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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"[
]>
<article id="Valgrind-HOWTO">
<articleinfo>
<title>Valgrind HOWTO</title>
<authorgroup>
<author>
<firstname>Deepak</firstname>
<surname>P.</surname>
<affiliation>
<address>
<email>pdeepak16@vsnl.com</email>
</address>
</affiliation>
</author>
<author>
<firstname>Sandeep</firstname>
<surname>S.</surname>
<affiliation>
<address>
<email>sandeep_gect@yahoo.com</email>
</address>
</affiliation>
</author>
</authorgroup>
<pubdate>24 August 2002</pubdate>
<revhistory id="revhistory">
<revision>
<revnumber>1.1</revnumber>
<date>2002-09-15</date>
<authorinitials>tab</authorinitials>
<revremark>Converted to XML 4.1.2, added gfdl, reviewed, author revisions</revremark>
</revision>
<revision>
<revnumber>1.0</revnumber>
<date>2002-08-24</date>
<authorinitials>SS</authorinitials>
<revremark>Initial release</revremark>
</revision>
</revhistory>
<abstract>
<para>
This document is a guide to Valgrind, the <function>malloc</function> debugger. Valgrind 1.0.0 is described.
</para>
</abstract>
</articleinfo>
<sect1 id="background">
<title>Background</title>
<para>
Dynamic storage allocation plays an important role in C programming;
it is also the breeding ground of numerous hard-to-track-down bugs.
Freeing an allocated block twice, running off the edge of the
malloc'ed buffer, and failing to keep track of addresses of allocated
blocks are common errors which frustrate the programmer - debugging
them is very difficult due to the errors manifesting themselves
as <quote>mysterious behavior</quote> at places far off from the point where the
programmer actually committed the blunder.
</para>
</sect1>
<sect1 id="intro">
<title>Introduction</title>
<sect2 id="purpose">
<title>Purpose</title>
<para>
Valgrind is an open-source tool for finding memory-management problems
in Linux-x86 executables. It detects memory leaks/corruption in the program
being run. It is being developed by <ulink url="mailto:jseward@acm.org">Julian Seward</ulink>.
</para>
</sect2>
<sect2 id="acknowledgements">
<title>Acknowledgments</title>
<para>
We express our sincere appreciation to Julian Seward
for creating Valgrind. Thanks to Mr.Pramode C.E and also
friends at the Govt Engineering College, Trichur for their advice and cooperation.
</para>
</sect2>
<sect2 id="copyright">
<title>Copyright and Distribution Policy</title>
<para>
Copyright (C)2002 Deepak P, Sandeep S.
</para>
<para>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 Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in <xref linkend="gfdl" /> entitled "GNU
Free Documentation License".</para>
</sect2>
<sect2 id="feedback">
<title>Feedback and Corrections</title>
<para>
Kindly forward feedback and criticism to <ulink url="mailto:pdeepak16@vsnl.com">Deepak.P</ulink> or/and <ulink url="mailto:sandeep_gect@yahoo.com">Sandeep.S</ulink>. We shall be indebted to anybody who points out errors and inaccuracies in this document; we will rectify them as soon as we are informed.
</para>
</sect2>
</sect1>
<sect1 id="getinstalled">
<title>Getting it Installed</title>
<sect2 id="getvalgrind">
<title>Getting Valgrind</title>
<para>
Valgrind may be obtained from the following locations:
<orderedlist>
<listitem><para><ulink url="http://developer.kde.org/~sewardj/" /></para></listitem>
<listitem><para><ulink url="http://freshmeat.net/projects/valgrind/" /></para></listitem>
</orderedlist>
</para>
</sect2>
<sect2 id="installing">
<title>Installing</title>
<para>
Uncompress, compile and install it:
<programlisting>
#tar xvfz valgrind-1.0.0.tar.gz
#cd valgrind-1.0.0
#./configure
#make
#make install
</programlisting>
</para>
<para>
Add the path to your <varname>path</varname> variable. Now valgrind is ready to catch
the bugs.
</para>
</sect2>
</sect1>
<sect1 id="closerview">
<title>A Closer View</title>
<sect2 id="whyvalgrind">
<title>Why Valgrind?</title>
<para>
As said above, memory management is prone to errors that are too
hard to detect. Common errors may be listed as:
</para>
<para>
<orderedlist>
<listitem><para>Use of uninitialized memory</para></listitem>
<listitem><para>Reading/writing memory after it has been freed</para></listitem>
<listitem><para>Reading/writing off the end of malloc'd blocks</para></listitem>
<listitem><para>Reading/writing inappropriate areas on the stack</para></listitem>
<listitem><para>Memory leaks -- where pointers to malloc'd blocks are lost forever</para></listitem>
<listitem><para>Mismatched use of malloc/new/new&lsqb;&rsqb; vs free/delete/delete&lsqb;&rsqb;</para></listitem>
<listitem><para>Some misuses of the POSIX pthreads API</para></listitem>
</orderedlist>
</para>
<para>
These errors usually lead to crashes.
