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Purify
Developer(s)IBM Rational
Stable release
7.0.1 / November 11, 2009
Operating systemWindows, Linux, Solaris, AIX
TypeMemory debugger
LicenseProprietary software
Websiteibm.com

Purify is a memory debugger program used by software developers to detect memory access errors in programs, especially those written in C or C++. It was originally written by Reed Hastings of Pure Software. Pure Software later merged with Atria Software to form Pure Atria Software, which in turn was later acquired by Rational Software, which in turn was acquired by IBM. It is functionally similar to other memory debuggers, such as Insure++, Valgrind and BoundsChecker.

Overview

Purify allows dynamic verification, a process by which a program discovers errors that occur when the program runs, much like a debugger. Static verification or static code analysis, by contrast, involves detecting errors in the source code without ever compiling or running it, just by discovering logical inconsistencies. The type checking by a C compiler is an example of static verification.

When a program is linked with Purify, corrected verification code is automatically inserted into the executable by parsing and adding to the object code, including libraries. That way, if a memory error occurs, the program will print out the exact location of the error, the memory address involved, and other relevant information. Purify also detects memory leaks. By default, a leak report is generated at program exit but can also be generated by calling the Purify leak-detection API from within an instrumented application.

The errors that Purify discovers include array bounds reads and writes, trying to access unallocated memory, freeing unallocated memory (usually due to freeing the same memory for the second time), as well as memory leaks (allocated memory with no pointer reference). Most of these errors are not fatal (at least not at the site of the error), and often when just running the program there is no way to detect them, except by observing that something is wrong due to incorrect program behavior. Hence Purify helps by detecting these errors and telling the programmer exactly where they occur. Because Purify works by instrumenting all the object code, it detects errors that occur inside of third-party or operating system libraries. These errors are often caused by the programmer passing incorrect arguments to the library calls, or by misunderstandings about the protocols for freeing data structures used by the libraries. These are often the most difficult errors to find and fix.

Differences with traditional debuggers

The ability to detect non-fatal errors is a major distinction between Purify and similar programs from the usual debuggers. By contrast, debuggers generally only allow the programmer to quickly find the sources of fatal errors, such as a program crash due to dereferencing a null pointer, but do not help to detect the non-fatal memory errors. Debuggers are useful for other things that Purify is not intended for, such as for stepping through the code line by line or examining the program's memory by hand at a particular moment of execution. In other words, these tools can complement each other for a skilled developer.

Purify also includes other functionality, such as high-performance watchpoints, which are of general use while using a debugger on one's code.

It is worth noting that using Purify makes the most sense in programming languages that leave memory management to the programmer. Hence, in Java, Lisp, or Visual Basic, for example, automatic memory management reduces occurrence of any memory leaks. These languages can however still have leaks; unnecessary references to objects will prevent the memory from being re-allocated. IBM has a product called Rational Application Developer to uncover these sorts of errors.

Supported platforms

Supported C/C++ Platforms
Operating System Processor Architectures Operating System versions Compilers Debuggers Miscellaneous
Solaris
Sun UltraSPARC Solaris 10 base through 5/09
Solaris 9 base through 9/05
Solaris 8 base through 2/04 		Sun C/C++ 5.3 through 5.10
GNU gcc/g++ 4.0 through 4.4
GNU gcc/g++ 3.0 through 3.4 		Sun dbx 7.0 through 7.7
Sun dbx 6.2
GNU gdb 6.0 through 6.7 		Solaris threads
POSIX kernel threads
Solaris ld 5.8 through 5.10
AMD64
Intel 64 		Solaris 10 6/06 through 5/09 Sun C/C++ 5.8 through 5.10
GNU gcc/g++ 4.0 through 4.4
GNU gcc/g++ 3.4 		Sun dbx 7.5 through 7.7
GNU gdb 6.0 through 6.7 		POSIX kernel threads
Solaris ld 5.10
Linux
Intel IA-32 RHEL 5 (Server/Desktop) base through 5.4
RHEL 4 (AS/ES/WS) base through 4.8
RHEL 3 (AS/ES/WS) base through U9
SLES 11 base
SLES 10 base through SP2
SLES 9 base through SP4 		GNU gcc/g++ 4.0 through 4.4
GNU gcc/g++ 3.2 through 3.4
Intel icc 11.0 		GNU gdb 6.0 through 6.8 Native POSIX thread library (NPTL)
GNU ld 2.13 through 2.17
AMD64
Intel 64 		RHEL 5 (Server/Desktop) base through 5.4
RHEL 4 (AS/ES/WS) base through 4.8
SLES 11 base
SLES 10 base through SP2
SLES 9 base through SP4 		GNU gcc/g++ 4.0 through 4.4
GNU gcc/g++ 3.2 through 3.4
Intel icc 11.0 		GNU gdb 6.0 through 6.8 Native POSIX thread library (NPTL)
GNU ld 2.13 through 2.17
AIX
IBM POWER5
IBM POWER6 		AIX 6.1 base through TL3
AIX 5L v5.3 base through TL9
 IBM XL C/C++ 10.1
IBM XL C/C++ 9.0
IBM XL C/C++ 8.0
IBM XL C/C++ 7.0
GNU gcc/g++ 3.4 		IBM Debugger 6.0
IBM Debugger 5.0
GNU gdb 6.2 		POSIX kernel threads
AIX ld 5.2 through 6.1
Windows
Intel IA-32 Vista Business base through SP2
Vista Enterprise base through SP2
Vista Ultimate base through SP2
XP Professional base through SP3
2000 Professional SP2 through SP4
2000 Server SP2 through SP4
2000 Advanced Server SP2 through SP4
Server 2003 Standard base through SP2
Server 2003 Enterprise base through SP2
Server 2003 R2 Standard base through SP2
Server 2003 R2 Enterprise base through SP2
Server 2008 Enterprise Edition base through SP2
Server 2008 Standard Edition base through SP2
Server 2008 DataCenter Edition base through SP2
 Visual Studio 2010
Visual Studio 2008
Visual Studio 2005
Visual Studio .NET 2003
Visual Studio .NET
Visual Studio 6.0
 Visual Studio 2010
Visual Studio 2008
Visual Studio 2005
Visual Studio .NET 2003
Visual Studio .NET
Visual Studio 6.0
Supported Java/.NET Platforms
Platform Data Collection Type Runtime Environment
Windows
Java data collection IBM JRE 1.4.2
IBM JRE 5.0
SUN JRE 1.4.2
SUN JRE 1.5.0
.NET data collection .NET Framework 1.0
.NET Framework 1.1 base through SP1
.NET Framework 2.0
.NET Framework 3.0, 3.5

See also

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