MdeModulePkg: Refine casting expression result to bigger size

There are cases that the operands of an expression are all with rank less
than UINT64/INT64 and the result of the expression is explicitly cast to
UINT64/INT64 to fit the target size.

An example will be:
UINT32 a,b;
// a and b can be any unsigned int type with rank less than UINT64, like
// UINT8, UINT16, etc.
UINT64 c;
c = (UINT64) (a + b);

Some static code checkers may warn that the expression result might
overflow within the rank of "int" (integer promotions) and the result is
then cast to a bigger size.

The commit refines codes by the following rules:
1). When the expression is possible to overflow the range of unsigned int/
int:
c = (UINT64)a + b;

2). When the expression will not overflow within the rank of "int", remove
the explicit type casts:
c = a + b;

3). When the expression will be cast to pointer of possible greater size:
UINT32 a,b;
VOID *c;
c = (VOID *)(UINTN)(a + b); --> c = (VOID *)((UINTN)a + b);

4). When one side of a comparison expression contains only operands with
rank less than UINT32:
UINT8 a;
UINT16 b;
UINTN c;
if ((UINTN)(a + b) > c) {...} --> if (((UINT32)a + b) > c) {...}

For rule 4), if we remove the 'UINTN' type cast like:
if (a + b > c) {...}
The VS compiler will complain with warning C4018 (signed/unsigned
mismatch, level 3 warning) due to promoting 'a + b' to type 'int'.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
index b0c7434..0a325de 100644
--- a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
+++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
@@ -3754,8 +3754,8 @@ InitNonVolatileVariableStore (
     return EFI_VOLUME_CORRUPTED;

   }

 

-  VariableStoreBase = (EFI_PHYSICAL_ADDRESS) ((UINTN) FvHeader + FvHeader->HeaderLength);

-  VariableStoreLength = (UINT64) (NvStorageSize - FvHeader->HeaderLength);

+  VariableStoreBase = (UINTN) FvHeader + FvHeader->HeaderLength;

+  VariableStoreLength = NvStorageSize - FvHeader->HeaderLength;

 

   mNvFvHeaderCache = FvHeader;

   mVariableModuleGlobal->VariableGlobal.NonVolatileVariableBase = VariableStoreBase;

@@ -4099,7 +4099,7 @@ VariableCommonInitialize (
   GuidHob = GetFirstGuidHob (VariableGuid);

   if (GuidHob != NULL) {

     VariableStoreHeader = GET_GUID_HOB_DATA (GuidHob);

-    VariableStoreLength = (UINT64) (GuidHob->Header.HobLength - sizeof (EFI_HOB_GUID_TYPE));

+    VariableStoreLength = GuidHob->Header.HobLength - sizeof (EFI_HOB_GUID_TYPE);

     if (GetVariableStoreStatus (VariableStoreHeader) == EfiValid) {

       mVariableModuleGlobal->VariableGlobal.HobVariableBase = (EFI_PHYSICAL_ADDRESS) (UINTN) AllocateRuntimeCopyPool ((UINTN) VariableStoreLength, (VOID *) VariableStoreHeader);

       if (mVariableModuleGlobal->VariableGlobal.HobVariableBase == 0) {