</para>
<para>
This is a situation where we need Valgrind. Valgrind works directly with the
executables, with no need to recompile, relink or modify the program to be
checked. Valgrind decides whether the program should be modified to avoid memory
leak, and also points out the spots of <quote>leak.</quote>
</para>
<para>
Valgrind simulates every single instruction your program executes.
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. That
often includes libraries, for example the GNU C library, which may contain
memory access violations.
</para>
</sect2>
<sect2 id="usage">
<title>Usage</title>
<sect3 id="invoking">
<title>Invoking Valgrind</title>
<para>
The checking may be performed by simply placing the word <command>valgrind</command>
just before the normal command used to invoke the program. For example:
</para>
<screen>
#valgrind ps -ax
</screen>
<para>
Valgrind provides thousands of options. We deliberately avoid them, not
to make this article boring.
</para>
<para>
The output contains the usual output of <command>ps -ax</command> also with the
detailed report by valgrind. Any error (memory related) is pointed out in the error report.
</para>
</sect3>
<sect3 id="erridentify">
<title>How to Identify the Error from the Error Report</title>
<para>
Consider the output of Valgrind for some test program:
<screen>
==1353== Invalid read of size 4
==1353== at 0x80484F6: print (valg_eg.c:7)
==1353== by 0x8048561: main (valg_eg.c:16)
==1353== by 0x4026D177: __libc_start_main
(../sysdeps/generic/libc-start.c :129)
==1353== by 0x80483F1: free@@GLIBC_2.0 (in /home/deepu/valg/a.out)
==1353== Address 0x40C9104C is 0 bytes after a block of size 40
alloc'd
==1353== at 0x40046824: malloc (vg_clientfuncs.c:100)
==1353== by 0x8048524: main (valg_eg.c:12)
==1353== by 0x4026D177: __libc_start_main
(../sysdeps/generic/libc-start.c :129)
==1353== by 0x80483F1: free@@GLIBC_2.0 (in /home/deepu/valg/a.out)
</screen>
</para>
<para>
Here, 1353 is the process ID. This part of the error report says that
a read error has occurred at line number 7, in the function
<function>print</function>. The function <function>print</function> is called by function
<function>main</function>, and both are in the file <filename>valg&lowbar;eg.c</filename>.
The function <function>main</function> is called by the
function <function>&lowbar;&lowbar;libc&lowbar;start&lowbar;main</function> at line
number 129, in <filename>../sysdeps/generic/libc-start.c</filename>.
The function <function>&lowbar;&lowbar;libc&lowbar;start&lowbar;main</function> is called by <function>free@@GLIBC&lowbar;2.0</function> in the file <filename>/home/deepu/valg/a.out.</filename> Similarly details of calling <function>malloc</function> are also given.
</para>
</sect3>
<sect3 id="errortypes">
<title>Types of Errors with Examples</title>
<para>
Valgrind can only really detect two types of errors: use of illegal
address and use of undefined values. Nevertheless, this is enough to
discover all sorts of memory management problems in a program. Some common errors
are given below.
</para>
<sect4 id="uninit-mem">
<title>Use of uninitialized memory</title>
<para>
Sources of uninitialized data are:
</para>
<itemizedlist>
<listitem><para>local variables that have not been initialized.</para></listitem>
<listitem><para>The contents of malloc'd blocks, before writing something there.</para></listitem>
</itemizedlist>
<para>
This is not a problem with <function>calloc</function> since it initializes
each allocated bytes with 0. The <function>new</function> operator in C++ is similar
to <function>malloc</function>. Fields of the created object will be uninitialized.
</para>
<para>
Sample program:
</para>
<programlisting>
#include &lt;stdlib.h&gt;
int main()
{
int p, t;
if (p == 5) /*Error occurs here*/
t = p+1;
return 0;
}
</programlisting>
<para>
Here the value of <literal>p</literal> is uninitialized, therefore <literal>p</literal> may contain
some random value (garbage), so an error may occur at the condition check.
An uninitialized variable will cause error in 2 situations:
</para>
<itemizedlist>
<listitem><para>When it is used to determine the outcome of a conditional branch.
Eg:'if (p == 5)' in the above program.</para></listitem>
<listitem><para>When it is used to generate a memory address.
Eg: In the above program let there be an integer array a&lsqb;10], and if you write 'a&lsqb;p] = 1', it will generate an error.</para></listitem>
</itemizedlist>
</sect4>
<sect4 id="illegal-rw">
<title>Illegal read/write</title>
<para>
Illegal read/write errors occurs when you try to read/write from/to
an address that is not in the address range of your program.
</para>
<para>
Sample program:
</para>
<programlisting>
#include &lt;stdlib.h&gt;
int main()
{
int *p, i, a;
p = malloc(10*sizeof(int));
p[11] = 1; /* invalid write error */
a = p[11]; /* invalid read error */
free(p);
return 0;
}
</programlisting>
<para>
Here you are trying to read/write from/to address (p+sizeof(int)*11)
which is not allocated to the program.
