From: Gustavo A. R. Silva Date: Thu, 13 Feb 2020 00:14:01 +0000 (-0600) Subject: iommu/qcom: Replace zero-length array with flexible-array member X-Git-Tag: v5.7-rc1~46^2^3 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e26060e1d47a535e0bc41a00708b79bc52dc9fb3;p=thirdparty%2Fkernel%2Flinux.git iommu/qcom: Replace zero-length array with flexible-array member 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] 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 Signed-off-by: Joerg Roedel --- diff --git a/drivers/iommu/qcom_iommu.c b/drivers/iommu/qcom_iommu.c index 4328da0b0a9fd..f6117726da992 100644 --- a/drivers/iommu/qcom_iommu.c +++ b/drivers/iommu/qcom_iommu.c @@ -48,7 +48,7 @@ struct qcom_iommu_dev { void __iomem *local_base; u32 sec_id; u8 num_ctxs; - struct qcom_iommu_ctx *ctxs[0]; /* indexed by asid-1 */ + struct qcom_iommu_ctx *ctxs[]; /* indexed by asid-1 */ }; struct qcom_iommu_ctx {