linux-hardening - [PATCH] scsi: aic94xx: Fix fall-through warning for Clang

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Message-ID: <20210701010433.GA57746@embeddedor>
Date:   Wed, 30 Jun 2021 20:04:33 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: [PATCH] scsi: aic94xx: Fix fall-through warning for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a
warning by explicitly adding a fallthrough; statement.

Notice that this seems to be a Duff device for performance[1]. So,
although the code looks a bit _funny_, I didn't want to refactor
or modify it beyond merely adding a fallthrough marking, which
might be the least disruptive way to fix this issue.

[1] https://www.drdobbs.com/a-reusable-duff-device/184406208

Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
JFYI: We had thousands of these sorts of warnings and now we are down
      to just 7 in linux-next(20210630). This is one of those last
      remaining warnings. :)

 drivers/scsi/aic94xx/aic94xx_sds.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/aic94xx/aic94xx_sds.c b/drivers/scsi/aic94xx/aic94xx_sds.c
index 297a66770260..46815e65f7a4 100644
--- a/drivers/scsi/aic94xx/aic94xx_sds.c
+++ b/drivers/scsi/aic94xx/aic94xx_sds.c
@@ -718,10 +718,12 @@ static void *asd_find_ll_by_id(void * const start, const u8 id0, const u8 id1)
 	do {
 		switch (id1) {
 		default:
-			if (el->id1 == id1)
+			if (el->id1 == id1) {
+			fallthrough;
 		case 0xFF:
 				if (el->id0 == id0)
 					return el;
+			}
 		}
 		el = start + le16_to_cpu(el->next);
 	} while (el != start);
-- 
2.27.0