</para>
</sect4>
<sect4 id="invalid-free">
<title>Invalid free</title>
<para>
Valgrind keeps track of blocks allocated to your program with <function>malloc/new</function>. So it can easily check whether argument to free/delete is valid or not.
</para>
<para>
Sample program:
</para>
<programlisting>
#include &lt;stdlib.h&gt;
int main()
{
int *p, i;
p = malloc(10*sizeof(int));
for(i = 0;i &lt; 10;i++)
p[i] = i;
free(p);
free(p); /* Error: p has already been freed */
return 0;
}
</programlisting>
<para>
Valgrind checks the address, which is given as argument to free. If it
is an address that has already been freed you will be told that the free is
invalid.
</para>
</sect4>
<sect4 id="mismatcheduse">
<title>Mismatched Use of Functions</title>
<para>
In C++ you can allocate and free memory using more than one function, but the following rules must be followed:
</para>
<itemizedlist>
<listitem><para>If allocated with <function>malloc</function>, <function>calloc</function>, <function>realloc</function>, <function>valloc</function> or <function>memalign</function>, you must deallocate with <function>free</function>.</para></listitem>
<listitem><para>If allocated with <function>new&lsqb;]</function>, you must deallocate with <function>delete&lsqb;]</function>.</para></listitem>
<listitem><para>If allocated with <function>new</function>, you must deallocate with <function>delete</function>.</para></listitem>
</itemizedlist>
<para>
Sample program:
</para>
<programlisting>
#include &lt;stdlib.h&gt;
int main()
{
int *p, i;
p = ( int* ) malloc(10*sizeof(int));
for(i = 0;i &lt; 10;i++)
p[i] = i;
delete(p); /* Error: function mismatch */
return 0;
}
</programlisting>
<para>
Output by valgrind is:
</para>
<screen>
==1066== ERROR SUMMARY: 1 errors from 1 contexts (suppressed:
0 from 0)
==1066== malloc/free: in use at exit: 0 bytes in 0 blocks.
==1066== malloc/free: 1 allocs, 1 frees, 40 bytes allocated.
==1066== For a detailed leak analysis, rerun with:
--leak-check=yes
==1066== For counts of detected errors, rerun with: -v
</screen>
<para>
>From the above <quote>ERROR SUMMARY</quote> it is clear that there is 0 bytes in 0 blocks
in use at exit, which means that the malloc'd have been freed by
<function>delete</function>. Therefore this is not a problem in Linux, but this program may
crash on some other platform.
</para>
</sect4>
<sect4 id="inv-sys-call-parm">
<title>Errors Occur Due to Invalid System Call Parameter</title>
<para>
Valgrind checks all parameters to system calls.
</para>
<para>
Sample program:
</para>
<para>
<programlisting>
#include &lt;stdlib.h&gt;
#include &lt;unistd.h&gt;
int main()
{
int *p;
p = malloc(10);
read(0, p, 100); /* Error: unaddressable bytes */
free(p);
return 0;
}
</programlisting>
</para>
<para>
<screen>
==1045== Syscall param read(buf) contains unaddressable
byte(s)
==1045== at 0x4032AF44: __libc_read (in
/lib/i686/libc-2.2.2.so)
==1045== by 0x4026D177: __libc_start_main
(../sysdeps/generic/libc-start.c:129)
==1045== by 0x80483E1: read@@GLIBC_2.0 (in
/home/deepu/valg/a.out)
</screen>
</para>
<para>
Here, <literal>buf = p</literal> contains the address of a 10 byte block. The <function>read</function> system call tries to read 100 bytes from standard input and place it at <literal>p</literal>. But the bytes after the first 10 are unaddressable.
</para>
</sect4>
<sect4 id="memleak-detect">
<title>Memory Leak Detection</title>
<para>
Consider the following program:
</para>
<para>
<programlisting>
#include &lt;stdlib.h&gt;
int main()
{
int *p, i;
p = malloc(5*sizeof(int));
for(i = 0;i &lt; 5;i++)
p[i] = i;
return 0;
}
</programlisting>
</para>
<para>
<screen>
==1048== LEAK SUMMARY:
==1048== definitely lost: 20 bytes in 1 blocks.
==1048== possibly lost: 0 bytes in 0 blocks.
==1048== still reachable: 0 bytes in 0 blocks.
</screen>
</para>
<para>
In the above program <literal>p</literal> contains the address of a 20-byte block.
But it is not freed anywhere in the program. So the pointer to this 20
byte block is lost forever. This is known as memory leaking. We can get
the leak summary by using the Valgrind option <option>--leak-check=yes</option>.
