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Date: Thu, 14 Apr 2022 17:08:53 +0200
From: Christophe de Dinechin <dinechin@...hat.com>
To: trivial@...nel.org
Cc: Ben Segall <bsegall@...gle.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>, Mel Gorman <mgorman@...e.de>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Jason Wang <jasowang@...hat.com>,
virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org,
Zhen Lei <thunder.leizhen@...wei.com>,
Christophe de Dinechin <dinechin@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 1/3] sched/headers: Fix compilation error with GCC 12
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@...echin.org>
Signed-off-by: Christophe de Dinechin <dinechin@...hat.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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