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<a name="Debugging-the-Analyzer"></a>
<div class="header">
<p>
Previous: <a href="Analyzer-Internals.html#Analyzer-Internals" accesskey="p" rel="previous">Analyzer Internals</a>, Up: <a href="Static-Analyzer.html#Static-Analyzer" accesskey="u" rel="up">Static Analyzer</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Debugging-the-Analyzer-1"></a>
<h3 class="section">27.2 Debugging the Analyzer</h3>
<a name="index-analyzer_002c-debugging"></a>
<a name="index-static-analyzer_002c-debugging"></a>
<p>When debugging the analyzer I normally use all of these options
together:
</p>
<div class="smallexample">
<pre class="smallexample">./xgcc -B. \
-S \
-fanalyzer \
OTHER_GCC_ARGS \
-wrapper gdb,--args \
-fdump-analyzer-stderr \
-fanalyzer-fine-grained \
-fdump-ipa-analyzer=stderr
</pre></div>
<p>where:
</p>
<ul>
<li> <code>./xgcc -B.</code>
is the usual way to invoke a self-built GCC from within the <samp>BUILDDIR/gcc</samp>
subdirectory.
</li><li> <code>-S</code>
so that the driver (<code>./xgcc</code>) invokes <code>cc1</code>, but doesn’t bother
running the assembler or linker (since the analyzer runs inside <code>cc1</code>).
</li><li> <code>-fanalyzer</code>
enables the analyzer, obviously.
</li><li> <code>-wrapper gdb,--args</code>
invokes <code>cc1</code> under the debugger so that I can debug <code>cc1</code> and
set breakpoints and step through things.
</li><li> <code>-fdump-analyzer-stderr</code>
so that the logging interface is enabled and goes to stderr, which often
gives valuable context into what’s happening when stepping through the
analyzer
</li><li> <code>-fanalyzer-fine-grained</code>
which splits the effect of every statement into its own
exploded_node, rather than the default (which tries to combine
successive stmts to reduce the size of the exploded_graph). This makes
it easier to see exactly where a particular change happens.
</li><li> <code>-fdump-ipa-analyzer=stderr</code>
which dumps the GIMPLE IR seen by the analyzer pass to stderr
</li></ul>
<p>Other useful options:
</p>
<ul>
<li> <code>-fdump-analyzer-exploded-graph</code>
which dumps a <samp>SRC.eg.dot</samp> GraphViz file that I can look at (with
python-xdot)
</li><li> <code>-fdump-analyzer-exploded-nodes-2</code>
which dumps a <samp>SRC.eg.txt</samp> file containing the full <code>exploded_graph</code>.
</li></ul>
<p>Assuming that you have the
<a href="https://gcc-newbies-guide.readthedocs.io/en/latest/debugging.html">python support scripts for gdb</a>
installed, you can use:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) break-on-saved-diagnostic
</pre></div>
<p>to put a breakpoint at the place where a diagnostic is saved during
<code>exploded_graph</code> exploration, to see where a particular diagnostic
is being saved, and:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) break-on-diagnostic
</pre></div>
<p>to put a breakpoint at the place where diagnostics are actually emitted.
</p>
<a name="Special-Functions-for-Debugging-the-Analyzer"></a>
<h4 class="subsection">27.2.1 Special Functions for Debugging the Analyzer</h4>
<p>The analyzer recognizes various special functions by name, for use
in debugging the analyzer, and for use in DejaGnu tests.
</p>
<p>The declarations of these functions can be seen in the testsuite
in <samp>analyzer-decls.h</samp>. None of these functions are actually
implemented in terms of code, merely as <code>known_function</code> subclasses
(in <samp>gcc/analyzer/kf-analyzer.cc</samp>).
</p>
<dl compact="compact">
<dt><code>__analyzer_break</code></dt>
<dd><p>Add:
</p><div class="smallexample">
<pre class="smallexample"> __analyzer_break ();
</pre></div>
<p>to the source being analyzed to trigger a breakpoint in the analyzer when
that source is reached. By putting a series of these in the source, it’s
much easier to effectively step through the program state as it’s analyzed.
</p>
</dd>
<dt><code>__analyzer_describe</code></dt>
<dd><p>The analyzer handles:
</p>
<div class="smallexample">
<pre class="smallexample">__analyzer_describe (0, expr);
</pre></div>
<p>by emitting a warning describing the 2nd argument (which can be of any
type), at a verbosity level given by the 1st argument. This is for use when
debugging, and may be of use in DejaGnu tests.
</p>
</dd>
<dt><code>__analyzer_dump</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">__analyzer_dump ();
</pre></div>
<p>will dump the copious information about the analyzer’s state each time it
reaches the call in its traversal of the source.
</p>
</dd>
<dt><code>__analyzer_dump_capacity</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">extern void __analyzer_dump_capacity (const void *ptr);
</pre></div>
<p>will emit a warning describing the capacity of the base region of
the region pointed to by the 1st argument.
