1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- This file documents the gprof profiler of the GNU system. 4 5Copyright (C) 1988-2021 Free Software Foundation, Inc. 6 7Permission is granted to copy, distribute and/or modify this document 8under the terms of the GNU Free Documentation License, Version 1.3 9or any later version published by the Free Software Foundation; 10with no Invariant Sections, with no Front-Cover Texts, and with no 11Back-Cover Texts. A copy of the license is included in the 12section entitled "GNU Free Documentation License". 13 --> 14<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> 15<head> 16<title>GNU gprof: Compiling</title> 17 18<meta name="description" content="GNU gprof: Compiling"> 19<meta name="keywords" content="GNU gprof: Compiling"> 20<meta name="resource-type" content="document"> 21<meta name="distribution" content="global"> 22<meta name="Generator" content="makeinfo"> 23<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 24<link href="index.html#Top" rel="start" title="Top"> 25<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> 26<link href="index.html#Top" rel="up" title="Top"> 27<link href="Executing.html#Executing" rel="next" title="Executing"> 28<link href="Introduction.html#Introduction" rel="previous" title="Introduction"> 29<style type="text/css"> 30<!-- 31a.summary-letter {text-decoration: none} 32blockquote.smallquotation {font-size: smaller} 33div.display {margin-left: 3.2em} 34div.example {margin-left: 3.2em} 35div.indentedblock {margin-left: 3.2em} 36div.lisp {margin-left: 3.2em} 37div.smalldisplay {margin-left: 3.2em} 38div.smallexample {margin-left: 3.2em} 39div.smallindentedblock {margin-left: 3.2em; font-size: smaller} 40div.smalllisp {margin-left: 3.2em} 41kbd {font-style:oblique} 42pre.display {font-family: inherit} 43pre.format {font-family: inherit} 44pre.menu-comment {font-family: serif} 45pre.menu-preformatted {font-family: serif} 46pre.smalldisplay {font-family: inherit; font-size: smaller} 47pre.smallexample {font-size: smaller} 48pre.smallformat {font-family: inherit; font-size: smaller} 49pre.smalllisp {font-size: smaller} 50span.nocodebreak {white-space:nowrap} 51span.nolinebreak {white-space:nowrap} 52span.roman {font-family:serif; font-weight:normal} 53span.sansserif {font-family:sans-serif; font-weight:normal} 54ul.no-bullet {list-style: none} 55--> 56</style> 57 58 59</head> 60 61<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> 62<a name="Compiling"></a> 63<div class="header"> 64<p> 65Next: <a href="Executing.html#Executing" accesskey="n" rel="next">Executing</a>, Previous: <a href="Introduction.html#Introduction" accesskey="p" rel="previous">Introduction</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> 66</div> 67<hr> 68<a name="Compiling-a-Program-for-Profiling"></a> 69<h2 class="chapter">2 Compiling a Program for Profiling</h2> 70 71<p>The first step in generating profile information for your program is 72to compile and link it with profiling enabled. 73</p> 74<p>To compile a source file for profiling, specify the ‘<samp>-pg</samp>’ option when 75you run the compiler. (This is in addition to the options you normally 76use.) 77</p> 78<p>To link the program for profiling, if you use a compiler such as <code>cc</code> 79to do the linking, simply specify ‘<samp>-pg</samp>’ in addition to your usual 80options. The same option, ‘<samp>-pg</samp>’, alters either compilation or linking 81to do what is necessary for profiling. Here are examples: 82</p> 83<div class="example"> 84<pre class="example">cc -g -c myprog.c utils.c -pg 85cc -o myprog myprog.o utils.o -pg 86</pre></div> 87 88<p>The ‘<samp>-pg</samp>’ option also works with a command that both compiles and links: 89</p> 90<div class="example"> 91<pre class="example">cc -o myprog myprog.c utils.c -g -pg 92</pre></div> 93 94<p>Note: The ‘<samp>-pg</samp>’ option must be part of your compilation options 95as well as your link options. If it is not then no call-graph data 96will be gathered and when you run <code>gprof</code> you will get an error 97message like this: 98</p> 99<div class="example"> 100<pre class="example">gprof: gmon.out file is missing call-graph data 101</pre></div> 102 103<p>If you add the ‘<samp>-Q</samp>’ switch to suppress the printing of the call 104graph data you will still be able to see the time samples: 105</p> 106<div class="example"> 107<pre class="example">Flat profile: 108 109Each sample counts as 0.01 seconds. 110 % cumulative self self total 111 time seconds seconds calls Ts/call Ts/call name 112 44.12 0.07 0.07 zazLoop 113 35.29 0.14 0.06 main 114 20.59 0.17 0.04 bazMillion 115</pre></div> 116 117<p>If you run the linker <code>ld</code> directly instead of through a compiler 118such as <code>cc</code>, you may have to specify a profiling startup file 119<samp>gcrt0.o</samp> as the first input file instead of the usual startup 120file <samp>crt0.o</samp>. In addition, you would probably want to 121specify the profiling C library, <samp>libc_p.a</samp>, by writing 122‘<samp>-lc_p</samp>’ instead of the usual ‘<samp>-lc</samp>’. This is not absolutely 123necessary, but doing this gives you number-of-calls information for 124standard library functions such as <code>read</code> and <code>open</code>. For 125example: 126</p> 127<div class="example"> 128<pre class="example">ld -o myprog /lib/gcrt0.o myprog.o utils.o -lc_p 129</pre></div> 130 131<p>If you are running the program on a system which supports shared 132libraries you may run into problems with the profiling support code in 133a shared library being called before that library has been fully 134initialised. This is usually detected by the program encountering a 135segmentation fault as soon as it is run. The solution is to link 136against a static version of the library containing the profiling 137support code, which for <code>gcc</code> users can be done via the 138‘<samp>-static</samp>’ or ‘<samp>-static-libgcc</samp>’ command-line option. For 139example: 140</p> 141<div class="example"> 142<pre class="example">gcc -g -pg -static-libgcc myprog.c utils.c -o myprog 143</pre></div> 144 145<p>If you compile only some of the modules of the program with ‘<samp>-pg</samp>’, you 146can still profile the program, but you won’t get complete information about 147the modules that were compiled without ‘<samp>-pg</samp>’. The only information 148you get for the functions in those modules is the total time spent in them; 149there is no record of how many times they were called, or from where. This 150will not affect the flat profile (except that the <code>calls</code> field for 151the functions will be blank), but will greatly reduce the usefulness of the 152call graph. 153</p> 154<p>If you wish to perform line-by-line profiling you should use the 155<code>gcov</code> tool instead of <code>gprof</code>. See that tool’s manual or 156info pages for more details of how to do this. 157</p> 158<p>Note, older versions of <code>gcc</code> produce line-by-line profiling 159information that works with <code>gprof</code> rather than <code>gcov</code> so 160there is still support for displaying this kind of information in 161<code>gprof</code>. See <a href="Line_002dby_002dline.html#Line_002dby_002dline">Line-by-line Profiling</a>. 162</p> 163<p>It also worth noting that <code>gcc</code> implements a 164‘<samp>-finstrument-functions</samp>’ command-line option which will insert 165calls to special user supplied instrumentation routines at the entry 166and exit of every function in their program. This can be used to 167implement an alternative profiling scheme. 168</p> 169<hr> 170<div class="header"> 171<p> 172Next: <a href="Executing.html#Executing" accesskey="n" rel="next">Executing</a>, Previous: <a href="Introduction.html#Introduction" accesskey="p" rel="previous">Introduction</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> 173</div> 174 175 176 177</body> 178</html> 179