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Date: Mon, 17 Feb 2020 17:36:11 +0100 From: Jessica Yu <jeyu@...nel.org> To: "Gustavo A. R. Silva" <gustavo@...eddedor.com> Cc: linux-kernel@...r.kernel.org Subject: Re: [PATCH] kernel: module: Replace zero-length array with flexible-array member +++ Gustavo A. R. Silva [13/02/20 09:14 -0600]: >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 <gustavo@...eddedor.com> Applied, thanks Gustavo! Jessica >--- > kernel/module.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > >diff --git a/kernel/module.c b/kernel/module.c >index 33569a01d6e1..b88ec9cd2a7f 100644 >--- a/kernel/module.c >+++ b/kernel/module.c >@@ -1515,7 +1515,7 @@ struct module_sect_attr { > struct module_sect_attrs { > struct attribute_group grp; > unsigned int nsections; >- struct module_sect_attr attrs[0]; >+ struct module_sect_attr attrs[]; > }; > > static ssize_t module_sect_show(struct module_attribute *mattr, >@@ -1608,7 +1608,7 @@ static void remove_sect_attrs(struct module *mod) > struct module_notes_attrs { > struct kobject *dir; > unsigned int notes; >- struct bin_attribute attrs[0]; >+ struct bin_attribute attrs[]; > }; > > static ssize_t module_notes_read(struct file *filp, struct kobject *kobj, >-- >2.25.0 >
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