docs/xml/writing-tools.xml

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<chapter id="writing-tools" xreflabel="Writing a New Valgrind Tool">
<title>Writing a New Valgrind Tool</title>

<sect1 id="writing-tools.intro" xreflabel="Introduction">
<title>Introduction</title>

<sect2 id="writing-tools.supexec" xreflabel="Supervised Execution">
<title>Supervised Execution</title>

<para>Valgrind provides a generic infrastructure for supervising
the execution of programs.  This is done by providing a way to
instrument programs in very precise ways, making it relatively
easy to support activities such as dynamic error detection and
profiling.</para>

<para>Although writing a tool is not easy, and requires learning
quite a few things about Valgrind, it is much easier than
instrumenting a program from scratch yourself.</para>

</sect2>


<sect2 id="writing-tools.tools" xreflabel="Tools">
<title>Tools</title>

<para>The key idea behind Valgrind's architecture is the division
between its "core" and "tools".</para>

<para>The core provides the common low-level infrastructure to
support program instrumentation, including the x86-to-x86 JIT
compiler, low-level memory manager, signal handling and a
scheduler (for pthreads).  It also provides certain services that
are useful to some but not all tools, such as support for error
recording and suppression.</para>

<para>But the core leaves certain operations undefined, which
must be filled by tools.  Most notably, tools define how program
code should be instrumented.  They can also define certain
variables to indicate to the core that they would like to use
certain services, or be notified when certain interesting events
occur.  But the core takes care of all the hard work.</para>

</sect2>


<sect2 id="writing-tools.execspaces" xreflabel="Execution Spaces">
<title>Execution Spaces</title>

<para>An important concept to understand before writing a tool is
that there are three spaces in which program code executes:</para>


<orderedlist>

 <listitem>
  <para>User space: this covers most of the program's execution.
  The tool is given the code and can instrument it any way it
  likes, providing (more or less) total control over the
  code.</para>

  <para>Code executed in user space includes all the program
  code, almost all of the C library (including things like the
  dynamic linker), and almost all parts of all other
  libraries.</para>
 </listitem>

  <listitem>
   <para>Core space: a small proportion of the program's execution
   takes place entirely within Valgrind's core.  This includes:</para>
   <itemizedlist>
    <listitem>
      <para>Dynamic memory management 
      (<computeroutput>malloc()</computeroutput> etc.)</para>
    </listitem>
    <listitem>
     <para>Pthread operations and scheduling</para>
    </listitem>
    <listitem>
     <para>Signal handling</para>
    </listitem>
   </itemizedlist>

   <para>A tool has no control over these operations; it never
   "sees" the code doing this work and thus cannot instrument it.
   However, the core provides hooks so a tool can be notified
   when certain interesting events happen, for example when when
   dynamic memory is allocated or freed, the stack pointer is
   changed, or a pthread mutex is locked, etc.</para>

   <para>Note that these hooks only notify tools of events
   relevant to user space.  For example, when the core allocates
   some memory for its own use, the tool is not notified of this,
   because it's not directly part of the supervised program's
   execution.</para>
  </listitem>

  <listitem>
   <para>Kernel space: execution in the kernel.  Two kinds:</para>
    <orderedlist>
     <listitem>
      <para>System calls: can't be directly observed by either
      the tool or the core.  But the core does have some idea of
      what happens to the arguments, and it provides hooks for a
      tool to wrap system calls.</para>
     </listitem>
     <listitem>
      <para>Other: all other kernel activity (e.g. process
      scheduling) is totally opaque and irrelevant to the
      program.</para>
     </listitem>
    </orderedlist>
  </listitem>

  <listitem>
   <para>It should be noted that a tool only has direct control
   over code executed in user space.  This is the vast majority
   of code executed, but it is not absolutely all of it, so any
   profiling information recorded by a tool won't be totally
   accurate.</para>
  </listitem>

</orderedlist>

</sect2>

</sect1>



<sect1 id="writing-tools.writingatool" xreflabel="Writing a Tool">
<title>Writing a Tool</title>


<sect2 id="writing-tools.whywriteatool" xreflabel="Why write a tool?">
<title>Why write a tool?</title>

<para>Before you write a tool, you should have some idea of what
it should do.  What is it you want to know about your programs of
interest?  Consider some existing tools:</para>

<itemizedlist>

 <listitem>
  <para><command>memcheck</command>: among other things, performs
  fine-grained validity and addressibility checks of every memory
  reference performed by the program.</para>
 </listitem>

 <listitem>
  <para><command>addrcheck</command>: performs lighterweight
  addressibility checks of every memory reference performed by
  the program.</para>
 </listitem>

 <listitem>
  <para><command>cachegrind</command>: tracks every instruction
  and memory reference to simulate instruction and data caches,
  tracking cache accesses and misses that occur on every line in
  the program.</para>
 </listitem>

 <listitem>
  <para><command>helgrind</command>: tracks every memory access
  and mutex lock/unlock to determine if a program contains any
  data races.</para>
 </listitem>

 <listitem>
  <para><command>lackey</command>: does simple counting of
  various things: the number of calls to a particular function
  (<computeroutput>_dl_runtime_resolve()</computeroutput>); the
  number of basic blocks, x86 instruction, UCode instructions
  executed; the number of branches executed and the proportion of
  those which were taken.</para>
 </listitem>
</itemizedlist>

