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<a name="Line_002dby_002dline"></a>
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<p>
Next: <a href="Annotated-Source.html#Annotated-Source" accesskey="n" rel="next">Annotated Source</a>, Previous: <a href="Call-Graph.html#Call-Graph" accesskey="p" rel="prev">Call Graph</a>, Up: <a href="Output.html#Output" accesskey="u" rel="up">Output</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<hr>
<a name="Line_002dby_002dline-Profiling"></a>
<h3 class="section">5.3 Line-by-line Profiling</h3>

<p><code>gprof</code>&rsquo;s &lsquo;<samp>-l</samp>&rsquo; option causes the program to perform
<em>line-by-line</em> profiling.  In this mode, histogram
samples are assigned not to functions, but to individual
lines of source code.  This only works with programs compiled with
older versions of the <code>gcc</code> compiler.  Newer versions of <code>gcc</code>
use a different program - <code>gcov</code> - to display line-by-line
profiling information.
</p>
<p>With the older versions of <code>gcc</code> the program usually has to be
compiled with a &lsquo;<samp>-g</samp>&rsquo; option, in addition to &lsquo;<samp>-pg</samp>&rsquo;, in order
to generate debugging symbols for tracking source code lines.
Note, in much older versions of <code>gcc</code> the program had to be
compiled with the &lsquo;<samp>-a</samp>&rsquo; command-line option as well.
</p>
<p>The flat profile is the most useful output table
in line-by-line mode.
The call graph isn&rsquo;t as useful as normal, since
the current version of <code>gprof</code> does not propagate
call graph arcs from source code lines to the enclosing function.
The call graph does, however, show each line of code
that called each function, along with a count.
</p>
<p>Here is a section of <code>gprof</code>&rsquo;s output, without line-by-line profiling.
Note that <code>ct_init</code> accounted for four histogram hits, and
13327 calls to <code>init_block</code>.
</p>
<div class="smallexample">
<pre class="smallexample">Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total
 time   seconds   seconds    calls  us/call  us/call  name
 30.77      0.13     0.04     6335     6.31     6.31  ct_init


		     Call graph (explanation follows)


granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds

index % time    self  children    called     name

                0.00    0.00       1/13496       name_too_long
                0.00    0.00      40/13496       deflate
                0.00    0.00     128/13496       deflate_fast
                0.00    0.00   13327/13496       ct_init
[7]      0.0    0.00    0.00   13496         init_block

</pre></div>

<p>Now let&rsquo;s look at some of <code>gprof</code>&rsquo;s output from the same program run,
this time with line-by-line profiling enabled.  Note that <code>ct_init</code>&rsquo;s
four histogram hits are broken down into four lines of source code&mdash;one hit
occurred on each of lines 349, 351, 382 and 385.  In the call graph,
note how
<code>ct_init</code>&rsquo;s 13327 calls to <code>init_block</code> are broken down
into one call from line 396, 3071 calls from line 384, 3730 calls
from line 385, and 6525 calls from 387.
</p>
<div class="smallexample">
<pre class="smallexample">Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self
 time   seconds   seconds    calls  name
  7.69      0.10     0.01           ct_init (trees.c:349)
  7.69      0.11     0.01           ct_init (trees.c:351)
  7.69      0.12     0.01           ct_init (trees.c:382)
  7.69      0.13     0.01           ct_init (trees.c:385)


		     Call graph (explanation follows)


granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds

  % time    self  children    called     name

            0.00    0.00       1/13496       name_too_long (gzip.c:1440)
            0.00    0.00       1/13496       deflate (deflate.c:763)
            0.00    0.00       1/13496       ct_init (trees.c:396)
            0.00    0.00       2/13496       deflate (deflate.c:727)
            0.00    0.00       4/13496       deflate (deflate.c:686)
            0.00    0.00       5/13496       deflate (deflate.c:675)
            0.00    0.00      12/13496       deflate (deflate.c:679)
            0.00    0.00      16/13496       deflate (deflate.c:730)
            0.00    0.00     128/13496       deflate_fast (deflate.c:654)
            0.00    0.00    3071/13496       ct_init (trees.c:384)
            0.00    0.00    3730/13496       ct_init (trees.c:385)
            0.00    0.00    6525/13496       ct_init (trees.c:387)
[6]  0.0    0.00    0.00   13496         init_block (trees.c:408)

</pre></div>


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