You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
137 lines
6.9 KiB
HTML
137 lines
6.9 KiB
HTML
<html lang="en">
|
|
<head>
|
|
<title>Compiling - GNU gprof</title>
|
|
<meta http-equiv="Content-Type" content="text/html">
|
|
<meta name="description" content="GNU gprof">
|
|
<meta name="generator" content="makeinfo 4.13">
|
|
<link title="Top" rel="start" href="index.html#Top">
|
|
<link rel="prev" href="Introduction.html#Introduction" title="Introduction">
|
|
<link rel="next" href="Executing.html#Executing" title="Executing">
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
|
<!--
|
|
This file documents the gprof profiler of the GNU system.
|
|
|
|
Copyright (C) 1988-2015 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3
|
|
or any later version published by the Free Software Foundation;
|
|
with no Invariant Sections, with no Front-Cover Texts, and with no
|
|
Back-Cover Texts. A copy of the license is included in the
|
|
section entitled ``GNU Free Documentation License''.
|
|
|
|
-->
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
|
<style type="text/css"><!--
|
|
pre.display { font-family:inherit }
|
|
pre.format { font-family:inherit }
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
|
pre.smallexample { font-size:smaller }
|
|
pre.smalllisp { font-size:smaller }
|
|
span.sc { font-variant:small-caps }
|
|
span.roman { font-family:serif; font-weight:normal; }
|
|
span.sansserif { font-family:sans-serif; font-weight:normal; }
|
|
--></style>
|
|
</head>
|
|
<body>
|
|
<div class="node">
|
|
<a name="Compiling"></a>
|
|
<p>
|
|
Next: <a rel="next" accesskey="n" href="Executing.html#Executing">Executing</a>,
|
|
Previous: <a rel="previous" accesskey="p" href="Introduction.html#Introduction">Introduction</a>,
|
|
Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
|
|
<hr>
|
|
</div>
|
|
|
|
<h2 class="chapter">2 Compiling a Program for Profiling</h2>
|
|
|
|
<p>The first step in generating profile information for your program is
|
|
to compile and link it with profiling enabled.
|
|
|
|
<p>To compile a source file for profiling, specify the ‘<samp><span class="samp">-pg</span></samp>’ option when
|
|
you run the compiler. (This is in addition to the options you normally
|
|
use.)
|
|
|
|
<p>To link the program for profiling, if you use a compiler such as <code>cc</code>
|
|
to do the linking, simply specify ‘<samp><span class="samp">-pg</span></samp>’ in addition to your usual
|
|
options. The same option, ‘<samp><span class="samp">-pg</span></samp>’, alters either compilation or linking
|
|
to do what is necessary for profiling. Here are examples:
|
|
|
|
<pre class="example"> cc -g -c myprog.c utils.c -pg
|
|
cc -o myprog myprog.o utils.o -pg
|
|
</pre>
|
|
<p>The ‘<samp><span class="samp">-pg</span></samp>’ option also works with a command that both compiles and links:
|
|
|
|
<pre class="example"> cc -o myprog myprog.c utils.c -g -pg
|
|
</pre>
|
|
<p>Note: The ‘<samp><span class="samp">-pg</span></samp>’ option must be part of your compilation options
|
|
as well as your link options. If it is not then no call-graph data
|
|
will be gathered and when you run <code>gprof</code> you will get an error
|
|
message like this:
|
|
|
|
<pre class="example"> gprof: gmon.out file is missing call-graph data
|
|
</pre>
|
|
<p>If you add the ‘<samp><span class="samp">-Q</span></samp>’ switch to suppress the printing of the call
|
|
graph data you will still be able to see the time samples:
|
|
|
|
<pre class="example"> Flat profile:
|
|
|
|
Each sample counts as 0.01 seconds.
|
|
% cumulative self self total
|
|
time seconds seconds calls Ts/call Ts/call name
|
|
44.12 0.07 0.07 zazLoop
|
|
35.29 0.14 0.06 main
|
|
20.59 0.17 0.04 bazMillion
|
|
</pre>
|
|
<p>If you run the linker <code>ld</code> directly instead of through a compiler
|
|
such as <code>cc</code>, you may have to specify a profiling startup file
|
|
<samp><span class="file">gcrt0.o</span></samp> as the first input file instead of the usual startup
|
|
file <samp><span class="file">crt0.o</span></samp>. In addition, you would probably want to
|
|
specify the profiling C library, <samp><span class="file">libc_p.a</span></samp>, by writing
|
|
‘<samp><span class="samp">-lc_p</span></samp>’ instead of the usual ‘<samp><span class="samp">-lc</span></samp>’. This is not absolutely
|
|
necessary, but doing this gives you number-of-calls information for
|
|
standard library functions such as <code>read</code> and <code>open</code>. For
|
|
example:
|
|
|
|
<pre class="example"> ld -o myprog /lib/gcrt0.o myprog.o utils.o -lc_p
|
|
</pre>
|
|
<p>If you are running the program on a system which supports shared
|
|
libraries you may run into problems with the profiling support code in
|
|
a shared library being called before that library has been fully
|
|
initialised. This is usually detected by the program encountering a
|
|
segmentation fault as soon as it is run. The solution is to link
|
|
against a static version of the library containing the profiling
|
|
support code, which for <code>gcc</code> users can be done via the
|
|
‘<samp><span class="samp">-static</span></samp>’ or ‘<samp><span class="samp">-static-libgcc</span></samp>’ command line option. For
|
|
example:
|
|
|
|
<pre class="example"> gcc -g -pg -static-libgcc myprog.c utils.c -o myprog
|
|
</pre>
|
|
<p>If you compile only some of the modules of the program with ‘<samp><span class="samp">-pg</span></samp>’, you
|
|
can still profile the program, but you won't get complete information about
|
|
the modules that were compiled without ‘<samp><span class="samp">-pg</span></samp>’. The only information
|
|
you get for the functions in those modules is the total time spent in them;
|
|
there is no record of how many times they were called, or from where. This
|
|
will not affect the flat profile (except that the <code>calls</code> field for
|
|
the functions will be blank), but will greatly reduce the usefulness of the
|
|
call graph.
|
|
|
|
<p>If you wish to perform line-by-line profiling you should use the
|
|
<code>gcov</code> tool instead of <code>gprof</code>. See that tool's manual or
|
|
info pages for more details of how to do this.
|
|
|
|
<p>Note, older versions of <code>gcc</code> produce line-by-line profiling
|
|
information that works with <code>gprof</code> rather than <code>gcov</code> so
|
|
there is still support for displaying this kind of information in
|
|
<code>gprof</code>. See <a href="Line_002dby_002dline.html#Line_002dby_002dline">Line-by-line Profiling</a>.
|
|
|
|
<p>It also worth noting that <code>gcc</code> implements a
|
|
‘<samp><span class="samp">-finstrument-functions</span></samp>’ command line option which will insert
|
|
calls to special user supplied instrumentation routines at the entry
|
|
and exit of every function in their program. This can be used to
|
|
implement an alternative profiling scheme.
|
|
|
|
</body></html>
|
|
|