<para>These examples give a reasonable idea of what kinds of
things Valgrind can be used for.  The instrumentation can range
from very lightweight (e.g. counting the number of times a
particular function is called) to very intrusive (e.g.
memcheck's memory checking).</para>

</sect2>


<sect2 id="writing-tools.suggestedtools" xreflabel="Suggested tools">
<title>Suggested tools</title>

<para>Here is a list of ideas we have had for tools that should
not be too hard to implement.</para>

<itemizedlist>
 <listitem>
  <para><command>branch profiler</command>: A machine's branch
  prediction hardware could be simulated, and each branch
  annotated with the number of predicted and mispredicted
  branches.  Would be implemented quite similarly to Cachegrind,
  and could reuse the
  <computeroutput>cg_annotate</computeroutput> script to annotate
  source code.</para>

  <para>The biggest difficulty with this is the simulation; the
  chip-makers are very cagey about how their chips do branch
  prediction.  But implementing one or more of the basic
  algorithms could still give good information.</para>
 </listitem>

 <listitem>
  <para><command>coverage tool</command>: Cachegrind can already
  be used for doing test coverage, but it's massive overkill to
  use it just for that.</para>

  <para>It would be easy to write a coverage tool that records
  how many times each basic block was recorded.  Again, the
  <computeroutput>cg_annotate</computeroutput> script could be
  used for annotating source code with the gathered information.
  Although, <computeroutput>cg_annotate</computeroutput> is only
  designed for working with single program runs.  It could be
  extended relatively easily to deal with multiple runs of a
  program, so that the coverage of a whole test suite could be
  determined.</para>

  <para>In addition to the standard coverage information, such a
  tool could record extra information that would help a user
  generate test cases to exercise unexercised paths.  For
  example, for each conditional branch, the tool could record all
  inputs to the conditional test, and print these out when
  annotating.</para>
 </listitem>

 <listitem>
  <para><command>run-time type checking</command>: A nice example
  of a dynamic checker is given in this paper:</para>
  <address>Debugging via Run-Time Type Checking
  Alexey Loginov, Suan Hsi Yong, Susan Horwitz and Thomas Reps
  Proceedings of Fundamental Approaches to Software Engineering
  April 2001.
  </address>

  <para>Similar is the tool described in this paper:</para>
  <address>Run-Time Type Checking for Binary Programs
  Michael Burrows, Stephen N. Freund, Janet L. Wiener
  Proceedings of the 12th International Conference on Compiler Construction (CC 2003)
  April 2003.
  </address>

  <para>This approach can find quite a range of bugs,
  particularly in C and C++ programs, and could be implemented
  quite nicely as a Valgrind tool.</para>

  <para>Ways to speed up this run-time type checking are
  described in this paper:</para>
  <address>Reducing the Overhead of Dynamic Analysis
  Suan Hsi Yong and Susan Horwitz
  Proceedings of Runtime Verification '02
  July 2002.
  </address>

  <para>Valgrind's client requests could be used to pass
  information to a tool about which elements need instrumentation
  and which don't.</para>
 </listitem>
</itemizedlist>

<para>We would love to hear from anyone who implements these or
other tools.</para>

</sect2>


<sect2 id="writing-tools.howtoolswork" xreflabel="How tools work">
<title>How tools work</title>

<para>Tools must define various functions for instrumenting
programs that are called by Valgrind's core, yet they must be
implemented in such a way that they can be written and compiled
without touching Valgrind's core.  This is important, because one
of our aims is to allow people to write and distribute their own
tools that can be plugged into Valgrind's core easily.</para>

<para>This is achieved by packaging each tool into a separate
shared object which is then loaded ahead of the core shared
object <computeroutput>valgrind.so</computeroutput>, using the
dynamic linker's <computeroutput>LD_PRELOAD</computeroutput>
variable.  Any functions defined in the tool that share the name
with a function defined in core (such as the instrumentation
function <computeroutput>TL_(instrument)()</computeroutput>)
override the core's definition.  Thus the core can call the
necessary tool functions.</para>

<para>This magic is all done for you; the shared object used is
chosen with the <computeroutput>--tool</computeroutput> option to
the <computeroutput>valgrind</computeroutput> startup script.
The default tool used is
<computeroutput>memcheck</computeroutput>, Valgrind's original
memory checker.</para>

</sect2>


<sect2 id="writing-tools.gettingcode" xreflabel="Getting the code">
<title>Getting the code</title>

<para>To write your own tool, you'll need to check out a copy of
Valgrind from the CVS repository, rather than using a packaged
distribution.  This is because it contains several extra files
needed for writing tools.</para>

<para>To check out the code from the CVS repository, first login:</para>
<programlisting><![CDATA[
cvs -d:pserver:anonymous@cvs.valgrind.sourceforge.net:/cvsroot/valgrind
login]]></programlisting>

<para>Then checkout the code.  To get a copy of the current
development version (recommended for the brave only):</para>
<programlisting><![CDATA[
cvs -z3 -d:pserver:anonymous@cvs.valgrind.sourceforge.net:/cvsroot/valgrind 
co valgrind]]></programlisting>

