linux-kernel - Re: [PATCH] treewide: Replace zero-length arrays with flexible-array member

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Date:   Tue, 11 Feb 2020 10:32:29 -0800
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH] treewide: Replace zero-length arrays with flexible-array
 member

On Tue, Feb 11, 2020 at 11:41:26AM -0600, 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
> unadvertenly introduced[3] to the codebase from now on.
> 
> All these instances of code were found with the help of the following
> Coccinelle script:
> 
> @@
> identifier S, member, array;
> type T1, T2;
> @@
> 
> struct S {
>   ...
>   T1 member;
>   T2 array[
> - 0
>   ];
> };
> 
> [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")
> 
> NOTE: I'll carry this in my -next tree for the v5.6 merge window.

Why not carve this up into per-subsystem patches so that we can apply
them to our 5.7-rc1 trees and then you submit the "remaining" that don't
somehow get merged at that timeframe for 5.7-rc2?

thanks,

greg k-h