Messages in this thread | | | Subject | Re: [PATCH] libbpf: Replace zero-length array with flexible-array | From | Daniel Borkmann <> | Date | Mon, 11 May 2020 17:26:27 +0200 |
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On 5/9/20 9:16 PM, Yonghong Song wrote: > On 5/7/20 11:50 AM, 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> > > I think this is probably for bpf-next. > > Acked-by: Yonghong Song <yhs@fb.com>
Applied, thanks!
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