<para>To get a copy of the stable released branch:</para>
<programlisting><![CDATA[
cvs -z3 -d:pserver:anonymous@cvs.valgrind.sourceforge.net:/cvsroot/valgrind
co -r <TAG> valgrind]]></programlisting>

<para>where &lt;<computeroutput>TAG</computeroutput>&gt; has the
form <computeroutput>VALGRIND_X_Y_Z</computeroutput> for version
X.Y.Z.</para>

</sect2>


<sect2 id="writing-tools.gettingstarted" xreflabel="Getting started">
<title>Getting started</title>

<para>Valgrind uses GNU <computeroutput>automake</computeroutput>
and <computeroutput>autoconf</computeroutput> for the creation of
Makefiles and configuration.  But don't worry, these instructions
should be enough to get you started even if you know nothing
about those tools.</para>

<para>In what follows, all filenames are relative to Valgrind's
top-level directory <computeroutput>valgrind/</computeroutput>.</para>

<orderedlist>
 <listitem>
  <para>Choose a name for the tool, and an abbreviation that can
  be used as a short prefix.  We'll use
  <computeroutput>foobar</computeroutput> and
  <computeroutput>fb</computeroutput> as an example.</para>
 </listitem>

 <listitem>
  <para>Make a new directory
  <computeroutput>foobar/</computeroutput> which will hold the
  tool.</para>
 </listitem>

 <listitem>
  <para>Copy <computeroutput>none/Makefile.am</computeroutput>
  into <computeroutput>foobar/</computeroutput>.  Edit it by
  replacing all occurrences of the string
  <computeroutput>"none"</computeroutput> with
  <computeroutput>"foobar"</computeroutput> and the one
  occurrence of the string <computeroutput>"nl_"</computeroutput>
  with <computeroutput>"fb_"</computeroutput>.  It might be worth
  trying to understand this file, at least a little; you might
  have to do more complicated things with it later on.  In
  particular, the name of the
  <computeroutput>vgtool_foobar_so_SOURCES</computeroutput>
  variable determines the name of the tool's shared object, which
  determines what name must be passed to the
  <computeroutput>--tool</computeroutput> option to use the
  tool.</para>
 </listitem>

 <listitem>
  <para>Copy <filename>none/nl_main.c</filename> into
  <computeroutput>foobar/</computeroutput>, renaming it as
  <filename>fb_main.c</filename>.  Edit it by changing the lines
  in <computeroutput>TL_(pre_clo_init)()</computeroutput> to
  something appropriate for the tool.  These fields are used in
  the startup message, except for
  <computeroutput>bug_reports_to</computeroutput> which is used
  if a tool assertion fails.</para>
 </listitem>

  <listitem>
   <para>Edit <computeroutput>Makefile.am</computeroutput>,
   adding the new directory
   <computeroutput>foobar</computeroutput> to the
   <computeroutput>SUBDIRS</computeroutput> variable.</para>
  </listitem>

  <listitem>
   <para>Edit <computeroutput>configure.in</computeroutput>,
   adding <computeroutput>foobar/Makefile</computeroutput> to the
   <computeroutput>AC_OUTPUT</computeroutput> list.</para>
  </listitem>

  <listitem>
   <para>Run:</para>
<programlisting><![CDATA[
  autogen.sh
  ./configure --prefix=`pwd`/inst
  make install]]></programlisting>

   <para>It should automake, configure and compile without
   errors, putting copies of the tool's shared object
   <computeroutput>vgtool_foobar.so</computeroutput> in
   <computeroutput>foobar/</computeroutput> and
   <computeroutput>inst/lib/valgrind/</computeroutput>.</para>
  </listitem>

  <listitem>
   <para>You can test it with a command like:</para>
<programlisting><![CDATA[
  inst/bin/valgrind --tool=foobar date]]></programlisting>

   <para>(almost any program should work;
   <computeroutput>date</computeroutput> is just an example).
   The output should be something like this:</para>
<programlisting><![CDATA[
  ==738== foobar-0.0.1, a foobarring tool for x86-linux.
  ==738== Copyright (C) 1066AD, and GNU GPL'd, by J. Random Hacker.
  ==738== Built with valgrind-1.1.0, a program execution monitor.
  ==738== Copyright (C) 2000-2003, and GNU GPL'd, by Julian Seward.
  ==738== Estimated CPU clock rate is 1400 MHz
  ==738== For more details, rerun with: -v
  ==738== Wed Sep 25 10:31:54 BST 2002
  ==738==]]></programlisting>

   <para>The tool does nothing except run the program
   uninstrumented.</para>
  </listitem>

</orderedlist>

<para>These steps don't have to be followed exactly - you can
choose different names for your source files, and use a different
<computeroutput>--prefix</computeroutput> for
<computeroutput>./configure</computeroutput>.</para>

<para>Now that we've setup, built and tested the simplest
possible tool, onto the interesting stuff...</para>

</sect2>



<sect2 id="writing-tools.writingcode" xreflabel="Writing the Code">
<title>Writing the code</title>

<para>A tool must define at least these four functions:</para>
<programlisting><![CDATA[
  TL_(pre_clo_init)()
  TL_(post_clo_init)()
  TL_(instrument)()
  TL_(fini)()]]></programlisting>