</para>
</sect4>
</sect3>
<sect3 id="error-suppress">
<title>How to Suppress Errors</title>
<para>
Valgrind detects numerous problems in many programs which come
pre-installed on your GNU/Linux system. You can't easily fix these, but you don't want to
see these errors (and yes, there are many!). So Valgrind reads a list of errors
to suppress at startup, from a suppression file ending in <filename>.supp</filename>.
</para>
<para>
Suppression files may be modified. This is useful if part of your
project contains errors you can't or don't want to fix, yet you don't want to
continuously be reminded of them. The format of the file is as follows.
</para>
<para>
<programlisting>
{
Error name
Type
fun:function name, which contains the error to suppress
fun:function name, which calls the function specified above
}
</programlisting>
</para>
<para>
<screen>
Error name can be any name.
type=ValueN, if the error is an uninitialized value error.
=AddrN, if it is an address error.(N=sizeof(data type))
=Free, if it is a free error (eg:mismatched free)
=Cond, if error is due to uninitialized CPU condition code.
=Param, if it is an invalid system call parameter error.
</screen>
</para>
<para>
You can then run the program with:
<screen>
valgrind --suppressions=path/to/the/supp_file.supp testprog
</screen>
The output will not contain the errors specified in the suppression file.
</para>
</sect3>
</sect2>
<sect2 id="limitations-deps">
<title>Limitations and Dependencies of Valgrind.</title>
<para>
No software is free from limitations. The same is the case of Valgrind,
however most programs work fine. The limitations are listed below.
</para>
<orderedlist>
<listitem><para> Program runs 25 to 50 times slower.</para></listitem>
<listitem><para>Increased memory consumption.</para></listitem>
<listitem><para>Highly optimized code (compiled with -O1, -O2 options ) may sometimes cheat Valgrind.</para></listitem>
<listitem><para>Valgrind relies on dynamic linking mechanism.</para></listitem>
</orderedlist>
<para>
Valgrind is closely tied to details of the CPU, operating system and to
a less extent, compiler and basic C libraries. Presently Valgrind works only
on the Linux platform (kernels 2.2.X or 2.4.X) on x86s. Glibc 2.1.X or
2.2.X is also required for Valgrind.
</para>
</sect2>
</sect1>
<sect1 id="deeper">
<title>Let's Go Deeper</title>
<para>
Valgrind simulates an Intel x86 processor and runs our test program in
this synthetic processor. The two processors are not exactly same. Valgrind is
compiled into a shared object, valgrind.so. A shell script <literal>valgrind</literal> sets
the <varname>LD&lowbar;PRELOAD</varname> environment variable to point to valgrind.so. This causes the .so to be loaded as an extra library to any subsequently executed
dynamically-linked ELF binary, permitting the program to be debugged.
</para>
<para>
The dynamic linker calls the initialization function of Valgrind. Then the
synthetic CPU takes control from the real CPU. In the memory there may be
some other .so files. The dynamic linker calls the initialization function of
all such .so files. Now the dynamic linker calls the <function>main</function> of the loaded
program. When main returns, the synthetic CPU calls the finalization function of
valgrind.so. During the execution of the finalization function, summary of
all errors detected are printed and memory leaks are checked. Finalization
function exits giving back the control from the synthetic CPU to the real
one.
</para>
<sect2 id="val-validity">
<title>How Valgrind Tracks Validity of Each Byte</title>
<para>
For every byte processed, the synthetic processor maintains 9 bits,
8 'V' bits and 1 'A' bit. The 'V' bits indicate the validity of the 8 bits
in the byte and the 'A' bit indicates validity of the byte address. These
valid-value(V) bits are checked only in two situations:
</para>
<orderedlist>
<listitem><para>when data is used for address generation,</para></listitem>
<listitem><para>when control flow decision is to be made.</para></listitem>
</orderedlist>
<para>
In any of these two situations, if the data is found to be undefined an
error report will be generated. But no error reports are generated while
copying or adding undefined data.
</para>
<para>
However the case with floating-point data is different. During a
floating-point read instruction the 'V' bits corresponding to the data are
checked. Thus copying of uninitialized value will produce error in case of
floating-point numbers.
</para>
<para>
<programlisting>
#include &lt;stdlib.h&gt;
int main()
{
int *p, *a;
p = malloc(10*sizeof(int));
a = malloc(10*sizeof(int));
a[3] = p[3];
free(a);
free(p);
return 0;
}
/* produce no errors */
</programlisting>
</para>
<para>
<programlisting>
#include &lt;stdlib.h&gt;
int main()
{
float *p, *a;
p = malloc(10*sizeof(float));
a = malloc(10*sizeof(float));
a[3] = p[3];
free(a);
free(p);
return 0;
}
/* produces error */
</programlisting>
</para>
<para>
All bytes that are in memory but not in CPU have an associated valid-address(A)
bit, which indicates whether the corresponding memory location is accessible by
the program. When a program starts, the 'A' bits corresponding to each global
variables are set. When a call <function>malloc</function>, <function>new</function> or any other memory allocating function is made, the 'A' bits corresponding to the allocated bytes are
set. Upon freeing the allocated block using <function>free/new/new&lsquo;&rsquo;</function> the
corresponding 'A' bits are cleared. While doing a system call the 'A' bits
are changed appropriately.
