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authorGustavo A. R. Silva <gustavoars@kernel.org>2020-05-07 13:58:04 -0500
committerPeter Zijlstra <peterz@infradead.org>2020-05-19 20:34:18 +0200
commitdb78538c75e49c09b002a2cd96a19ae0c39be771 (patch)
treee728d72971ab7f6bb4c0735d16475b7f80971cd3 /kernel/locking
parent23b5ae2e8e1326c91b5dfdbb6ebcd5a6820074ae (diff)
downloadlinux-db78538c75e49c09b002a2cd96a19ae0c39be771.tar.bz2
locking/lockdep: Replace zero-length array with flexible-array
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: Gustavo A. R. Silva <gustavoars@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200507185804.GA15036@embeddedor
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/lockdep.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index ac10db66cc63..cfdff122905b 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -489,7 +489,7 @@ struct lock_trace {
struct hlist_node hash_entry;
u32 hash;
u32 nr_entries;
- unsigned long entries[0] __aligned(sizeof(unsigned long));
+ unsigned long entries[] __aligned(sizeof(unsigned long));
};
#define LOCK_TRACE_SIZE_IN_LONGS \
(sizeof(struct lock_trace) / sizeof(unsigned long))