linux-hardening - Re: [PATCH][next] xfs: Fix fall-through warnings for Clang

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Date:   Wed, 26 May 2021 13:21:06 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     "Darrick J. Wong" <djwong@...nel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH][next] xfs: Fix fall-through warnings for Clang



On 4/20/21 18:56, Gustavo A. R. Silva wrote:
> 
> 
> On 4/20/21 18:38, Darrick J. Wong wrote:
>> On Tue, Apr 20, 2021 at 06:06:52PM -0500, Gustavo A. R. Silva wrote:
>>> In preparation to enable -Wimplicit-fallthrough for Clang, fix
>>> the following warnings by replacing /* fall through */ comments,
>>> and its variants, with the new pseudo-keyword macro fallthrough:
>>>
>>> fs/xfs/libxfs/xfs_alloc.c:3167:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/libxfs/xfs_da_btree.c:286:3: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/libxfs/xfs_ag_resv.c:346:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/libxfs/xfs_ag_resv.c:388:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/xfs_bmap_util.c:246:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/xfs_export.c:88:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/xfs_export.c:96:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/xfs_file.c:867:3: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/xfs_ioctl.c:562:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/xfs_ioctl.c:1548:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/xfs_iomap.c:1040:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/xfs_inode.c:852:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/xfs_log.c:2627:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/xfs_trans_buf.c:298:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/scrub/bmap.c:275:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/scrub/btree.c:48:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/scrub/common.c:85:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/scrub/common.c:138:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/scrub/common.c:698:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/scrub/dabtree.c:51:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>> fs/xfs/scrub/repair.c:951:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
>>>
>>> Notice that Clang doesn't recognize /* fall through */ comments as
>>> implicit fall-through markings, so in order to globally enable
>>> -Wimplicit-fallthrough for Clang, these comments need to be
>>> replaced with fallthrough; in the whole codebase.
>>>
>>> Link: https://github.com/KSPP/linux/issues/115
>>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>>
>> I've already NAKd this twice, so I guess I'll NAK it a third time.
> 
> Darrick,
> 
> The adoption of fallthrough; has been already accepted and in use since Linux v5.7:
> 
> https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through
> 
> This change is needed, and I would really prefer if this goes upstream through your tree.
> 
> Linus has taken these patches directly for a while, now.
> 
> Could you consider taking it this time? :)
> 

Hi Darrick,

If you don't mind, I will take this in my -next[1] branch for v5.14, so we can globally enable
-Wimplicit-fallthrough for Clang in that release.

We had thousands of these warnings and now we are down to 47 in next-20210526,
22 of which are fixed with this patch.

Thanks
--
Gustavo

[1] https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/log/?h=for-next/kspp