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| <li class="toctree-l3"><a class="reference internal" href="#get-elf-module-load-address">1. Get ELF Module Load Address</a></li> |
| <li class="toctree-l3"><a class="reference internal" href="#make-the-elf-module-wait-for-you">2. Make the ELF Module Wait for You</a></li> |
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| <li class="toctree-l3"><a class="reference internal" href="#and-debug">5. And Debug</a></li> |
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| <section id="debugging-elf-loadable-modules"> |
| <h1>Debugging ELF Loadable Modules<a class="headerlink" href="#debugging-elf-loadable-modules" title="Permalink to this heading"></a></h1> |
| <div class="admonition warning"> |
| <p class="admonition-title">Warning</p> |
| <p>Migrated from: |
| <a class="reference external" href="https://cwiki.apache.org/confluence/display/NUTTX/Debugging+ELF+Loadable+Modules">https://cwiki.apache.org/confluence/display/NUTTX/Debugging+ELF+Loadable+Modules</a></p> |
| </div> |
| <p>Debugging ELF modules loaded in memory can be tricky because the load address |
| in memory does not match the addresses in the ELF file. This challenge has long |
| existed for debugging uClinux programs and Linux kernel modules; the same |
| solution can be used with NuttX ELF files (and probably with NxFLAT modules as |
| well). Below is a summary of one way to approach this:</p> |
| <section id="get-elf-module-load-address"> |
| <h2>1. Get ELF Module Load Address<a class="headerlink" href="#get-elf-module-load-address" title="Permalink to this heading"></a></h2> |
| <p>Put a change in <code class="docutils literal notranslate"><span class="pre">nuttx/binfmt</span></code> so that you print the address where the ELF |
| text was loaded into memory.</p> |
| <p>Turning on BINFMT debug (<code class="docutils literal notranslate"><span class="pre">CONFIG_DEBUG_BINFMT=y</span></code>) should give you the same |
| information, although it may also provide more output than you really want.</p> |
| <p>Alternatively, you could place a <code class="docutils literal notranslate"><span class="pre">printf()</span></code> at the beginning of your <code class="docutils literal notranslate"><span class="pre">main()</span></code> |
| function so that your ELF module can print its own load address. For example, |
| the difference between the address of <code class="docutils literal notranslate"><span class="pre">main()</span></code> in your object file and the |
| address of <code class="docutils literal notranslate"><span class="pre">main()</span></code> at run time reveals the actual load address.</p> |
| </section> |
| <section id="make-the-elf-module-wait-for-you"> |
| <h2>2. Make the ELF Module Wait for You<a class="headerlink" href="#make-the-elf-module-wait-for-you" title="Permalink to this heading"></a></h2> |
| <p>Insert an infinite loop in the <code class="docutils literal notranslate"><span class="pre">main()</span></code> routine of your ELF program. For |
| example:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">volatile</span><span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">waitforme</span><span class="p">;</span> |
| <span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">arc</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">**</span><span class="n">argv</span><span class="p">)</span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">waitforme</span><span class="p">);</span> |
| <span class="w"> </span><span class="p">...</span> |
| </pre></div> |
| </div> |
| <p>When you start the ELF program, you will see where it was loaded in memory, and |
| the ELF program will remain stuck in the infinite loop. It will continue to |
| wait for <code class="docutils literal notranslate"><span class="pre">waitforme</span></code> to become true before proceeding.</p> |
| </section> |
| <section id="start-the-debugger"> |
| <h2>3. Start the Debugger<a class="headerlink" href="#start-the-debugger" title="Permalink to this heading"></a></h2> |
| <p>Start the debugger, connect to the GDB server, and halt the program. If your |
| debugger is well-behaved, it should stop at the infinite loop in <code class="docutils literal notranslate"><span class="pre">main()</span></code>.</p> |
| </section> |
| <section id="load-offset-symbols"> |
| <h2>4. Load Offset Symbols<a class="headerlink" href="#load-offset-symbols" title="Permalink to this heading"></a></h2> |
| <p>Load symbols using the offset where the ELF module was loaded:</p> |
| <div class="highlight-shell notranslate"><div class="highlight"><pre><span></span><span class="o">(</span>gdb<span class="o">)</span><span class="w"> </span>add-symbol-file<span class="w"> </span><myprogram><span class="w"> </span><load-address> |
| </pre></div> |
| </div> |
| <p>Here, <code class="docutils literal notranslate"><span class="pre"><myprogram></span></code> is your ELF file containing symbols, and |
| <code class="docutils literal notranslate"><span class="pre"><load-address></span></code> is the address where the program text was actually loaded (as |
| determined above). Single-step a couple of times and confirm that you are in the |
| infinite loop.</p> |
| </section> |
| <section id="and-debug"> |
| <h2>5. And Debug<a class="headerlink" href="#and-debug" title="Permalink to this heading"></a></h2> |
| <p>Set <code class="docutils literal notranslate"><span class="pre">waitforme</span></code> to a non-zero value. Execution should exit the infinite loop, |
| and now you can debug the ELF program loaded into RAM in the usual way.</p> |
| </section> |
| <section id="an-easier-way"> |
| <h2>An Easier Way?<a class="headerlink" href="#an-easier-way" title="Permalink to this heading"></a></h2> |
| <p>There might be an alternative that allows you to step into the ELF module |
| without modifying the code to include the <code class="docutils literal notranslate"><span class="pre">waitforme</span></code> loop. You could place a |
| breakpoint on the OS function <code class="docutils literal notranslate"><span class="pre">task_start()</span></code>. That function runs before your |
| ELF program starts, so you should be able to single-step from the OS code |
| directly into your loaded ELF application—no changes to the ELF application |
| required.</p> |
| <p>When you step into the application’s <code class="docutils literal notranslate"><span class="pre">main()</span></code>, you have the relocated address |
| of <code class="docutils literal notranslate"><span class="pre">main()</span></code> and can use that address (see step #1) to compute the load offset.</p> |
| </section> |
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