Messages in this thread | | | Date | Thu, 19 Mar 2020 16:47:44 -0700 | From | Ira Weiny <> | Subject | Re: [PATCH][next] nvdimm: nd.h: Replace zero-length array with flexible-array member |
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On Thu, Mar 19, 2020 at 06:09:37PM -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:
"won't" be affected?
My reading of [1] indicates that this change will break the allocation in nd_region_activate() because sizeof() can no longer be used on the base structure?
What am I missing?
Ira
> > "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] > > 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 <gustavo@embeddedor.com> > --- > drivers/nvdimm/nd.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/nvdimm/nd.h b/drivers/nvdimm/nd.h > index c4d69c1cce55..85dbb2a322b9 100644 > --- a/drivers/nvdimm/nd.h > +++ b/drivers/nvdimm/nd.h > @@ -39,7 +39,7 @@ struct nd_region_data { > int ns_count; > int ns_active; > unsigned int hints_shift; > - void __iomem *flush_wpq[0]; > + void __iomem *flush_wpq[]; > }; > > static inline void __iomem *ndrd_get_flush_wpq(struct nd_region_data *ndrd, > @@ -157,7 +157,7 @@ struct nd_region { > struct nd_interleave_set *nd_set; > struct nd_percpu_lane __percpu *lane; > int (*flush)(struct nd_region *nd_region, struct bio *bio); > - struct nd_mapping mapping[0]; > + struct nd_mapping mapping[]; > }; > > struct nd_blk_region { > -- > 2.23.0 >
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