linux-kernel - [PATCH v3] [SCSI] scsi_debug: silence GCC warning

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Date:	Wed, 17 Jul 2013 09:36:24 +0200
From:	Paul Bolle <pebolle@...cali.nl>
To:	"James E.J. Bottomley" <JBottomley@...allels.com>
Cc:	Akinobu Mita <akinobu.mita@...il.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Douglas Gilbert <dgilbert@...erlog.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3] [SCSI] scsi_debug: silence GCC warning

Building scsi_debug.o triggers a GCC warning:
    drivers/scsi/scsi_debug.c: In function ‘dif_verify’:
    drivers/scsi/scsi_debug.c:1755:3: warning: ‘csum’ may be used uninitialized in this function [-Wmaybe-uninitialized]

This warning was apparently introduced (in v3.11-rc1) by commit
beb40ea42b ("[SCSI] scsi_debug: reduce duplication between
prot_verify_read and prot_verify_write"). It is a false positive. But if
we transform the switch statement in dif_compute_csum() to a
straightforward if/else statement we supply GCC with enough information
to determine that csum will not be used uninitialized.

Signed-off-by: Paul Bolle <pebolle@...cali.nl>
---
0) v2: much simpler, and doesn't change any behavior;
   v3: mention commit bebe40ea42b, as Akinobu suggested.

1) Still only compile tested.

 drivers/scsi/scsi_debug.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index cb4fefa..7565ec5 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -1735,14 +1735,11 @@ static u16 dif_compute_csum(const void *buf, int len)
 {
 	u16 csum;
 
-	switch (scsi_debug_guard) {
-	case 1:
+	if (scsi_debug_guard == 1)
 		csum = ip_compute_csum(buf, len);
-		break;
-	case 0:
+	else
 		csum = cpu_to_be16(crc_t10dif(buf, len));
-		break;
-	}
+
 	return csum;
 }
 
-- 
1.8.1.4

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