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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Wed, 12 Feb 2020 07:21:12 +0000
Message-ID: <CAKv+Gu_EgbX8r3Vuo5rKDS+WY0wHq4fWhPmZ1NKVAgu-Ybk4pg@mail.gmail.com>
Subject: Re: [PATCH] efi/apple-properties: Replace zero-length array with
 flexible-array member
To:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc:     linux-efi <linux-efi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, 12 Feb 2020 at 00:11, Gustavo A. R. Silva
<gustavo@embeddedor.com> 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
> inadvertenly introduced[3] to the codebase from now on.
>
> 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@embeddedor.com>

Queued in efi/next

Thanks,

> ---
>  drivers/firmware/efi/apple-properties.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/firmware/efi/apple-properties.c b/drivers/firmware/efi/apple-properties.c
> index 0e206c9e0d7a..590c9003f3b4 100644
> --- a/drivers/firmware/efi/apple-properties.c
> +++ b/drivers/firmware/efi/apple-properties.c
> @@ -31,7 +31,7 @@ __setup("dump_apple_properties", dump_properties_enable);
>  struct dev_header {
>         u32 len;
>         u32 prop_count;
> -       struct efi_dev_path path[0];
> +       struct efi_dev_path path[];
>         /*
>          * followed by key/value pairs, each key and value preceded by u32 len,
>          * len includes itself, value may be empty (in which case its len is 4)
> @@ -42,7 +42,7 @@ struct properties_header {
>         u32 len;
>         u32 version;
>         u32 dev_count;
> -       struct dev_header dev_header[0];
> +       struct dev_header dev_header[];
>  };
>
>  static void __init unmarshal_key_value_pairs(struct dev_header *dev_header,
> --
> 2.25.0
>