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From:   Kalle Valo <kvalo@codeaurora.org>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Maharaja Kennadyrajan <mkenna@codeaurora.org>,
        "David S. Miller" <davem@davemloft.net>,
        ath10k@lists.infradead.org, linux-wireless@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 2/2] ath10k: fix ath10k_pci struct layout
References: <20200509120707.188595-1-arnd@arndb.de>
        <20200509120707.188595-2-arnd@arndb.de>
Date:   Mon, 11 May 2020 15:05:01 +0300
In-Reply-To: <20200509120707.188595-2-arnd@arndb.de> (Arnd Bergmann's message
        of "Sat, 9 May 2020 14:06:33 +0200")
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Arnd Bergmann <arnd@arndb.de> writes:

> gcc-10 correctly points out a bug with a zero-length array in
> struct ath10k_pci:
>
> drivers/net/wireless/ath/ath10k/ahb.c: In function 'ath10k_ahb_remove':
> drivers/net/wireless/ath/ath10k/ahb.c:30:9: error: array subscript 0
> is outside the bounds of an interior zero-length array 'struct
> ath10k_ahb[0]' [-Werror=zero-length-bounds]
>    30 |  return &((struct ath10k_pci *)ar->drv_priv)->ahb[0];
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In file included from drivers/net/wireless/ath/ath10k/ahb.c:13:
> drivers/net/wireless/ath/ath10k/pci.h:185:20: note: while referencing 'ahb'
>   185 |  struct ath10k_ahb ahb[0];
>       |                    ^~~
>
> The last addition to the struct ignored the comments and added
> new members behind the array that must remain last.
>
> Change it to a flexible-array member and move it last again to
> make it work correctly, prevent the same thing from happening
> again (all compilers warn about flexible-array members in the
> middle of a struct) and get it to build without warnings.

Very good find, thanks! This bug would cause all sort of strange memory
corruption issues.

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