</para>
<para>
When values are loaded from memory the 'A' bits corresponding to each
bytes are checked by Valgrind, and if the 'A' bit corresponding to a byte is set
then its 'V' bits is checked. If the 'V' bits are not set, an error will be
generated and the 'V' bits are set to indicate validity. This avoids long chain of
errors. If the 'A' bit corresponding to a loaded byte is 0 then its 'V' bits are
forced to set, despite the value being invalid.
</para>
<para>
Have a look on the following program. Run it.
</para>
<programlisting>
#include &lt;stdlib.h&gt;
int main()
{
int *p, j;
p = malloc(5*sizeof(int));
j = p[5];
if (p[5] == 1)
i = p[5]+1;
free(p);
return 0;
}
</programlisting>
<para>
Here two errors occur. Both of them are due to the accessing address
location <literal> p + sizeof(int)*5 </literal> which is not allocated to the program.
During the execution of <literal>j = p[5]</literal>, since the address <literal> p +
sizeof(int)*5 </literal> is invalid, the 'V' bits of 4 bytes starting at location <literal>p+sizeof(int)*5</literal>
are forced to set. Therefore uninitialized value occurs neither during
the execution of <literal>j = p[5]</literal> nor during the execution of <literal>if(p[5]==1)</literal>.
</para>
</sect2>
<sect2 id="cacheprofiling">
<title>Cache Profiling</title>
<para>
Modern x86 machines use two levels of caching. These levels are L1 and
L2, in which L1 is a split cache that consists of Instruction cache(I1) and
Data cache(D1). L2 is a unified cache.
</para>
<para>
The configuration of a cache means its size, associativity and number
of lines. If the data requested by the processor appears in the upper level
it is called a hit. If the data is not found in the upper level, the
request is called a miss. The lower level in the hierarchy is then accessed to
retrieve the block containing requested data. In modern machines L1 is
first searched for data/instruction requested by the processor. If it is a
hit then that data/instruction is copied to some register in the processor.
Otherwise L2 is searched. If it is a hit then data/instruction is copied to
L1 and from there it is copied to a register. If the request to L2 also is
a miss then main memory has to be accessed.
</para>
<para>
Valgrind can simulate the cache, meaning it can display the things that
occur in the cache when a program is running. For this, first compile your program
with <option>-g</option> option as usual. Then use the shell script <literal>cachegrind</literal> instead of <literal>valgrind</literal>.
</para>
<para>
Sample output:
</para>
<para>
<screen>
==7436== I1 refs: 12,841
==7436== I1 misses: 238
==7436== L2i misses: 237
==7436== I1 miss rate: 1.85%
==7436== L2i miss rate: 1.84%
==7436==
==7436== D refs: 5,914 (4,626 rd + 1,288 wr)
==7436== D1 misses: 357 ( 324 rd + 33 wr)
==7436== L2d misses: 352 ( 319 rd + 33 wr)
==7436== D1 miss rate: 6.0% ( 7.0% + 2.5% )
==7436== L2d miss rate: 5.9% ( 6.8% + 2.5% )
==7436==
==7436== L2 refs: 595 ( 562 rd + 33 wr)
==7436== L2 misses: 589 ( 556 rd + 33 wr)
==7436== L2 miss rate: 3.1% ( 3.1% + 2.5% )
</screen>
</para>
<para>
<screen>
L2i misses means the number of instruction misses that occur in L2
cache.
L2d misses means the number of data misses that occur in L2 cache.
Total number of data references = Number of reads + Number of writes.
Miss rate means fraction of misses that are not found in the upper
level.
</screen>
</para>
<para>
The shell script <literal>cachegrind</literal> also produces a file, <filename>cachegrind.out</filename>, that
contains line-by-line cache profiling information which is not humanly
understandable. A program <literal>vg&lowbar;annotate</literal> can easily interpret this
information. If the shell script <literal>vg&lowbar;annotate</literal> is used without any arguments it will read the file <filename>cachegrind.out</filename> and produce an output which is humanly understandable.
</para>
<para>
When C, C++ or assembly source programs are passed as input to
<literal>vg&lowbar;annotate</literal> it displays the number of cache reads, writes, misses etc.
