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Date: Thu, 7 May 2020 13:52:24 -0500 From: "Gustavo A. R. Silva" <gustavoars@...nel.org> To: Michał Mirosław <mirq-linux@...e.qmqm.pl> Cc: linux-kernel@...r.kernel.org Subject: [PATCH] cb710: 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@...nel.org> --- include/linux/cb710.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/cb710.h b/include/linux/cb710.h index 60de3fedd3a7..405657a9a0d5 100644 --- a/include/linux/cb710.h +++ b/include/linux/cb710.h @@ -36,7 +36,7 @@ struct cb710_chip { unsigned slot_mask; unsigned slots; spinlock_t irq_lock; - struct cb710_slot slot[0]; + struct cb710_slot slot[]; }; /* NOTE: cb710_chip.slots is modified only during device init/exit and
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