From: zhuguangqing <[email protected]>
In commit 04f5c362ec6, a zero-length array cpumask[0] has been
replaced with cpumask[]. But there is still a cpumask[0] in
struct sched_group_capacity{} which maybe missed.
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: zhuguangqing <[email protected]>
---
kernel/sched/sched.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 28709f6b0975..648f02363ff9 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1471,7 +1471,7 @@ struct sched_group_capacity {
int id;
#endif
- unsigned long cpumask[0]; /* Balance mask */
+ unsigned long cpumask[]; /* Balance mask */
};
struct sched_group {
--
2.17.1
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: a3f1d195119ffe62c2c558c6f0dced070c2cf004
Gitweb: https://git.kernel.org/tip/a3f1d195119ffe62c2c558c6f0dced070c2cf004
Author: zhuguangqing <[email protected]>
AuthorDate: Wed, 14 Oct 2020 22:02:20 +08:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Wed, 14 Oct 2020 16:48:48 +02:00
sched: Replace zero-length array with flexible-array
In the following commit:
04f5c362ec6d: ("sched/fair: Replace zero-length array with flexible-array")
a zero-length array cpumask[0] has been replaced with cpumask[].
But there is still a cpumask[0] in 'struct sched_group_capacity'
which was missed.
The point of using [] instead of [0] is that with [] the compiler will
generate a build warning if it isn't the last member of a struct.
[ mingo: Rewrote the changelog. ]
Signed-off-by: zhuguangqing <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
kernel/sched/sched.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 8d1ca65..df80bfc 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1471,7 +1471,7 @@ struct sched_group_capacity {
int id;
#endif
- unsigned long cpumask[0]; /* Balance mask */
+ unsigned long cpumask[]; /* Balance mask */
};
struct sched_group {
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: eba9f08293d76370049ec85581ab3d7f6d069e3e
Gitweb: https://git.kernel.org/tip/eba9f08293d76370049ec85581ab3d7f6d069e3e
Author: zhuguangqing <[email protected]>
AuthorDate: Wed, 14 Oct 2020 22:02:20 +08:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Wed, 14 Oct 2020 19:55:19 +02:00
sched: Replace zero-length array with flexible-array
In the following commit:
04f5c362ec6d: ("sched/fair: Replace zero-length array with flexible-array")
a zero-length array cpumask[0] has been replaced with cpumask[].
But there is still a cpumask[0] in 'struct sched_group_capacity'
which was missed.
The point of using [] instead of [0] is that with [] the compiler will
generate a build warning if it isn't the last member of a struct.
[ mingo: Rewrote the changelog. ]
Signed-off-by: zhuguangqing <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
kernel/sched/sched.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 28709f6..648f023 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1471,7 +1471,7 @@ struct sched_group_capacity {
int id;
#endif
- unsigned long cpumask[0]; /* Balance mask */
+ unsigned long cpumask[]; /* Balance mask */
};
struct sched_group {