</para>
<screen>
I1 cache: 16384 B, 32 B, 4-way associative
D1 cache: 16384 B, 32 B, 4-way associative
L2 cache: 262144 B, 32 B, 8-way associative
Command: ./a.out
Events recorded: Ir I1mr I2mr Dr D1mr D2mr Dw D1mw D2mw
Events shown: Ir I1mr I2mr Dr D1mr D2mr Dw D1mw D2mw
Event sort order: Ir I1mr I2mr Dr D1mr D2mr Dw D1mw D2mw
Thresholds: 99 0 0 0 0 0 0 0 0
Include dirs:
User annotated: valg_flo.c
Auto-annotation: off
</screen>
<para>
User-annotated source: <literal>valg&lowbar;flo.c</literal>:
</para>
<programlisting>
Ir I1mr I2mr Dr D1mr D2mr Dw D1mw D2mw
. . . . . . . . . #include&#60;stdlib.h&#62;
. . . . . . . . . int main()
3 1 1 . . . 1 0 0 {
. . . . . . . . . float *p, *a;
6 1 1 . . . 3 0 0 p = malloc(10*sizeof(float));
6 0 0 . . . 3 0 0 a = malloc(10*sizeof(float));
6 1 1 3 1 1 1 1 1 a[3] = p[3];
4 0 0 1 0 0 1 0 0 free(a);
4 0 0 1 0 0 1 0 0 free(p);
2 0 0 2 0 0 . . . }
</programlisting>
<para>
<itemizedlist>
<listitem><para>Ir = Total instruction cache reads.</para></listitem>
<listitem><para>I1mr = I1 cache read misses.</para></listitem>
<listitem><para>I2mr = L2 cache instruction read misses.</para></listitem>
</itemizedlist>
</para>
</sect2>
</sect1>
<sect1 id="conclusion">
<title>Concluding Remarks</title>
<para>
This document has gone through the basics of Valgrind. Once you
understand the basic concept it is not difficult to make steps on your own.
</para>
<para>
If you have found any glaring typos, or outdated info in this document,
please let us know.
</para>
</sect1>
<sect1 id="references">
<title>References</title>
<orderedlist>
<listitem><para><ulink url="http://developer.kde.org/~sewardj/docs/"/></para></listitem>
<listitem><para>The most valuable source of information is the source code itself.</para></listitem>
</orderedlist>
</sect1>
<appendix id="gfdl">
<title>GNU Free Documentation License</title>
<!-- - GNU Project - Free Software Foundation (FSF) -->
<!-- LINK REV="made" HREF="mailto:webmasters@gnu.org" -->
<!-- sect1>
<title>GNU Free Documentation License</title -->
<para>Version 1.1, March 2000</para>
<blockquote>
<para>Copyright (C) 2000 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.</para>
</blockquote>
<sect1 id="gfdl-0">
<title>PREAMBLE</title>
<para>The purpose of this License is to make a manual, textbook,
or other written document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not
being considered responsible for modifications made by
others.</para>
<para>This License is a kind of "copyleft", which means that
derivative works of the document must themselves be free in the
same sense. It complements the GNU General Public License, which
is a copyleft license designed for free software.</para>
<para>We have designed this License in order to use it for manuals
for free software, because free software needs free documentation:
a free program should come with manuals providing the same
freedoms that the software does. But this License is not limited
to software manuals; it can be used for any textual work,
regardless of subject matter or whether it is published as a
printed book. We recommend this License principally for works
whose purpose is instruction or reference.</para>
</sect1>
<sect1 id="gfdl-1">
<title>APPLICABILITY AND DEFINITIONS</title>
<para>This License applies to any manual or other work that
contains a notice placed by the copyright holder saying it can be
distributed under the terms of this License. The "Document",
below, refers to any such manual or work. Any member of the
public is a licensee, and is addressed as "you".</para>
<para>A "Modified Version" of the Document means any work
containing the Document or a portion of it, either copied
verbatim, or with modifications and/or translated into another
language.</para>
<para>A "Secondary Section" is a named appendix or a front-matter
section of the Document that deals exclusively with the
relationship of the publishers or authors of the Document to the
Document's overall subject (or to related matters) and contains
nothing that could fall directly within that overall subject.
