | kernel/sched/sched.h:2203:53: note: in expansion of macro | ‘sched_class_lowest’ | 2203 |for_class_range(class, sched_class_highest, sched_class_lowest) | | ^~~~~~~~~~~~~~~~~~ | kernel/sched/core.c:9115:17: note: in expansion of macro | ‘for_each_class’ | 9115 | for_each_class(class) { | | ^~~~~~~~~~~~~~ | kernel/sched/sched.h:2193:27: note: at offset -208 into object | ‘__begin_sched_classes’ of size [0, 9223372036854775807] | 2193 | extern struct sched_class __begin_sched_classes[]; | | ^~~~~~~~~~~~~~~~~~~~~ | kernel/sched/core.c: In function ‘set_rq_offline.part.0’: | kernel/sched/sched.h:2197:52: error: array subscript -1 is outside | array bounds of ‘struct sched_class[44343134792571037]’ | [-Werror=array-bounds] | 2197 | #define sched_class_lowest (__begin_sched_classes - 1) | | ^ | kernel/sched/sched.h:2200:41: note: in definition of macro | ‘for_class_range’ | 2200 | for (class = (_from); class != (_to); class--) | | ^~~ | kernel/sched/sched.h:2203:53: note: in expansion of macro | ‘sched_class_lowest’ | 2203 |for_class_range(class, sched_class_highest, sched_class_lowest) | | ^~~~~~~~~~~~~~~~~~ | kernel/sched/core.c:9127:17: note: in expansion of macro | ‘for_each_class’ | 9127 | for_each_class(class) { | | ^~~~~~~~~~~~~~ | kernel/sched/sched.h:2193:27: note: at offset -208 into object | ‘__begin_sched_classes’ of size [0, 9223372036854775807] | 2193 | extern struct sched_class __begin_sched_classes[]; | | ^~~~~~~~~~~~~~~~~~~~~ | In function ‘__pick_next_task’, | inlined from ‘pick_next_task’ at kernel/sched/core.c:6204:9, | inlined from ‘__schedule’ at kernel/sched/core.c:6352:9: | kernel/sched/sched.h:2197:52: error: array subscript -1 is outside | array bounds of ‘struct sched_class[44343134792571037]’ | [-Werror=array-bounds] | 2197 | #define sched_class_lowest (__begin_sched_classes - 1) | | ^ | kernel/sched/sched.h:2200:41: note: in definition of macro | ‘for_class_range’ | 2200 | for (class = (_from); class != (_to); class--) | | ^~~ | kernel/sched/sched.h:2203:53: note: in expansion of macro | ‘sched_class_lowest’ | 2203 |for_class_range(class, sched_class_highest, sched_class_lowest) | | ^~~~~~~~~~~~~~~~~~ | kernel/sched/core.c:5711:9: note: in expansion of macro | ‘for_each_class’ | 5711 | for_each_class(class) { | | ^~~~~~~~~~~~~~ | kernel/sched/sched.h: In function ‘__schedule’: | kernel/sched/sched.h:2193:27: note: at offset -208 into object | ‘__begin_sched_classes’ of size [0, 9223372036854775807] | 2193 | extern struct sched_class __begin_sched_classes[]; | | ^~~~~~~~~~~~~~~~~~~~~ | cc1: all warnings being treated as errors
Rewrite the definitions of sched_class_highest and for_class_range to avoid this error as follows:
1/ The sched_class_highest is rewritten to be relative to __begin_sched_classes, so that GCC sees it as being part of the __begin_sched_classes array and not a distinct __end_sched_classes array.
2/ The for_class_range macro is modified to replace the comparison with an out-of-bound pointer __begin_sched_classes - 1 with an equivalent, but in-bounds comparison.
In that specific case, I believe that the GCC analysis is correct and potentially valuable for other arrays, so it makes sense to keep it enabled.
Signed-off-by: Christophe de Dinechin <christophe@dinechin.org> Signed-off-by: Christophe de Dinechin <dinechin@redhat.com> --- kernel/sched/sched.h | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 8dccb34eb190..6350fbc7418d 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2193,11 +2193,18 @@ const struct sched_class name##_sched_class \ extern struct sched_class __begin_sched_classes[]; extern struct sched_class __end_sched_classes[]; -#define sched_class_highest (__end_sched_classes - 1) +/* + * sched_class_highests is really __end_sched_classes - 1, but written in a way + * that makes it clear that it is within __begin_sched_classes[] and not outside + * of __end_sched_classes[]. + */ +#define sched_class_highest (__begin_sched_classes + \ + (__end_sched_classes - __begin_sched_classes - 1)) #define sched_class_lowest (__begin_sched_classes - 1) +/* The + 1 below places the pointers within the range of their array */ #define for_class_range(class, _from, _to) \ - for (class = (_from); class != (_to); class--) + for (class = (_from); class + 1 != (_to) + 1; class--) #define for_each_class(class) \ for_class_range(class, sched_class_highest, sched_class_lowest) -- 2.35.1
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