All of lore.kernel.org
 help / color / mirror / Atom feed
From: Peter Oberparleiter <oberpar@linux.ibm.com>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] gcov: gcc_4_7: Replace zero-length array with flexible-array member
Date: Wed, 26 Feb 2020 14:38:40 +0100	[thread overview]
Message-ID: <47b4c6e3-db25-abf4-1b7b-b85697b802c1@linux.ibm.com> (raw)
In-Reply-To: <20200213152241.GA877@embeddedor>

On 13.02.2020 16:22, 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
> 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@embeddedor.com>

Acked-by: Peter Oberparleiter <oberpar@linux.ibm.com>

Andrew, could you pick this patch up?

> ---
>  kernel/gcov/gcc_4_7.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/gcov/gcc_4_7.c b/kernel/gcov/gcc_4_7.c
> index ec37563674d6..908fdf5098c3 100644
> --- a/kernel/gcov/gcc_4_7.c
> +++ b/kernel/gcov/gcc_4_7.c
> @@ -68,7 +68,7 @@ struct gcov_fn_info {
>  	unsigned int ident;
>  	unsigned int lineno_checksum;
>  	unsigned int cfg_checksum;
> -	struct gcov_ctr_info ctrs[0];
> +	struct gcov_ctr_info ctrs[];
>  };
>  
>  /**
> 


-- 
Peter Oberparleiter
Linux on Z Development - IBM Germany


      reply	other threads:[~2020-02-26 13:38 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-13 15:22 Gustavo A. R. Silva
2020-02-26 13:38 ` Peter Oberparleiter [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=47b4c6e3-db25-abf4-1b7b-b85697b802c1@linux.ibm.com \
    --to=oberpar@linux.ibm.com \
    --cc=akpm@linux-foundation.org \
    --cc=gustavo@embeddedor.com \
    --cc=linux-kernel@vger.kernel.org \
    --subject='Re: [PATCH] gcov: gcc_4_7: Replace zero-length array with flexible-array member' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.