<para>Also, it must use the macro
<computeroutput>VG_DETERMINE_INTERFACE_VERSION</computeroutput>
exactly once in its source code.  If it doesn't, you will get a
link error involving
<computeroutput>VG_(tool_interface_major_version)</computeroutput>.
This macro is used to ensure the core/tool interface used by the
core and a plugged-in tool are binary compatible.</para>

<para>In addition, if a tool wants to use some of the optional
services provided by the core, it may have to define other
functions.</para>

</sect2>



<sect2 id="writing-tools.init" xreflabel="Initialisation">
<title>Initialisation</title>

<para>Most of the initialisation should be done in
<computeroutput>TL_(pre_clo_init)()</computeroutput>.  Only use
<computeroutput>TL_(post_clo_init)()</computeroutput> if a tool
provides command line options and must do some initialisation
after option processing takes place
(<computeroutput>"clo"</computeroutput> stands for "command line
options").</para>

<para>First of all, various "details" need to be set for a tool,
using the functions
<computeroutput>VG_(details_*)()</computeroutput>.  Some are all
compulsory, some aren't.  Some are used when constructing the
startup message,
<computeroutput>detail_bug_reports_to</computeroutput> is used if
<computeroutput>VG_(tool_panic)()</computeroutput> is ever
called, or a tool assertion fails.  Others have other uses.</para>

<para>Second, various "needs" can be set for a tool, using the
functions <computeroutput>VG_(needs_*)()</computeroutput>.  They
are mostly booleans, and can be left untouched (they default to
<computeroutput>False</computeroutput>).  They determine whether
a tool can do various things such as: record, report and suppress
errors; process command line options; wrap system calls; record
extra information about malloc'd blocks, etc.</para>

<para>For example, if a tool wants the core's help in recording
and reporting errors, it must set the
<computeroutput>tool_errors</computeroutput> need to
<computeroutput>True</computeroutput>, and then provide
definitions of six functions for comparing errors, printing out
errors, reading suppressions from a suppressions file, etc.
While writing these functions requires some work, it's much less
than doing error handling from scratch because the core is doing
most of the work.  See the type
<computeroutput>VgNeeds</computeroutput> in
<filename>include/tool.h</filename> for full details of all
the needs.</para>

<para>Third, the tool can indicate which events in core it wants
to be notified about, using the functions
<computeroutput>VG_(track_*)()</computeroutput>.  These include
things such as blocks of memory being malloc'd, the stack pointer
changing, a mutex being locked, etc.  If a tool wants to know
about this, it should set the relevant pointer in the structure
to point to a function, which will be called when that event
happens.</para>

<para>For example, if the tool want to be notified when a new
block of memory is malloc'd, it should call
<computeroutput>VG_(track_new_mem_heap)()</computeroutput> with
an appropriate function pointer, and the assigned function will
be called each time this happens.</para>

<para>More information about "details", "needs" and "trackable
events" can be found in
<filename>include/tool.h</filename>.</para>

</sect2>



<sect2 id="writing-tools.instr" xreflabel="Instrumentation">
<title>Instrumentation</title>

<para><computeroutput>TL_(instrument)()</computeroutput> is the
interesting one.  It allows you to instrument
<emphasis>UCode</emphasis>, which is Valgrind's RISC-like
intermediate language.  UCode is described in 
<xref linkend="mc-tech-docs.ucode"/>.</para>

<para>The easiest way to instrument UCode is to insert calls to C
functions when interesting things happen.  See the tool "Lackey"
(<filename>lackey/lk_main.c</filename>) for a simple example of
this, or Cachegrind (<filename>cachegrind/cg_main.c</filename>)
for a more complex example.</para>

<para>A much more complicated way to instrument UCode, albeit one
that might result in faster instrumented programs, is to extend
UCode with new UCode instructions.  This is recommended for
advanced Valgrind hackers only!  See Memcheck for an example.</para>

</sect2>



<sect2 id="writing-tools.fini" xreflabel="Finalisation">
<title>Finalisation</title>

<para>This is where you can present the final results, such as a
summary of the information collected.  Any log files should be
written out at this point.</para>

</sect2>



<sect2 id="writing-tools.otherinfo" xreflabel="Other Important Information">
<title>Other Important Information</title>

<para>Please note that the core/tool split infrastructure is
quite complex and not brilliantly documented.  Here are some
important points, but there are undoubtedly many others that I
should note but haven't thought of.</para>

<para>The file <filename>include/tool.h</filename> contains
all the types, macros, functions, etc. that a tool should
(hopefully) need, and is the only <filename>.h</filename> file a
tool should need to
<computeroutput>#include</computeroutput>.</para>

<para>In particular, you probably shouldn't use anything from the
C library (there are deep reasons for this, trust us).  Valgrind
provides an implementation of a reasonable subset of the C
library, details of which are in
<filename>tool.h</filename>.</para>

<para>Similarly, when writing a tool, you shouldn't need to look
at any of the code in Valgrind's core.  Although it might be
useful sometimes to help understand something.</para>

<para><filename>tool.h</filename> has a reasonable amount of
documentation in it that should hopefully be enough to get you
going.  But ultimately, the tools distributed (Memcheck,
Addrcheck, Cachegrind, Lackey, etc.) are probably the best
documentation of all, for the moment.</para>

