Things to Remember When Developing 64-bit Software

OOO "Program Verification Systems"www.viva64.com

Advantages of 64-bit Software

• You can store all the data right in memory

• Performance boost (when the data format is chosen correctly)

• Additional performance boost due to architectural solutions

• No resources wasted to pass through the WoW64 layer

Who can write ideal,

spherical code?

Differences in Programming

• No differences. C/C++ is a language designed to develop crossplatform applications

• Only the data model is different• But in practice, programs are not

completely crossplatform• A compiled 64-bit program != a correct

64-bit program

What Has Changed?

• Pointer size: 4 bytes -> 8 bytes.• Sizes of types size_t, ptrdiff_t, intptr_t,

uintptr_t, INT_PTR, UINTPTR_T: 4 bytes -> 8 bytes.

• Data alignment. Mind it when serializing structures.

• Array index size.• So few? More than enough for troubles!

From Simple to Complex.Magic Numbers

hFileMapping = CreateFileMapping( (HANDLE) 0xFFFFFFFF, NULL, PAGE_READWRITE, (DWORD) 0, (DWORD) (szBufIm), (LPCTSTR) &FileShareNameMap[0]);

//Number 0xFFFFFFFF is “usigned int”. The fixed code:#define INVALID_HANDLE_VALUE ((HANDLE)(LONG_PTR)-1)

Storing Pointers in a 32-bit Variable

char *ptr = ...;int n = (int) ptr;...ptr = (char *) n;

A very annoying bug.It only occurs when the program is running for

a long time.

The Most Important Thing to Remember with 64-bit Development

• The pointer is not the same thing as int or long. By the way, the long type is different in the data models LP64 and LLP64. It also adds some more confusion.

• Don’t use 32-bit types and address arithmetic together. Use these types:– size_t– ptrdiff_t– intptr_t– uintptr_t– INT_PTR, ….

A More Creative Solution for Pointer Storage

int *p1, *p2;....char str[128];sprintf(str, "%X %X", p1, p2);

int *p1, *p2;sscanf(str, "%X %X", &p1, &p2);

Use “%p” to print pointer values. Also, programmers often incorrectly print size_t variables. “%Iu” should be used for this purpose.

const char *invalidFormat = "%u";size_t value = SIZE_MAX;printf(invalidFormat, value);

A few more words about functions with variable number of arguments

Implicit Type Conversionunsigned n = it->find("ABC");if (n != string::npos) return true;

Address Arithmetic. Signed and Unsigned Types

float p1[100];unsigned x = 5;int y = -1;float *p2 = p1 + 50;

p2 = p2 + x * y;

// Access violation*p2 = 1.0f;

Correct code!!!!!!!!!!!!!!!!!!!!!!!!!!

Address Arithmetic. Overflows.

extern int Width, Height, Depth;size_t GetIndex(int x, int y, int z) { return z * Width * Height + y * Width + x;}...MyArray[GetIndex(x, y, z)] = 0.0f;

return size_t(z) * Width * Height + size_t(y) * Width + x;

These errors reveal themselves only at LARGE data amounts. Unit tests won’t help you here, neither will dynamic analyzers such as Bounds Checker (it is too slow).

Incorrect Solutionsreturn size_t(z * Width * Height + y * Width + x);

return size_t(z) * Width * Height + y * Width + x;

Infinite LoopsP.S. The funny thing is that infinite loops sometimes fail to occur – thanks to compiler-performed optimization.

Obsolete typedef and #ifdef

#ifdef _MY_BUILD_32 // Win32 const unsigned BufferSize = 1024*1024;#else // Win16 const unsigned BufferSize = 16*1024;#endif

// A do-it-yourself thing in one filetypedef unsigned UINT_PTR;

Exotic Issues: Buffer Overflow

Structure Size Growthstruct MyStruct{ bool m_bool; char *m_pointer; int m_int;};

struct MyStructOpt{ char *m_pointer; int m_int; bool m_bool;};

Other Issues

• Use of deprecated functions (SetClassLong, GetClassLong, GetFileSize, EnumProcessModules, GlobalMemoryStatus)

• Undeclared functions in C• Different parameters of virtual functions• Array type change• Pointers in unions• Exceptions• And so on…

How to Prepare a Reliable 64-bit Version of a Product?

• Unit-tests (but don’t rely solely on them)• Regression tests• Compiler warning elimination• Using specialized tools, for example the Viva64

rule set included into the PVS-Studio static analyzer.

PVS-Studio• Rule sets:– The most powerful analysis for 64-bit errors among other similar tools– General diagnostics– Micro optimizations– OpenMP

• About the tool:http://www.viva64.com/en/pvs-studio/

• Download:http://www.viva64.com/en/pvs-studio-download/

Visual Studio Integration

C++Builder Integration

References

• Lessons on development of 64-bit C/C++ applications. http://www.viva64.com/en/l/

• An article. A Collection of Examples of 64-bit Errors in Real Programs. http://www.viva64.com/en/a/0065

• Article reviews http://www.viva64.com/en/r/tag/x64/

• Knowledge base http://www.viva64.com/en/k/