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Date: Wed, 12 Feb 2020 21:49:47 +0100 From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com> To: "Gustavo A. R. Silva" <gustavo@...eddedor.com> Cc: linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] auxdisplay: charlcd: replace zero-length array with flexible-array member Hi Gustavo, On Wed, Feb 12, 2020 at 8:49 PM Gustavo A. R. Silva <gustavo@...eddedor.com> 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 > inadvertenly introduced[3] to the codebase from now on. s:inadvertenly:inadvertently: > 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] > > 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@...eddedor.com> I saw the discussion regarding this -- thanks! Do you want me to handle this or will you push everything centrally? If the latter, have my Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com> Cheers, Miguel
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