linux-kernel - Re: [PATCH 3/5][next] uapi: wireless: Avoid -Wflex-array-member-not-at-end warnings

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Message-ID: <e4debfb8fff961e889cf333a95132f5ed6687928.camel@sipsolutions.net>
Date: Wed, 16 Oct 2024 11:06:31 +0200
From: Johannes Berg <johannes@...solutions.net>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH 3/5][next] uapi: wireless: Avoid
 -Wflex-array-member-not-at-end warnings

On Tue, 2024-10-15 at 18:31 -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Address the following warnings by changing the type of the middle struct
> members in various composite structs, which are currently causing trouble,
> from `struct sockaddr` to `struct sockaddr_legacy`. Note that the latter
> struct doesn't contain a flexible-array member.
> 
> include/uapi/linux/wireless.h:751:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/wireless.h:776:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/wireless.h:833:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/wireless.h:857:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/wireless.h:864:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> No binary differences are present after these changes.

I don't see how this works if you introduce "struct sockaddr_legacy" in
a non-UAPI header, but then use it in UAPI?!

Also, userspace might have pointers to it or whatnot, and warn/break if
you change the type?

johannes