linux-kernel - Re: [PATCH][next] ocfs2: Avoid -Wflex-array-member-not-at-end warning

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Message-ID: <ac62854d-58ff-41be-bf81-6cf783cbdcb8@linux.alibaba.com>
Date: Wed, 3 Dec 2025 13:47:56 +0800
From: Joseph Qi <joseph.qi@...ux.alibaba.com>
To: Heming Zhao <heming.zhao@...e.com>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 akpm <akpm@...ux-foundation.org>
Cc: Mark Fasheh <mark@...heh.com>, Joel Becker <jlbec@...lplan.org>,
 ocfs2-devel@...ts.linux.dev, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] ocfs2: Avoid -Wflex-array-member-not-at-end warning



On 2025/11/17 13:32, Heming Zhao wrote:
> On Tue, Nov 11, 2025 at 12:01:19PM +0900, 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 new TRAILING_OVERLAP() helper to fix the following warning:
>>
>> fs/ocfs2/xattr.c:52:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>>
>> This helper creates a union between a flexible-array member (FAM) and a
>> set of MEMBERS that would otherwise follow it.
>>
>> This overlays the trailing MEMBER struct ocfs2_extent_rec er; onto the
>> FAM struct ocfs2_xattr_value_root::xr_list.l_recs[], while keeping the
>> FAM and the start of MEMBER aligned.
>>
>> The static_assert() ensures this alignment remains, and it's
>> intentionally placed inmediately after the related structure --no
>> blank line in between.
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> 
> LGTM.
> Reviewed-by: Heming Zhao <heming.zhao@...e.com>
> 

Acked-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
>> ---
>>  fs/ocfs2/xattr.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
>> index d70a20d29e3e..09069defd7e1 100644
>> --- a/fs/ocfs2/xattr.c
>> +++ b/fs/ocfs2/xattr.c
>> @@ -49,9 +49,13 @@
>>  #include "ocfs2_trace.h"
>>  
>>  struct ocfs2_xattr_def_value_root {
>> -	struct ocfs2_xattr_value_root	xv;
>> -	struct ocfs2_extent_rec		er;
>> +	/* Must be last as it ends in a flexible-array member. */
>> +	TRAILING_OVERLAP(struct ocfs2_xattr_value_root, xv, xr_list.l_recs,
>> +		struct ocfs2_extent_rec		er;
>> +	);
>>  };
>> +static_assert(offsetof(struct ocfs2_xattr_def_value_root, xv.xr_list.l_recs) ==
>> +	      offsetof(struct ocfs2_xattr_def_value_root, er));
>>  
>>  struct ocfs2_xattr_bucket {
>>  	/* The inode these xattrs are associated with */
>> -- 
>> 2.43.0
>>
>>