<para>Note that the <computeroutput>VG_</computeroutput> and
<computeroutput>TL_</computeroutput> macros are used heavily.
These just prepend longer strings in front of names to avoid
potential namespace clashes.  We strongly recommend using the
<computeroutput>TL_</computeroutput> macro for any global
functions and variables in your tool, or writing a similar
macro.</para>

</sect2>


<sect2 id="writing-tools.advice" xreflabel="Words of Advice">
<title>Words of Advice</title>

<para>Writing and debugging tools is not trivial.  Here are some
suggestions for solving common problems.</para>


<sect3 id="writing-tools.segfaults">
<title>Segmentation Faults</title>

<para>If you are getting segmentation faults in C functions used
by your tool, the usual GDB command:</para>
<screen><![CDATA[
  gdb <prog> core]]></screen>
<para>usually gives the location of the segmentation fault.</para>

</sect3>


<sect3 id="writing-tools.debugfns">
<title>Debugging C functions</title>

<para>If you want to debug C functions used by your tool, you can
attach GDB to Valgrind with some effort:</para>
<orderedlist>
 <listitem>
  <para>Enable the following code in
  <filename>coregrind/vg_main.c</filename> by changing
  <computeroutput>if (0)</computeroutput> 
  into <computeroutput>if (1)</computeroutput>:
<programlisting><![CDATA[
  /* Hook to delay things long enough so we can get the pid and
     attach GDB in another shell. */
  if (0) { 
    Int p, q;
    for ( p = 0; p < 50000; p++ )
      for ( q = 0; q < 50000; q++ ) ;
  }]]></programlisting>
  and rebuild Valgrind.</para>
 </listitem>

 <listitem>
  <para>Then run:</para>
<programlisting><![CDATA[
  valgrind <prog>]]></programlisting>
  <para>Valgrind starts the program, printing its process id, and
  then delays for a few seconds (you may have to change the loop
  bounds to get a suitable delay).</para>
 </listitem>

 <listitem>
  <para>In a second shell run:</para>
<programlisting><![CDATA[
  gdb <prog pid>]]></programlisting>
 </listitem>

</orderedlist>

<para>GDB may be able to give you useful information.  Note that
by default most of the system is built with
<computeroutput>-fomit-frame-pointer</computeroutput>, and you'll
need to get rid of this to extract useful tracebacks from GDB.</para>

</sect3>


<sect3 id="writing-tools.ucode-probs">
<title>UCode Instrumentation Problems</title>

<para>If you are having problems with your UCode instrumentation,
it's likely that GDB won't be able to help at all.  In this case,
Valgrind's <computeroutput>--trace-codegen</computeroutput>
option is invaluable for observing the results of
instrumentation.</para>

</sect3>


<sect3 id="writing-tools.misc">
<title>Miscellaneous</title>

<para>If you just want to know whether a program point has been
reached, using the <computeroutput>OINK</computeroutput> macro
(in <filename>include/tool.h</filename>) can be easier than
using GDB.</para>

<para>The other debugging command line options can be useful too
(run <computeroutput>valgrind -h</computeroutput> for the
list).</para>

</sect3>

</sect2>

</sect1>



<sect1 id="writing-tools.advtopics" xreflabel="Advanced Topics">
<title>Advanced Topics</title>

<para>Once a tool becomes more complicated, there are some extra
things you may want/need to do.</para>

<sect2 id="writing-tools.suppressions" xreflabel="Suppressions">
<title>Suppressions</title>

<para>If your tool reports errors and you want to suppress some
common ones, you can add suppressions to the suppression files.
The relevant files are
<computeroutput>valgrind/*.supp</computeroutput>; the final
suppression file is aggregated from these files by combining the
relevant <computeroutput>.supp</computeroutput> files depending
on the versions of linux, X and glibc on a system.</para>

<para>Suppression types have the form
<computeroutput>tool_name:suppression_name</computeroutput>.  The
<computeroutput>tool_name</computeroutput> here is the name you
specify for the tool during initialisation with
<computeroutput>VG_(details_name)()</computeroutput>.</para>

</sect2>


<!--
<sect2 id="writing-tools.docs" xreflabel="Documentation">
<title>Documentation</title>

<para>As of version &rel-version;, Valgrind documentation has
been converted to XML. Why? 
See <ulink url="http://www.ucc.ie/xml/">The XML FAQ</ulink>.
</para>


<sect3 id="writing-tools.xml" xreflabel="The XML Toolchain">
<title>The XML Toolchain</title>

<para>If you are feeling conscientious and want to write some
documentation for your tool, please use XML.  The Valgrind
Docs use the following toolchain and versions:</para>

<programlisting>
 xmllint:   using libxml version 20607
 xsltproc:  using libxml 20607, libxslt 10102 and libexslt 802
 pdfxmltex: pdfTeX (Web2C 7.4.5) 3.14159-1.10b
 pdftops:   version 3.00
 DocBook:   version 4.2
</programlisting>

<para><command>Latency:</command> you should note that latency is
a big problem: DocBook is constantly being updated, but the tools
tend to lag behind somewhat.  It is important that the versions
get on with each other, so if you decide to upgrade something,
then you need to ascertain whether things still work nicely -
this *cannot* be assumed.</para>

