Re: [PATCH v3 2/6] CryptoPkg: Refine type cast for pointer subtraction

["Long, Qin" <qin.long@intel.com>]

Reviewed-by: Qin Long <qin.long@intel.com>


> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> Hao Wu
> Sent: Saturday, February 25, 2017 12:05 PM
> To: edk2-devel@lists.01.org
> Cc: Wu, Hao A; Ye, Ting; Long, Qin
> Subject: [edk2] [PATCH v3 2/6] CryptoPkg: 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;
> 
> Cc: Qin Long <qin.long@intel.com>
> Cc: Ting Ye <ting.ye@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Hao Wu <hao.a.wu@intel.com>
> Acked-by: Laszlo Ersek <lersek@redhat.com>
> ---
>  CryptoPkg/Library/BaseCryptLib/SysCall/RuntimeMemAllocation.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/CryptoPkg/Library/BaseCryptLib/SysCall/RuntimeMemAllocation.c
> b/CryptoPkg/Library/BaseCryptLib/SysCall/RuntimeMemAllocation.c
> index 19c30dc..feaa371 100644
> --- a/CryptoPkg/Library/BaseCryptLib/SysCall/RuntimeMemAllocation.c
> +++ b/CryptoPkg/Library/BaseCryptLib/SysCall/RuntimeMemAllocation.c
> @@ -2,7 +2,7 @@
>    Light-weight Memory Management Routines for OpenSSL-based Crypto
>    Library at Runtime Phase.
> 
> -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
> @@ -282,7 +282,7 @@ RuntimeFreeMem (
>    UINTN  StartOffset;
>    UINTN  StartPageIndex;
> 
> -  StartOffset    = (UINTN) ((UINT8 *)Buffer - mRTPageTable->DataAreaBase);
> +  StartOffset    = (UINTN)Buffer - (UINTN)mRTPageTable->DataAreaBase;
>    StartPageIndex = RT_SIZE_TO_PAGES (mRTPageTable-
> >Pages[RT_SIZE_TO_PAGES(StartOffset)].StartPageOffset);
> 
>    while (StartPageIndex < mRTPageTable->PageCount) { @@ -403,7 +403,7
> @@ void *realloc (void *ptr, size_t size)
>    //
>    // Get Original Size of ptr
>    //
> -  StartOffset    = (UINTN) ((UINT8 *)ptr - mRTPageTable->DataAreaBase);
> +  StartOffset    = (UINTN)ptr - (UINTN)mRTPageTable->DataAreaBase;
>    StartPageIndex = RT_SIZE_TO_PAGES (mRTPageTable-
> >Pages[RT_SIZE_TO_PAGES (StartOffset)].StartPageOffset);
>    PageCount      = 0;
>    while (StartPageIndex < mRTPageTable->PageCount) {
> --
> 1.9.5.msysgit.0
> 
> _______________________________________________
> edk2-devel mailing list
> edk2-devel@lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel