From 8695e0b1b964f6d7caee667f14dceb7e8a4a3b3c Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Thu, 7 May 2020 13:53:29 -0500 Subject: [PATCH] i2c: mux: Replace zero-length array with flexible-array 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 Reviewed-by: Peter Rosin Signed-off-by: Wolfram Sang --- include/linux/i2c-mux.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/i2c-mux.h b/include/linux/i2c-mux.h index c5a977320f82..98ef73b7c8fd 100644 --- a/include/linux/i2c-mux.h +++ b/include/linux/i2c-mux.h @@ -29,7 +29,7 @@ struct i2c_mux_core { int num_adapters; int max_adapters; - struct i2c_adapter *adapter[0]; + struct i2c_adapter *adapter[]; }; struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,