<para><command>Stylesheets:</command> The Valgrind docs use
various custom stylesheet layers, all of which are in
<computeroutput>valgrind/docs/lib/</computeroutput>. You
shouldn't need to modify these in any way.</para>

<para><command>Catalogs:</command> Assuming that you have the
various tools listed above installed, you will probably need to
modify
<computeroutput>valgrind/docs/lib/vg-catalog.xml</computeroutput>
so that the parser can find your DocBook installation. Catalogs
provide a mapping from generic addresses to specific local
directories on a given machine.  Just add another
<computeroutput>group</computeroutput> to this file, reflecting
your local installation.</para>

</sect3>


<sect3 id="writing-tools.writing" xreflabel="Writing the Documentation">
<title>Writing the Documentation</title>

<para>If you aren't confident using XML, or you have problems
with the toolchain, then write your documentation in text format,
email it to
<computeroutput>valgrind@valgrind.org</computeroutput>, and
someone will convert it to XML for you.  Otherwise, follow these
steps (using <computeroutput>foobar</computeroutput> as the
example tool name again):</para>

<orderedlist>

  <listitem>
   <para>Make a directory
  <computeroutput>valgrind/foobar/docs/</computeroutput>.</para>
 </listitem>

 <listitem>
  <para>Copy the xml tool documentation template file 
  <computeroutput>valgrind/docs/xml/tool-template.xml</computeroutput>
  to <computeroutput>foobar/docs/</computeroutput>, and rename it
  to
  <computeroutput>foobar/docs/fb-manual.xml</computeroutput>.</para>
  <para><command>Note</command>: there is a *really stupid* tetex
  bug with underscores in filenames, so don't use '_'.</para>
 </listitem>

 <listitem>
  <para>Write the documentation. There are some helpful bits and
  pieces on using xml markup in
  <filename>valgrind/docs/xml/xml_help.txt</filename>.</para>
 </listitem>

 <listitem>
  <para>Validate <computeroutput>foobar/docs/fb-manual.xml</computeroutput>
  using the shell script
  <filename>valgrind/docs/lib/xmlproc.sh</filename>.</para>
<screen><![CDATA[
% cd valgrind/docs/lib/
% ./xmlproc.sh -valid ../../foobar/docs/fb-manual.xml
]]></screen>

   <para>If you have linked to other documents in the Valgrind
   Documentation Set, you will get errors of the form:</para>

<screen><![CDATA[
fb-manual.xml:1632: element xref: validity error : 
        IDREF attribute linkend references an unknown ID "mc-tech-docs"
]]></screen>

   <para>Ignore (only) these - they will disappear when
   <filename>fb-manual.xml</filename> is integrated into the
   Set.</para>

  <para>Because the xml toolchain is fragile, it is important to
  ensure that <computeroutput>fb-manual.xml</computeroutput> won't
  break the documentation set build.  Note that just because an
  xml file happily transforms to html does not necessarily mean
  the same holds true for pdf/ps.</para>
 </listitem>

 <listitem>
  <para>You can (re-)generate <filename>fb-manual.html</filename>
  while you are writing <filename>fb-manual.xml</filename> to help
  you see how it's looking.  The generated file
  <filename>fb-manual.html</filename> will be output in
  <computeroutput>foobar/docs/</computeroutput>.</para>

<screen><![CDATA[
% ./xmlproc.sh -html ../../foobar/docs/fb-manual.xml
]]></screen>
 </listitem>

 <listitem>
  <para>When you have finished, generate html, pdf and ps output
  to check all is well:</para>

<screen><![CDATA[
% cp ../../foobar/fb-manual.xml .
% ./xmlproc.sh -test fb-manual.xml
]]></screen>

   <para>Check the output files (<filename>index.html,
   fb-manual.pdf, fb-manual.ps</filename>) in
   <computeroutput>/lib/test/</computeroutput> with the relevant
   viewers.  When you are happy and have finished tinkering with
   <computeroutput>fb-manual.xml</computeroutput>:</para>

<screen><![CDATA[
% ./xmlproc.sh -clean fb-manual.xml
]]></screen>
</listitem>

 <listitem>
  <para>In order for your documentation to be included in the
  User Manual, the relevant entries must be made in
  <filename>/valgrind/docs/xml/vg-bookset.xml</filename> in this
  format (hopefully, it should be pretty obvious):</para>

<programlisting><![CDATA[
<!ENTITY fb-manual   SYSTEM "../../foobar/docs/fb-manual.xml">
... ...
&fb-manual;
]]></programlisting>

  <para>Send a patch for this to
  <computeroutput>valgrind@valgrind.org</computeroutput>.</para>

  <para>To achieve true anality, try for a full doc-set build:</para>
<screen><![CDATA[
% cd valgrind/docs/
% make all
]]></screen>
 </listitem>

</orderedlist>

</sect3>

</sect2>
-->
<sect2 id="writing-tools.docs" xreflabel="Documentation">
<title>Documentation</title>

<para>As of version &rel-version;, Valgrind documentation has
been converted to XML. Why? 
See <ulink url="http://www.ucc.ie/xml/">The XML FAQ</ulink>.
</para>


