Messages in this thread | | | Date | Fri, 8 May 2020 15:06:43 +0200 | From | Michał Mirosław <> | Subject | Re: [PATCH] cb710: Replace zero-length array with flexible-array |
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On Thu, May 07, 2020 at 01:52:24PM -0500, Gustavo A. R. Silva wrote: > 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> > --- > 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 >
Acked-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
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