</p>
</dd>
<dt><code>__analyzer_dump_escaped</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">extern void __analyzer_dump_escaped (void);
</pre></div>
<p>will emit a warning giving the number of decls that have escaped on this
analysis path, followed by a comma-separated list of their names,
in alphabetical order.
</p>
</dd>
<dt><code>__analyzer_dump_path</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">__analyzer_dump_path ();
</pre></div>
<p>will emit a placeholder “note” diagnostic with a path to that call site,
if the analyzer finds a feasible path to it. This can be useful for
writing DejaGnu tests for constraint-tracking and feasibility checking.
</p>
</dd>
<dt><code>__analyzer_dump_exploded_nodes</code></dt>
<dd><p>For every callsite to <code>__analyzer_dump_exploded_nodes</code> the analyzer
will emit a warning after it finished the analysis containing information
on all of the exploded nodes at that program point.
</p>
<div class="smallexample">
<pre class="smallexample"> __analyzer_dump_exploded_nodes (0);
</pre></div>
<p>will output the number of “processed” nodes, and the IDs of
both “processed” and “merger” nodes, such as:
</p>
<div class="smallexample">
<pre class="smallexample">warning: 2 processed enodes: [EN: 56, EN: 58] merger(s): [EN: 54-55, EN: 57, EN: 59]
</pre></div>
<p>With a non-zero argument
</p>
<div class="smallexample">
<pre class="smallexample"> __analyzer_dump_exploded_nodes (1);
</pre></div>
<p>it will also dump all of the states within the “processed” nodes.
</p>
</dd>
<dt><code>__analyzer_dump_named_constant</code></dt>
<dd><p>When the analyzer sees a call to <code>__analyzer_dump_named_constant</code> it
will emit a warning describing what is known about the value of a given
named constant, for parts of the analyzer that interact with target
headers.
</p>
<p>For example:
</p>
<div class="smallexample">
<pre class="smallexample">__analyzer_dump_named_constant ("O_RDONLY");
</pre></div>
<p>might lead to the analyzer emitting the warning:
</p>
<div class="smallexample">
<pre class="smallexample">warning: named constant 'O_RDONLY' has value '1'
</pre></div>
</dd>
<dt><code>__analyzer_dump_region_model</code></dt>
<dd><div class="smallexample">
<pre class="smallexample"> __analyzer_dump_region_model ();
</pre></div>
<p>will dump the region_model’s state to stderr.
</p>
</dd>
<dt><code>__analyzer_dump_state</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">__analyzer_dump_state ("malloc", ptr);
</pre></div>
<p>will emit a warning describing the state of the 2nd argument
(which can be of any type) with respect to the state machine with
a name matching the 1st argument (which must be a string literal).
This is for use when debugging, and may be of use in DejaGnu tests.
</p>
</dd>
<dt><code>__analyzer_eval</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">__analyzer_eval (expr);
</pre></div>
<p>will emit a warning with text "TRUE", FALSE" or "UNKNOWN" based on the
truthfulness of the argument. This is useful for writing DejaGnu tests.
</p>
</dd>
<dt><code>__analyzer_get_unknown_ptr</code></dt>
<dd><div class="smallexample">
<pre class="smallexample">__analyzer_get_unknown_ptr ();
</pre></div>
<p>will obtain an unknown <code>void *</code>.
</p>
</dd>
</dl>
<a name="Other-Debugging-Techniques"></a>
<h4 class="subsection">27.2.2 Other Debugging Techniques</h4>
<p>To compare two different exploded graphs, try
<code>-fdump-analyzer-exploded-nodes-2 -fdump-noaddr -fanalyzer-fine-grained</code>.
This will dump a <samp>SRC.eg.txt</samp> file containing the full
<code>exploded_graph</code>. I use <code>diff -u50 -p</code> to compare two different
such files (e.g. before and after a patch) to find the first place where the
two graphs diverge. The option <samp>-fdump-noaddr</samp> will suppress
printing pointers withihn the dumps (which would otherwise hide the real
differences with irrelevent churn).
</p>
<p>The option <samp>-fdump-analyzer-json</samp> will dump both the supergraph
and the exploded graph in compressed JSON form.
</p>
<p>One approach when tracking down where a particular bogus state is
introduced into the <code>exploded_graph</code> is to add custom code to
<code>program_state::validate</code>.
</p>
<p>The debug function <code>region::is_named_decl_p</code> can be used when debugging,
such as for assertions and conditional breakpoints. For example, when
tracking down a bug in handling a decl called <code>yy_buffer_stack</code>, I
temporarily added a:
</p><div class="smallexample">
<pre class="smallexample"> gcc_assert (!m_base_region->is_named_decl_p ("yy_buffer_stack"));
</pre></div>
<p>to <code>binding_cluster::mark_as_escaped</code> to trap a point where
<code>yy_buffer_stack</code> was mistakenly being treated as having escaped.
</p>
<hr>
<div class="header">
<p>
Previous: <a href="Analyzer-Internals.html#Analyzer-Internals" accesskey="p" rel="previous">Analyzer Internals</a>, Up: <a href="Static-Analyzer.html#Static-Analyzer" accesskey="u" rel="up">Static Analyzer</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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