[PATCH 2/2] migration: Define BLK_MIG_BLOCK_SIZE as unsigned long long

From: Peter Maydell <peter.maydell@linaro.org>
To: qemu-devel@nongnu.org
Cc: qemu-block@nongnu.org,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Juan Quintela <quintela@redhat.com>, Fam Zheng <fam@euphon.net>,
	Stefan Hajnoczi <stefanha@redhat.com>
Subject: [PATCH 2/2] migration: Define BLK_MIG_BLOCK_SIZE as unsigned long long
Date: Thu, 21 Jul 2022 12:52:07 +0100	[thread overview]
Message-ID: <20220721115207.729615-3-peter.maydell@linaro.org> (raw)
In-Reply-To: <20220721115207.729615-1-peter.maydell@linaro.org>

When we use BLK_MIG_BLOCK_SIZE in expressions like
block_mig_state.submitted * BLK_MIG_BLOCK_SIZE, this multiplication
is done as 32 bits, because both operands are 32 bits.  Coverity
complains about possible overflows because we then accumulate that
into a 64 bit variable.

Define BLK_MIG_BLOCK_SIZE as unsigned long long using the ULL suffix.
The only two current uses of it with this problem are both in
block_save_pending(), so we could just cast to uint64_t there, but
using the ULL suffix is simpler and ensures that we don't
accidentally introduce new variants of the same issue in future.

Resolves: Coverity CID 1487136, 1487175
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
I haven't tried to analyse the code to see if the multiplications
could ever actually end up overflowing, but I would assume
probably not.

 migration/block.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/migration/block.c b/migration/block.c
index 9e5aae58982..3577c815a94 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -28,7 +28,7 @@
 #include "sysemu/block-backend.h"
 #include "trace.h"
 
-#define BLK_MIG_BLOCK_SIZE           (1 << 20)
+#define BLK_MIG_BLOCK_SIZE           (1ULL << 20)
 #define BDRV_SECTORS_PER_DIRTY_CHUNK (BLK_MIG_BLOCK_SIZE >> BDRV_SECTOR_BITS)
 
 #define BLK_MIG_FLAG_DEVICE_BLOCK       0x01
-- 
2.25.1


