linux-kernel - Re: [PATCH][next] jbd2: Avoid dozens of -Wflex-array-member-not-at-end warnings

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Message-ID: <20241031123313.dfcuttwzzs5f5i7a@quack3>
Date: Thu, 31 Oct 2024 13:33:13 +0100
From: Jan Kara <jack@...e.cz>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.com>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] jbd2: Avoid dozens of
 -Wflex-array-member-not-at-end warnings

On Fri 25-10-24 13:32:58, 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.
> 
> Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
> a flexible structure (`struct shash_desc`) where the size of the
> flexible-array member (`__ctx`) is known at compile-time, and
> refactor the rest of the code, accordingly.
> 
> So, with this, fix 77 of the following warnings:
> 
> include/linux/jbd2.h:1800:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  include/linux/jbd2.h | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 8aef9bb6ad57..ce4560e62d3b 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1796,22 +1796,19 @@ static inline unsigned long jbd2_log_space_left(journal_t *journal)
>  static inline u32 jbd2_chksum(journal_t *journal, u32 crc,
>  			      const void *address, unsigned int length)
>  {
> -	struct {
> -		struct shash_desc shash;
> -		char ctx[JBD_MAX_CHECKSUM_SIZE];
> -	} desc;
> +	DEFINE_RAW_FLEX(struct shash_desc, desc, __ctx, 1);

Am I missing some magic here or the 1 above should be
JBD_MAX_CHECKSUM_SIZE?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR