| <html lang="en"> |
| <head> |
| <title>Annotated Source - 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="up" href="Output.html#Output" title="Output"> |
| <link rel="prev" href="Line_002dby_002dline.html#Line_002dby_002dline" title="Line-by-line"> |
| <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) 1988-2019 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="Annotated-Source"></a> |
| <p> |
| Previous: <a rel="previous" accesskey="p" href="Line_002dby_002dline.html#Line_002dby_002dline">Line-by-line</a>, |
| Up: <a rel="up" accesskey="u" href="Output.html#Output">Output</a> |
| <hr> |
| </div> |
| |
| <h3 class="section">5.4 The Annotated Source Listing</h3> |
| |
| <p><code>gprof</code>'s ‘<samp><span class="samp">-A</span></samp>’ option triggers an annotated source listing, |
| which lists the program's source code, each function labeled with the |
| number of times it was called. You may also need to specify the |
| ‘<samp><span class="samp">-I</span></samp>’ option, if <code>gprof</code> can't find the source code files. |
| |
| <p>With older versions of <code>gcc</code> compiling with ‘<samp><span class="samp">gcc ... -g |
| -pg -a</span></samp>’ augments your program with basic-block counting code, in |
| addition to function counting code. This enables <code>gprof</code> to |
| determine how many times each line of code was executed. With newer |
| versions of <code>gcc</code> support for displaying basic-block counts is |
| provided by the <code>gcov</code> program. |
| |
| <p>For example, consider the following function, taken from gzip, |
| with line numbers added: |
| |
| <pre class="smallexample"> 1 ulg updcrc(s, n) |
| 2 uch *s; |
| 3 unsigned n; |
| 4 { |
| 5 register ulg c; |
| 6 |
| 7 static ulg crc = (ulg)0xffffffffL; |
| 8 |
| 9 if (s == NULL) { |
| 10 c = 0xffffffffL; |
| 11 } else { |
| 12 c = crc; |
| 13 if (n) do { |
| 14 c = crc_32_tab[...]; |
| 15 } while (--n); |
| 16 } |
| 17 crc = c; |
| 18 return c ^ 0xffffffffL; |
| 19 } |
| |
| </pre> |
| <p><code>updcrc</code> has at least five basic-blocks. |
| One is the function itself. The |
| <code>if</code> statement on line 9 generates two more basic-blocks, one |
| for each branch of the <code>if</code>. A fourth basic-block results from |
| the <code>if</code> on line 13, and the contents of the <code>do</code> loop form |
| the fifth basic-block. The compiler may also generate additional |
| basic-blocks to handle various special cases. |
| |
| <p>A program augmented for basic-block counting can be analyzed with |
| ‘<samp><span class="samp">gprof -l -A</span></samp>’. |
| The ‘<samp><span class="samp">-x</span></samp>’ option is also helpful, |
| to ensure that each line of code is labeled at least once. |
| Here is <code>updcrc</code>'s |
| annotated source listing for a sample <code>gzip</code> run: |
| |
| <pre class="smallexample"> ulg updcrc(s, n) |
| uch *s; |
| unsigned n; |
| 2 ->{ |
| register ulg c; |
| |
| static ulg crc = (ulg)0xffffffffL; |
| |
| 2 -> if (s == NULL) { |
| 1 -> c = 0xffffffffL; |
| 1 -> } else { |
| 1 -> c = crc; |
| 1 -> if (n) do { |
| 26312 -> c = crc_32_tab[...]; |
| 26312,1,26311 -> } while (--n); |
| } |
| 2 -> crc = c; |
| 2 -> return c ^ 0xffffffffL; |
| 2 ->} |
| </pre> |
| <p>In this example, the function was called twice, passing once through |
| each branch of the <code>if</code> statement. The body of the <code>do</code> |
| loop was executed a total of 26312 times. Note how the <code>while</code> |
| statement is annotated. It began execution 26312 times, once for |
| each iteration through the loop. One of those times (the last time) |
| it exited, while it branched back to the beginning of the loop 26311 times. |
| |
| </body></html> |
| |