(For example, if the Document is in part a textbook of
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The relationship could be a matter of historical connection with
the subject or with related matters, or of legal, commercial,
philosophical, ethical or political position regarding
them.</para>
<para>The "Invariant Sections" are certain Secondary Sections
whose titles are designated, as being those of Invariant Sections,
in the notice that says that the Document is released under this
License.</para>
<para>The "Cover Texts" are certain short passages of text that
are listed, as Front-Cover Texts or Back-Cover Texts, in the
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<para>A "Transparent" copy of the Document means a
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<para>Examples of suitable formats for Transparent copies include
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<para>The "Title Page" means, for a printed book, the title page
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For works in formats which do not have any title page as such,
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</sect1>
<sect1 id="gfdl-2">
<title>VERBATIM COPYING</title>
<para>You may copy and distribute the Document in any medium,
either commercially or noncommercially, provided that this
License, the copyright notices, and the license notice saying this
License applies to the Document are reproduced in all copies, and
that you add no other conditions whatsoever to those of this
License. You may not use technical measures to obstruct or
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<para>You may also lend copies, under the same conditions stated
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</sect1>
<sect1 id="gfdl-3">
<title>COPYING IN QUANTITY</title>
<para>If you publish printed copies of the Document numbering more
than 100, and the Document's license notice requires Cover Texts,
you must enclose the copies in covers that carry, clearly and
legibly, all these Cover Texts: Front-Cover Texts on the front
cover, and Back-Cover Texts on the back cover. Both covers must
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copies. The front cover must present the full title with all
words of the title equally prominent and visible. You may add
other material on the covers in addition. Copying with changes
limited to the covers, as long as they preserve the title of the
Document and satisfy these conditions, can be treated as verbatim
copying in other respects.</para>
<para>If the required texts for either cover are too voluminous to
fit legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto
adjacent pages.</para>
<para>If you publish or distribute Opaque copies of the Document
numbering more than 100, you must either include a
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state in or with each Opaque copy a publicly-accessible
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of the Document, free of added material, which the general
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charge using public-standard network protocols. If you use the
latter option, you must take reasonably prudent steps, when you
begin distribution of Opaque copies in quantity, to ensure that
this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you
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<para>It is requested, but not required, that you contact the
authors of the Document well before redistributing any large
number of copies, to give them a chance to provide you with an
updated version of the Document.</para>
</sect1>
<sect1 id="gfdl-4">
<title>MODIFICATIONS</title>
<para>You may copy and distribute a Modified Version of the
Document under the conditions of sections 2 and 3 above, provided
that you release the Modified Version under precisely this
License, with the Modified Version filling the role of the
Document, thus licensing distribution and modification of the
Modified Version to whoever possesses a copy of it. In addition,
you must do these things in the Modified Version:</para>
<orderedlist numeration="upperalpha">
<listitem><para>Use in the Title Page
(and on the covers, if any) a title distinct from that of the
Document, and from those of previous versions (which should, if
there were any, be listed in the History section of the
Document). You may use the same title as a previous version if
the original publisher of that version gives permission.</para>
</listitem>
<listitem><para>List on the Title Page,
as authors, one or more persons or entities responsible for
authorship of the modifications in the Modified Version,
together with at least five of the principal authors of the
Document (all of its principal authors, if it has less than
five).</para>
</listitem>
<listitem><para>State on the Title page
the name of the publisher of the Modified Version, as the
publisher.</para>
</listitem>
<listitem><para>Preserve all the
copyright notices of the Document.</para>
</listitem>
<listitem><para>Add an appropriate
copyright notice for your modifications adjacent to the other
copyright notices.</para>
</listitem>
<listitem><para>Include, immediately
after the copyright notices, a license notice giving the public
permission to use the Modified Version under the terms of this
License, in the form shown in the Addendum below.</para>
</listitem>
<listitem><para>Preserve in that license
notice the full lists of Invariant Sections and required Cover
Texts given in the Document's license notice.</para>
</listitem>
<listitem><para>Include an unaltered
copy of this License.</para>
</listitem>
<listitem><para>Preserve the section
entitled "History", and its title, and add to it an item stating
at least the title, year, new authors, and publisher of the
Modified Version as given on the Title Page. If there is no
section entitled "History" in the Document, create one stating
the title, year, authors, and publisher of the Document as given
on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.</para>
</listitem>
<listitem><para>Preserve the network
location, if any, given in the Document for public access to a
Transparent copy of the Document, and likewise the network
locations given in the Document for previous versions it was
based on. These may be placed in the "History" section. You
may 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.</para>
</listitem>
<listitem><para>In any section entitled
"Acknowledgements" or "Dedications", preserve the section's
title, and preserve in the section all the substance and tone of
each of the contributor acknowledgements and/or dedications
given therein.</para>
</listitem>
<listitem><para>Preserve all the
Invariant Sections of the Document, unaltered in their text and
in their titles. Section numbers or the equivalent are not
considered part of the section titles.</para>
</listitem>
<listitem><para>Delete any section
entitled "Endorsements". Such a section may not be included in
the Modified Version.</para>
</listitem>
<listitem><para>Do not retitle any
existing section as "Endorsements" or to conflict in title with
any Invariant Section.</para>
</listitem>
</orderedlist>
<para>If the Modified Version includes new front-matter sections
or appendices that qualify as Secondary Sections and contain no
material copied from the Document, you may at your option
