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- <a name="Annotated-Source"></a>
- <div class="header">
- <p>
- Previous: <a href="Line_002dby_002dline.html#Line_002dby_002dline" accesskey="p" rel="prev">Line-by-line</a>, Up: <a href="Output.html#Output" accesskey="u" rel="up">Output</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
- </div>
- <hr>
- <a name="The-Annotated-Source-Listing"></a>
- <h3 class="section">5.4 The Annotated Source Listing</h3>
-
- <p><code>gprof</code>’s ‘<samp>-A</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>-I</samp>’ option, if <code>gprof</code> can’t find the source code files.
- </p>
- <p>With older versions of <code>gcc</code> compiling with ‘<samp>gcc … -g
- -pg -a</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>
- <p>For example, consider the following function, taken from gzip,
- with line numbers added:
- </p>
- <div class="smallexample">
- <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></div>
-
- <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>
- <p>A program augmented for basic-block counting can be analyzed with
- ‘<samp>gprof -l -A</samp>’.
- The ‘<samp>-x</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:
- </p>
- <div class="smallexample">
- <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></div>
-
- <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.
- </p>
- <hr>
- <div class="header">
- <p>
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