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 <hao.a.wu@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/ShellPkg/Application/Shell/ShellParametersProtocol.c b/ShellPkg/Application/Shell/ShellParametersProtocol.c
index 499915521a..8d76fb4be7 100644
--- a/ShellPkg/Application/Shell/ShellParametersProtocol.c
+++ b/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)) {