ShellPkg: 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 <[email protected]>
Acked-by: Laszlo Ersek <[email protected]>
Reviewed-by: Ruiyu Ni <[email protected]>
Reviewed-by: Jaben Carsey <[email protected]>

ShellPkg/Application/Shell/ShellParametersProtocol.c

@@ -5,7 +5,7 @@
   (C) Copyright 2016 Hewlett Packard Enterprise Development LP<BR>
   Copyright (C) 2014, Red Hat, Inc.
   (C) Copyright 2013 Hewlett-Packard Development Company, L.P.<BR>
-  Copyright (c) 2009 - 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2009 - 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
@@ -1034,9 +1034,9 @@ UpdateStdInStdOutStdErr(
   StrnCpyS(CommandLineCopy, StrSize(CommandLineCopy)/sizeof(CHAR16), NewCommandLine, StrLen(NewCommandLine));
 
   if (FirstLocation != CommandLineCopy + StrLen(CommandLineCopy)
-    && ((UINTN)(FirstLocation - CommandLineCopy) < StrLen(NewCommandLine))
+    && (((UINTN)FirstLocation - (UINTN)CommandLineCopy)/sizeof(CHAR16) < StrLen(NewCommandLine))
     ){
-    *(NewCommandLine + (UINTN)(FirstLocation - CommandLineCopy)) = CHAR_NULL;
+    *(NewCommandLine + ((UINTN)FirstLocation - (UINTN)CommandLineCopy)/sizeof(CHAR16)) = CHAR_NULL;
   }
 
   if (!EFI_ERROR(Status)) {

ShellPkg/Library/UefiShellDebug1CommandsLib/DmpStore.c

@@ -364,7 +364,7 @@ AppendSingleVariableToFile (
   //
   // Crc32
   //
-  gBS->CalculateCrc32 (Buffer, (UINTN) (Ptr - Buffer), (UINT32 *) Ptr);
+  gBS->CalculateCrc32 (Buffer, (UINTN) Ptr - (UINTN) Buffer, (UINT32 *) Ptr);
 
   Status = ShellWriteFile (FileHandle, &BufferSize, Buffer);
   FreePool (Buffer);

ShellPkg/Library/UefiShellDebug1CommandsLib/SmbiosView/SmbiosView.c

@@ -2,7 +2,7 @@
   Tools of clarify the content of the smbios table.
 
   (C) Copyright 2015 Hewlett-Packard Development Company, L.P.<BR>
-  Copyright (c) 2005 - 2012, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2005 - 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
@@ -700,7 +700,7 @@ CalculateSmbios64BitStructureCountAndLength (
     //
     // Length = Next structure head - this structure head
     //
-    (*Smbios64TableLength) += (UINTN) (Smbios.Raw - Raw);
+    (*Smbios64TableLength) += ((UINTN) Smbios.Raw - (UINTN) Raw);
     if ((*Smbios64TableLength) > Smbios64EntryPoint->TableMaximumSize) {
     	//
     	// The actual table length exceeds maximum table size,

ShellPkg/Library/UefiShellDriver1CommandsLib/Dh.c

@@ -75,7 +75,7 @@ IsValidGuidString(
        ) {
       Walker++;
     } else {
-      if (*Walker == L'-' && (UINTN)(Walker - PrevWalker) == mGuidDataLen[Index]) {
+      if (*Walker == L'-' && (((UINTN)Walker - (UINTN)PrevWalker) / sizeof (CHAR16)) == mGuidDataLen[Index]) {
         Walker++;
         PrevWalker = Walker;
         Index++;
@@ -85,7 +85,7 @@ IsValidGuidString(
     }
   }
 
-  if ((UINTN)(Walker - PrevWalker) == mGuidDataLen[Index]) {
+  if ((((UINTN)Walker - (UINTN)PrevWalker) / sizeof (CHAR16)) == mGuidDataLen[Index]) {
     return TRUE;
   } else {
     return FALSE;

ShellPkg/Library/UefiShellLevel2CommandsLib/Cd.c

@@ -99,10 +99,10 @@ IsCurrentFileSystem (
 
   Splitter2 = StrStr (Cwd, L":");
 
-  if ((UINTN) (Splitter1 - FullPath) != (UINTN) (Splitter2 - Cwd)) {
+  if (((UINTN) Splitter1 - (UINTN) FullPath) != ((UINTN) Splitter2 - (UINTN) Cwd)) {
     return FALSE;
   } else {
-    if (StrniCmp (FullPath, Cwd, (UINTN) (Splitter1 - FullPath)) == NULL) {
+    if (StrniCmp (FullPath, Cwd, ((UINTN) Splitter1 - (UINTN) FullPath) / sizeof (CHAR16)) == NULL) {
       return TRUE;
     } else {
       return FALSE;