<sect3 id="writing-tools.xml" xreflabel="The XML Toolchain">
<title>The XML Toolchain</title>

<para>If you are feeling conscientious and want to write some
documentation for your tool, please use XML.  The Valgrind
Docs use the following toolchain and versions:</para>

<programlisting>
 xmllint:   using libxml version 20607
 xsltproc:  using libxml 20607, libxslt 10102 and libexslt 802
 pdfxmltex: pdfTeX (Web2C 7.4.5) 3.14159-1.10b
 pdftops:   version 3.00
 DocBook:   version 4.2
</programlisting>

<para><command>Latency:</command> you should note that latency is
a big problem: DocBook is constantly being updated, but the tools
tend to lag behind somewhat.  It is important that the versions
get on with each other, so if you decide to upgrade something,
then you need to ascertain whether things still work nicely -
this *cannot* be assumed.</para>

<para><command>Stylesheets:</command> The Valgrind docs use
various custom stylesheet layers, all of which are in
<computeroutput>valgrind/docs/lib/</computeroutput>. You
shouldn't need to modify these in any way.</para>

<para><command>Catalogs:</command> Assuming that you have the
various tools listed above installed, you will probably need to
modify
<computeroutput>valgrind/docs/lib/vg-catalog.xml</computeroutput>
so that the parser can find your DocBook installation. Catalogs
provide a mapping from generic addresses to specific local
directories on a given machine.  Just add another
<computeroutput>group</computeroutput> to this file, reflecting
your local installation.</para>

</sect3>


<sect3 id="writing-tools.writing" xreflabel="Writing the Documentation">
<title>Writing the Documentation</title>

<para>Follow these steps (using <computeroutput>foobar</computeroutput>
as the example tool name again):</para>

<orderedlist>

  <listitem>
   <para>Make a directory
  <computeroutput>valgrind/foobar/docs/</computeroutput>.</para>
 </listitem>

 <listitem>
  <para>Copy the XML documentation file for the tool Nulgrind from
  <computeroutput>valgrind/none/docs/nl-manual.xml</computeroutput>
  to <computeroutput>foobar/docs/</computeroutput>, and rename it
  to
  <computeroutput>foobar/docs/fb-manual.xml</computeroutput>.</para>
  <para><command>Note</command>: there is a *really stupid* tetex
  bug with underscores in filenames, so don't use '_'.</para>
 </listitem>

 <listitem>
  <para>Write the documentation. There are some helpful bits and
  pieces on using xml markup in
  <filename>valgrind/docs/xml/xml_help.txt</filename>.</para>
 </listitem>

 <listitem>
  <para>Include it in the User Manual by adding the relevant entry must
  be added to <filename>valgrind/docs/xml/manual.xml</filename>.  Copy
  and edit an existing entry.</para>
 </listitem>

 <listitem>
  <para>Validate <computeroutput>foobar/docs/fb-manual.xml</computeroutput>
  using the following command from within <filename>valgrind/docs/</filename>:
  </para>
<screen><![CDATA[
% make valid
]]></screen>

   <para>You will probably get errors that look like this:</para>

<screen><![CDATA[
./xml/index.xml:5: element chapter: validity error : No declaration for
attribute base of element chapter
]]></screen>

  <para>Ignore (only) these -- they're not important.</para>

  <para>Because the xml toolchain is fragile, it is important to
  ensure that <filename>fb-manual.xml</filename> won't
  break the documentation set build.  Note that just because an
  xml file happily transforms to html does not necessarily mean
  the same holds true for pdf/ps.</para>
 </listitem>

 <listitem>
  <para>You can (re-)generate the HTML docs
  while you are writing <filename>fb-manual.xml</filename> to help
  you see how it's looking.  The generated files end up in
  <filename>valgrind/docs/html/</filename>.  Use the following
  command, within <filename>valgrind/docs/</filename>:</para>

<screen><![CDATA[
% make html-docs
]]></screen>
 </listitem>

 <listitem>
  <para>When you have finished, also generate pdf and ps output
  to check all is well, from within <filename>valgrind/docs/</filename>:
  </para>

<screen><![CDATA[
% make print-docs
]]></screen>

   <para>Check the output <filename>.pdf</filename> and
   <filename>.ps</filename> files in
   <computeroutput>valgrind/docs/print/</computeroutput>. 
   </para>
</listitem>

</orderedlist>

</sect3>

</sect2>


<sect2 id="writing-tools.regtests" xreflabel="Regression Tests">
<title>Regression Tests</title>

<para>Valgrind has some support for regression tests.  If you
want to write regression tests for your tool:</para>

<orderedlist>
 <listitem>
  <para>Make a directory
  <computeroutput>foobar/tests/</computeroutput>.</para>
 </listitem>

 <listitem>
  <para>Edit <computeroutput>foobar/Makefile.am</computeroutput>,
  adding <computeroutput>tests</computeroutput> to the
  <computeroutput>SUBDIRS</computeroutput> variable.</para>
 </listitem>

 <listitem>
  <para>Edit <computeroutput>configure.in</computeroutput>,
  adding <computeroutput>foobar/tests/Makefile</computeroutput>
  to the <computeroutput>AC_OUTPUT</computeroutput> list.</para>
 </listitem>

