Background
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no invariant sections, with no cover texts and no back cover texts. We would be grateful to anyone who points out errors and inaccuracies in this document; we will correct it as soon as we are informed.
Introduction
Purpose
Acknowledgments
Copyright and Distribution Policy
Feedback and Corrections
Getting it Installed
Getting Valgrind
Installing
Valgrind works directly with the executable files, without requiring you to recompile, relink, or modify the program to be checked. Valgrind decides whether the program needs to be modified to prevent memory leaks, and also points out where "leaks" occur. For this reason, Valgrind finds errors not only in your application, but also in all supporting dynamically linked (.so format) libraries, including the GNU C library, the X client libraries, Qt if you work with KDE, and so on.
This often includes libraries, for example the GNU C library, which may contain memory access violations. The check can be performed simply by placing the word valgrind just before the normal command used to invoke the program. The output contains the usual output of ps −ax also with the detailed report from valgrind.
A Closer View
Why Valgrind?
Usage
- Invoking Valgrind
- How to Identify the Error from the Error Report
- Types of Errors with Examples
- How to Suppress Errors
This part of the error report says that a read error occurred at line number 7, in the function print. Illegal read/write errors occur when you try to read/write from/to an address that is not in the address range of your program. Here you are trying to read/write from/to address (p+sizeof(int)*11) which is not assigned to the program.
If it's an address that's already freed up, you'll be told that the freebie is invalid. So this is not a problem on Linux, but this program may crash on any other platform. You can't easily fix these, but you don't want to see these errors (and yes, there are many!).
This is useful if part of your project contains errors that you can't or don't want to fix, but you don't want to be constantly reminded of them. Addrn, if it is an address error. (N = size(datatype)) = free, if it's a free error (eg: free disabled).
Limitations and Dependencies of Valgrind
This causes the .so to be loaded as an additional library for any dynamically linked ELF binary executed later, allowing the program to be debugged. The finalization function exits and returns control of the synthetic CPU to the real one. The 'V' bits indicate the validity of the 8 bits in the byte and the 'A' bit indicates the validity of the byte address.
In either of these two situations, if the data turns out to be undefined, an error report will be generated.
Let's Go Deeper
How Valgrind Tracks Validity of Each Byte
All bytes that are in memory but not in the CPU have a valid bit - a), indicating whether the corresponding memory location is accessible by the program. When a call to malloc, new, or any other memory allocation function is made, the 'A' bits corresponding to the allocated bytes are set. When values are loaded from memory, the 'A' bits corresponding to each byte are checked by Valgrind, and if the 'A' bit corresponding to a byte is set, then its 'V' bits are checked.
If the 'V' bits are not set, an error is generated and the 'V' bits are set to indicate validity. Both are due to the access address location p + sizeof(int)*5 not being assigned to the program. Therefore, the uninitialized value does not occur either during the execution of j = p[5] or during the execution of if(p[5]==1).
Cache Profiling
Valgrind can simulate the cache, which means it can show what happens in the cache when a program is running. The cachegrind shell script also produces a file, cachegrind.out, that contains line-by-line cache profiling information that is not human-readable. If the vg_annotate shell script is used without any arguments, it will read the cachegrind.out file and produce output that is human understandable.
When C, C++ or assembly source programs are passed as input to vg_annotate, the number of cache reads, writes, misses, etc. is displayed. Once you understand the basic concept, it's not difficult to take steps on your own.
Concluding Remarks
GNU Free Documentation License
- PREAMBLE
- APPLICABILITY AND DEFINITIONS
- VERBATIM COPYING
- COPYING IN QUANTITY
- MODIFICATIONS
- COMBINING DOCUMENTS
- COLLECTIONS OF DOCUMENTS
- AGGREGATION WITH INDEPENDENT WORKS
- TRANSLATION
- TERMINATION
- FUTURE REVISIONS OF THIS LICENSE
- How to use this License for your documents
This license is a kind of "copyleft", which means that derivative works of the document itself must be free in the same sense. A "modified version" of the Document means any work containing the Document or part thereof, either copied verbatim or with changes and/or translated into another language. A "transparent" copy of the document means a machine-readable copy, represented in a format whose specification is available to the public, the content of which can be viewed and edited directly and.
Copying with limited changes to covers, as long as they preserve the title of the Document and meet these conditions, may be treated as verbatim copying in other respects. List on the title page, as authors, one or more persons or entities responsible for authoring the changes in the Modified Version, together with at least five of the Document's primary authors (all of its primary authors, if there are fewer than five). Enter on the Title page the name of the publisher of the Modified Version as the publisher.
Keep the section titled "History" and its title, and add an item to it that lists at least the title, year, new authors, and publisher of the revised version as listed on the title page. If the document does not have a section titled "History," create one by specifying the title, year, authors, and publisher of the document as listed on its title page, and then add an element describing the modified version as listed in the previous sentence. Keep the network location, if any, listed in the public access document of the transparent copy of the document, as well as the network locations listed in the document for the earlier versions on which it is based.
You can omit a network location for a work that was published at least four years before the document itself, or if the original publisher of the version it refers to gives permission. Keep all the invariant sections of the document unchanged in their text and in their titles. You can add a passage of up to five words as a cover text and a passage of up to 25 words as a back text to the end of the list of cover texts in the modified version.
The author(s) and publisher(s) of the Document do not by this License grant permission to use their names for publicity or to assert or imply approval of any Modified Version. Make the same adjustment to the section headings in the Invariant Sections list in the license notice for the combined work. You may make a collection consisting of the Document and other documents issued under this License and replace the individual copies of this License in different documents with a single copy that is included in the collection, provided that you follow the terms of this License for verbatim copying of each of the documents in all other respects.
34;aggregate", and this license does not apply to other independent works so assembled with the Document, because they are so assembled, if not themselves derivative parts of the Document. A translation is considered a modification of a kind, so you may distribute translations of the Document under with the terms of Section 4.