Re: [PATCH v1 17/19] ArmPlatformPkg: Fix UART divisor warning

["Alexei Fedorov" <Alexei.Fedorov@arm.com>]

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Reviewed-by: Alexei Fedorov <Alexei.Fedorov@arm.com>


Alexei

________________________________
From: Sami Mujawar <sami.mujawar@arm.com>
Sent: 23 August 2019 11:55
To: devel@edk2.groups.io <devel@edk2.groups.io>
Cc: Sami Mujawar <Sami.Mujawar@arm.com>; Alexei Fedorov <Alexei.Fedorov@arm.com>; ard.biesheuvel@linaro.org <ard.biesheuvel@linaro.org>; leif.lindholm@linaro.org <leif.lindholm@linaro.org>; Matteo Carlini <Matteo.Carlini@arm.com>; nd <nd@arm.com>
Subject: [PATCH v1 17/19] ArmPlatformPkg: Fix UART divisor warning

The VS2017 compiler reports 'warning C4244: '=': conversion
from 'UINT64' to 'UINT32', possible loss of data' for the
calculation of the UART Divisor value.

Fix this warning by adding appropriate typecast and a validation
that ensures that the UART divisor value generated does not exceed
MAX_UINT32.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
---
 ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c b/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c
index 801990d9551a638c17d560d4226137b8a3ee47bb..2d3c279cce49304959953ec4a34b50e09a7d0045 100644
--- a/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c
+++ b/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c
@@ -2,7 +2,7 @@
   Serial I/O Port library functions with no library constructor/destructor

   Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR>
-  Copyright (c) 2011 - 2016, ARM Ltd. All rights reserved.<BR>
+  Copyright (c) 2011 - 2019, ARM Ltd. All rights reserved.<BR>

   SPDX-License-Identifier: BSD-2-Clause-Patent

@@ -78,6 +78,7 @@ PL011UartInitializePort (
   UINT32      Integer;
   UINT32      Fractional;
   UINT32      HardwareFifoDepth;
+  UINT64      DivisorValue;

   HardwareFifoDepth = (PL011_UARTPID2_VER (MmioRead32 (UartBase + UARTPID2)) \
                        > PL011_VER_R1P4) \
@@ -188,7 +189,12 @@ PL011UartInitializePort (
       return RETURN_INVALID_PARAMETER;
     }

-    Divisor = (UartClkInHz * 4) / *BaudRate;
+    DivisorValue = (((UINT64)UartClkInHz * 4) / *BaudRate);
+    if (DivisorValue > MAX_UINT32) {
+      return RETURN_INVALID_PARAMETER;
+    }
+
+    Divisor = (UINT32)DivisorValue;
     Integer = Divisor >> FRACTION_PART_SIZE_IN_BITS;
     Fractional = Divisor & FRACTION_PART_MASK;
   }
--
'Guid(CE165669-3EF3-493F-B85D-6190EE5B9759)'


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