MdeModulePkg: Refine type cast for pointer subtraction

For pointer subtraction, the result is of type "ptrdiff_t". According to
the C11 standard (Committee Draft - April 12, 2011):

"When two pointers are subtracted, both shall point to elements of the
same array object, or one past the last element of the array object; the
result is the difference of the subscripts of the two array elements. The
size of the result is implementation-defined, and its type (a signed
integer type) is ptrdiff_t defined in the <stddef.h> header. If the result
is not representable in an object of that type, the behavior is
undefined."

In our codes, there are cases that the pointer subtraction is not
performed by pointers to elements of the same array object. This might
lead to potential issues, since the behavior is undefined according to C11
standard.

Also, since the size of type "ptrdiff_t" is implementation-defined. Some
static code checkers may warn that the pointer subtraction might underflow
first and then being cast to a bigger size. For example:

UINT8  *Ptr1, *Ptr2;
UINTN  PtrDiff;
...
PtrDiff = (UINTN) (Ptr1 - Ptr2);

The commit will refine the pointer subtraction expressions by casting each
pointer to UINTN first and then perform the subtraction:

PtrDiff = (UINTN) Ptr1 - (UINTN) Ptr2;

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

4 files changed, 11 insertions, 11 deletions

diff --git a/MdeModulePkg/Universal/DebugPortDxe/DebugPort.c b/MdeModulePkg/Universal/DebugPortDxe/DebugPort.c
index 298b6b2da3..dcb623cfeb 100644
--- a/MdeModulePkg/Universal/DebugPortDxe/DebugPort.c
+++ b/MdeModulePkg/Universal/DebugPortDxe/DebugPort.c
@@ -4,7 +4,7 @@
   ALL CODE IN THE SERIALIO STACK MUST BE RE-ENTRANT AND CALLABLE FROM

   INTERRUPT CONTEXT

 

-Copyright (c) 2006 - 2014, Intel Corporation. All rights reserved.<BR>

+Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>

 This program and the accompanying materials

 are licensed and made available under the terms and conditions of the BSD License

 which accompanies this distribution.  The full text of the license may be found at

@@ -569,7 +569,7 @@ DebugPortRead (
     LocalBufferSize = *BufferSize - (BufferPtr - (UINT8 *) Buffer);

   } while (LocalBufferSize != 0 && Timeout > 0);

 

-  *BufferSize = (UINTN) (BufferPtr - (UINT8 *) Buffer);

+  *BufferSize = (UINTN) BufferPtr - (UINTN) Buffer;

 

   return Status;

 }

diff --git a/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWrite.c b/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWrite.c
index 2e3e8c77d1..49e747b901 100644
--- a/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWrite.c
+++ b/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWrite.c
@@ -3,7 +3,7 @@
   These are the common Fault Tolerant Write (FTW) functions that are shared 

   by DXE FTW driver and SMM FTW driver.

 

-Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>

+Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>

 This program and the accompanying materials                          

 are licensed and made available under the terms and conditions of the BSD License         

 which accompanies this distribution.  The full text of the license may be found at        

@@ -373,7 +373,7 @@ FtwWrite (
   //

   // If Record is out of the range of Header, return access denied.

   //

-  if (((UINTN)((UINT8 *) Record - (UINT8 *) Header)) > FTW_WRITE_TOTAL_SIZE (Header->NumberOfWrites - 1, Header->PrivateDataSize)) {

+  if (((UINTN) Record - (UINTN) Header) > FTW_WRITE_TOTAL_SIZE (Header->NumberOfWrites - 1, Header->PrivateDataSize)) {

     return EFI_ACCESS_DENIED;

   }

 

diff --git a/MdeModulePkg/Universal/HiiDatabaseDxe/Image.c b/MdeModulePkg/Universal/HiiDatabaseDxe/Image.c
index 1668828486..e2fa16e6e0 100644
--- a/MdeModulePkg/Universal/HiiDatabaseDxe/Image.c
+++ b/MdeModulePkg/Universal/HiiDatabaseDxe/Image.c
@@ -2,7 +2,7 @@
 Implementation for EFI_HII_IMAGE_PROTOCOL.

 

 

-Copyright (c) 2007 - 2016, Intel Corporation. All rights reserved.<BR>

+Copyright (c) 2007 - 2017, Intel Corporation. All rights reserved.<BR>

 This program and the accompanying materials

 are licensed and made available under the terms and conditions of the BSD License

 which accompanies this distribution.  The full text of the license may be found at

@@ -1124,7 +1124,7 @@ HiiSetImage (
     return EFI_OUT_OF_RESOURCES;

   }

 

-  Part1Size = (UINT32) (UINTN) ((UINT8 *) CurrentImageBlock - (UINT8 *) ImagePackage->ImageBlock);

+  Part1Size = (UINT32) ((UINTN) CurrentImageBlock - (UINTN) ImagePackage->ImageBlock);

   Part2Size = ImagePackage->ImageBlockSize - Part1Size - OldBlockSize;

   CopyMem (ImageBlocks, ImagePackage->ImageBlock, Part1Size);

 

diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
index f5b6a5f93e..b0c7434bae 100644
--- a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
+++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
@@ -16,7 +16,7 @@
   VariableServiceSetVariable() should also check authenticate data to avoid buffer overflow,

   integer overflow. It should also check attribute to avoid authentication bypass.

 

-Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>

+Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>

 (C) Copyright 2015 Hewlett Packard Enterprise Development LP<BR>

 This program and the accompanying materials

 are licensed and made available under the terms and conditions of the BSD License

@@ -1170,7 +1170,7 @@ Reclaim (
   // Install the new variable if it is not NULL.

   //

   if (NewVariable != NULL) {

-    if ((UINTN) (CurrPtr - ValidBuffer) + NewVariableSize > VariableStoreHeader->Size) {

+    if (((UINTN) CurrPtr - (UINTN) ValidBuffer) + NewVariableSize > VariableStoreHeader->Size) {

       //

       // No enough space to store the new variable.

       //

@@ -1211,8 +1211,8 @@ Reclaim (
     // If volatile variable store, just copy valid buffer.

     //

     SetMem ((UINT8 *) (UINTN) VariableBase, VariableStoreHeader->Size, 0xff);

-    CopyMem ((UINT8 *) (UINTN) VariableBase, ValidBuffer, (UINTN) (CurrPtr - ValidBuffer));

-    *LastVariableOffset = (UINTN) (CurrPtr - ValidBuffer);

+    CopyMem ((UINT8 *) (UINTN) VariableBase, ValidBuffer, (UINTN) CurrPtr - (UINTN) ValidBuffer);

+    *LastVariableOffset = (UINTN) CurrPtr - (UINTN) ValidBuffer;

     Status  = EFI_SUCCESS;

   } else {

     //

@@ -1223,7 +1223,7 @@ Reclaim (
               (VARIABLE_STORE_HEADER *) ValidBuffer

               );

     if (!EFI_ERROR (Status)) {

-      *LastVariableOffset = (UINTN) (CurrPtr - ValidBuffer);

+      *LastVariableOffset = (UINTN) CurrPtr - (UINTN) ValidBuffer;

       mVariableModuleGlobal->HwErrVariableTotalSize = HwErrVariableTotalSize;

       mVariableModuleGlobal->CommonVariableTotalSize = CommonVariableTotalSize;

       mVariableModuleGlobal->CommonUserVariableTotalSize = CommonUserVariableTotalSize;