designate some or all of these sections as invariant. To do this,
add their titles to the list of Invariant Sections in the Modified
Version's license notice. These titles must be distinct from any
other section titles.</para>
<para>You may add a section entitled "Endorsements", provided it
contains nothing but endorsements of your Modified Version by
various parties--for example, statements of peer review or that
the text has been approved by an organization as the authoritative
definition of a standard.</para>
<para>You may add a passage of up to five words as a Front-Cover
Text, and a passage of up to 25 words as a Back-Cover Text, to the
end of the list of Cover Texts in the Modified Version. Only one
passage of Front-Cover Text and one of Back-Cover Text may be
added by (or through arrangements made by) any one entity. If the
Document already includes a cover text for the same cover,
previously added by you or by arrangement made by the same entity
you are acting on behalf of, you may not add another; but you may
replace the old one, on explicit permission from the previous
publisher that added the old one.</para>
<para>The author(s) and publisher(s) of the Document do not by
this License give permission to use their names for publicity for
or to assert or imply endorsement of any Modified Version.</para>
</sect1>
<sect1 id="gfdl-5">
<title>COMBINING DOCUMENTS</title>
<para>You may combine the Document with other documents released
under this License, under the terms defined in section 4 above for
modified versions, provided that you include in the combination
all of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your
combined work in its license notice.</para>
<para>The combined work need only contain one copy of this
License, and multiple identical Invariant Sections may be replaced
with a single copy. If there are multiple Invariant Sections with
the same name but different contents, make the title of each such
section unique by adding at the end of it, in parentheses, the
name of the original author or publisher of that section if known,
or else a unique number. Make the same adjustment to the section
titles in the list of Invariant Sections in the license notice of
the combined work.</para>
<para>In the combination, you must combine any sections entitled
"History" in the various original documents, forming one section
entitled "History"; likewise combine any sections entitled
"Acknowledgements", and any sections entitled "Dedications". You
must delete all sections entitled "Endorsements."</para>
</sect1>
<sect1 id="gfdl-6">
<title>COLLECTIONS OF DOCUMENTS</title>
<para>You may make a collection consisting of the Document and
other documents released under this License, and replace the
individual copies of this License in the various documents with a
single copy that is included in the collection, provided that you
follow the rules of this License for verbatim copying of each of
the documents in all other respects.</para>
<para>You may extract a single document from such a collection,
and distribute it individually under this License, provided you
insert a copy of this License into the extracted document, and
follow this License in all other respects regarding verbatim
copying of that document.</para>
</sect1>
<sect1 id="gfdl-7">
<title>AGGREGATION WITH INDEPENDENT WORKS</title>
<para>A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of
a storage or distribution medium, does not as a whole count as a
Modified Version of the Document, provided no compilation
copyright is claimed for the compilation. Such a compilation is
called an "aggregate", and this License does not apply to the
other self-contained works thus compiled with the Document, on
account of their being thus compiled, if they are not themselves
derivative works of the Document.</para>
<para>If the Cover Text requirement of section 3 is applicable to
these copies of the Document, then if the Document is less than
one quarter of the entire aggregate, the Document's Cover Texts
may be placed on covers that surround only the Document within the
aggregate. Otherwise they must appear on covers around the whole
aggregate.</para>
</sect1>
<sect1 id="gfdl-8">
<title>TRANSLATION</title>
<para>Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires
special permission from their copyright holders, but you may
include translations of some or all Invariant Sections in addition
to the original versions of these Invariant Sections. You may
include a translation of this License provided that you also
include the original English version of this License. In case of
a disagreement between the translation and the original English
version of this License, the original English version will
prevail.</para>
</sect1>
<sect1 id="gfdl-9">
<title>TERMINATION</title>
<para>You may not copy, modify, sublicense, or distribute the
Document except as expressly provided for under this License. Any
other attempt to copy, modify, sublicense or distribute the
Document is void, and will automatically terminate your rights
under this License. However, parties who have received copies, or
rights, from you under this License will not have their licenses
terminated so long as such parties remain in full
compliance.</para>
</sect1>
<sect1 id="gfdl-10">
<title>FUTURE REVISIONS OF THIS LICENSE</title>
<para>The Free Software Foundation may publish new, revised
versions of the GNU Free Documentation License from time to time.
Such new versions will be similar in spirit to the present
version, but may differ in detail to address new problems or
concerns. See <ulink
url="http://www.gnu.org/copyleft/">http://www.gnu.org/copyleft/</ulink>.</para>
<para>Each version of the License is given a distinguishing
version number. If the Document specifies that a particular
numbered version of this License "or any later version" applies to
it, you have the option of following the terms and conditions
either of that specified version or of any later version that has
been published (not as a draft) by the Free Software Foundation.
If the Document does not specify a version number of this License,
you may choose any version ever published (not as a draft) by the
Free Software Foundation.</para>
</sect1>
<sect1 id="gfdl-11">
<title>How to use this License for your documents</title>
<para>To use this License in a document you have written, include
a copy of the License in the document and put the following
copyright and license notices just after the title page:</para>
<blockquote><para>
Copyright (c) YEAR YOUR NAME.
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 the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
A copy of the license is included in the section entitled "GNU
Free Documentation License".
</para></blockquote>
<para>If you have no Invariant Sections, write "with no Invariant
Sections" instead of saying which ones are invariant. If you have
no Front-Cover Texts, write "no Front-Cover Texts" instead of
"Front-Cover Texts being LIST"; likewise for Back-Cover
Texts.</para>
<para>If your document contains nontrivial examples of program
code, we recommend releasing these examples in parallel under your
choice of free software license, such as the GNU General Public
License, to permit their use in free software.</para>
</sect1>
</appendix>
</article>
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