 <listitem>
  <para>Write
  <computeroutput>foobar/tests/Makefile.am</computeroutput>.  Use
  <computeroutput>memcheck/tests/Makefile.am</computeroutput> as
  an example.</para>
 </listitem>

 <listitem>
  <para>Write the tests, <computeroutput>.vgtest</computeroutput>
  test description files,
  <computeroutput>.stdout.exp</computeroutput> and
  <computeroutput>.stderr.exp</computeroutput> expected output
  files.  (Note that Valgrind's output goes to stderr.)  Some
  details on writing and running tests are given in the comments
  at the top of the testing script
  <computeroutput>tests/vg_regtest</computeroutput>.</para>
 </listitem>

 <listitem>
  <para>Write a filter for stderr results
  <computeroutput>foobar/tests/filter_stderr</computeroutput>.
  It can call the existing filters in
  <computeroutput>tests/</computeroutput>.  See
  <computeroutput>memcheck/tests/filter_stderr</computeroutput>
  for an example; in particular note the
  <computeroutput>$dir</computeroutput> trick that ensures the
  filter works correctly from any directory.</para>
 </listitem>

</orderedlist>

</sect2>



<sect2 id="writing-tools.profiling" xreflabel="Profiling">
<title>Profiling</title>

<para>To do simple tick-based profiling of a tool, include the
line:</para>
<programlisting><![CDATA[
  #include "vg_profile.c"]]></programlisting>
<para>in the tool somewhere, and rebuild (you may have to
<computeroutput>make clean</computeroutput> first).  Then run
Valgrind with the <computeroutput>--profile=yes</computeroutput>
option.</para>

<para>The profiler is stack-based; you can register a profiling
event with
<computeroutput>VGP_(register_profile_event)()</computeroutput>
and then use the <computeroutput>VGP_PUSHCC</computeroutput> and
<computeroutput>VGP_POPCC</computeroutput> macros to record time
spent doing certain things.  New profiling event numbers must not
overlap with the core profiling event numbers.  See
<filename>include/tool.h</filename> for details and Memcheck
for an example.</para>

</sect2>



<sect2 id="writing-tools.mkhackery" xreflabel="Other Makefile Hackery">
<title>Other Makefile Hackery</title>

<para>If you add any directories under
<computeroutput>valgrind/foobar/</computeroutput>, you will need
to add an appropriate <filename>Makefile.am</filename> to it, and
add a corresponding entry to the
<computeroutput>AC_OUTPUT</computeroutput> list in
<filename>valgrind/configure.in</filename>.</para>

<para>If you add any scripts to your tool (see Cachegrind for an
example) you need to add them to the
<computeroutput>bin_SCRIPTS</computeroutput> variable in
<filename>valgrind/foobar/Makefile.am</filename>.</para>

</sect2>



<sect2 id="writing-tools.ifacever" xreflabel="Core/tool Interface Versions">
<title>Core/tool Interface Versions</title>

<para>In order to allow for the core/tool interface to evolve
over time, Valgrind uses a basic interface versioning system.
All a tool has to do is use the
<computeroutput>VG_DETERMINE_INTERFACE_VERSION</computeroutput>
macro exactly once in its code.  If not, a link error will occur
when the tool is built.</para>

<para>The interface version number has the form X.Y.  Changes in
Y indicate binary compatible changes.  Changes in X indicate
binary incompatible changes.  If the core and tool has the same
major version number X they should work together.  If X doesn't
match, Valgrind will abort execution with an explanation of the
problem.</para>

<para>This approach was chosen so that if the interface changes
in the future, old tools won't work and the reason will be
clearly explained, instead of possibly crashing mysteriously.  We
have attempted to minimise the potential for binary incompatible
changes by means such as minimising the use of naked structs in
the interface.</para>

</sect2>

</sect1>



<sect1 id="writing-tools.finalwords" xreflabel="Final Words">
<title>Final Words</title>

<para>This whole core/tool business is under active development,
although it's slowly maturing.</para>

<para>The first consequence of this is that the core/tool
interface will continue to change in the future; we have no
intention of freezing it and then regretting the inevitable
stupidities.  Hopefully most of the future changes will be to add
new features, hooks, functions, etc, rather than to change old
ones, which should cause a minimum of trouble for existing tools,
and we've put some effort into future-proofing the interface to
avoid binary incompatibility.  But we can't guarantee anything.
The versioning system should catch any incompatibilities.  Just
something to be aware of.</para>

<para>The second consequence of this is that we'd love to hear
your feedback about it:</para>

<itemizedlist>
 <listitem>
  <para>If you love it or hate it</para>
 </listitem>
 <listitem>
  <para>If you find bugs</para>
 </listitem>
 <listitem>
  <para>If you write a tool</para>
 </listitem>
 <listitem>
  <para>If you have suggestions for new features, needs,
  trackable events, functions</para>
 </listitem>
 <listitem>
  <para>If you have suggestions for making tools easier to
  write</para>
 </listitem>
 <listitem>
  <para>If you have suggestions for improving this
  documentation</para>
 </listitem>
 <listitem>
  <para>If you don't understand something</para>
 </listitem>
</itemizedlist>

<para>or anything else!</para>

<para>Happy programming.</para>

</sect1>

</chapter>