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<a href='https://github.com/akkartik/mu/blob/master/035compute_segment_address.cc'>https://github.com/akkartik/mu/blob/master/035compute_segment_address.cc</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="Comment">//: ELF binaries have finicky rules about the precise alignment each segment</span>
<span id="L2" class="LineNr"> 2 </span><span class="Comment">//: should start at. They depend on the amount of code in a program.</span>
<span id="L3" class="LineNr"> 3 </span><span class="Comment">//: We shouldn't expect people to adjust segment addresses everytime they make</span>
<span id="L4" class="LineNr"> 4 </span><span class="Comment">//: a change to their programs.</span>
<span id="L5" class="LineNr"> 5 </span><span class="Comment">//: Let's start taking the given segment addresses as guidelines, and adjust</span>
<span id="L6" class="LineNr"> 6 </span><span class="Comment">//: them as necessary.</span>
<span id="L7" class="LineNr"> 7 </span><span class="Comment">//: This gives up a measure of control in placing code and data.</span>
<span id="L8" class="LineNr"> 8 </span>
<span id="L9" class="LineNr"> 9 </span><span class="Normal">void</span> <a href='035compute_segment_address.cc.html#L9'>test_segment_name</a><span class="Delimiter">()</span> <span class="Delimiter">{</span>
<span id="L10" class="LineNr">10 </span>  <a href='011run.cc.html#L82'>run</a><span class="Delimiter">(</span>
<span id="L11" class="LineNr">11 </span>      <span class="Constant">&quot;== code 0x09000000\n&quot;</span>
<span id="L12" class="LineNr">12 </span>      <span class="Constant">&quot;05/add-to-EAX  0x0d0c0b0a/imm32\n&quot;</span>
<span id="L13" class="LineNr">13 </span>      <span class="Comment">// code starts at 0x09000000 + p_offset, which is 0x54 for a single-segment binary</span>
<span id="L14" class="LineNr">14 </span>  <span class="Delimiter">);</span>
<span id="L15" class="LineNr">15 </span>  <a href='003trace.cc.html#L292'>CHECK_TRACE_CONTENTS</a><span class="Delimiter">(</span>
<span id="L16" class="LineNr">16 </span>      <span class="Constant">&quot;load: 0x09000054 -&gt; 05\n&quot;</span>
<span id="L17" class="LineNr">17 </span>      <span class="Constant">&quot;load: 0x09000055 -&gt; 0a\n&quot;</span>
<span id="L18" class="LineNr">18 </span>      <span class="Constant">&quot;load: 0x09000056 -&gt; 0b\n&quot;</span>
<span id="L19" class="LineNr">19 </span>      <span class="Constant">&quot;load: 0x09000057 -&gt; 0c\n&quot;</span>
<span id="L20" class="LineNr">20 </span>      <span class="Constant">&quot;load: 0x09000058 -&gt; 0d\n&quot;</span>
<span id="L21" class="LineNr">21 </span>      <span class="Constant">&quot;run: add imm32 0x0d0c0b0a to EAX\n&quot;</span>
<span id="L22" class="LineNr">22 </span>      <span class="Constant">&quot;run: storing 0x0d0c0b0a\n&quot;</span>
<span id="L23" class="LineNr">23 </span>  <span class="Delimiter">);</span>
<span id="L24" class="LineNr">24 </span><span class="Delimiter">}</span>
<span id="L25" class="LineNr">25 </span>
<span id="L26" class="LineNr">26 </span><span class="Comment">//: compute segment address</span>
<span id="L27" class="LineNr">27 </span>
<span id="L28" class="LineNr">28 </span><span class="Delimiter">:(before &quot;End Transforms&quot;)</span>
<span id="L29" class="LineNr">29 </span><span class="Special"><a href='031transforms.cc.html#L4'>Transform</a></span><span class="Delimiter">.</span>push_back<span class="Delimiter">(</span><a href='035compute_segment_address.cc.html#L32'>compute_segment_starts</a><span class="Delimiter">);</span>
<span id="L30" class="LineNr">30 </span>
<span id="L31" class="LineNr">31 </span><span class="Delimiter">:(code)</span>
<span id="L32" class="LineNr">32 </span><span class="Normal">void</span> <a href='035compute_segment_address.cc.html#L32'>compute_segment_starts</a><span class="Delimiter">(</span>program&amp; p<span class="Delimiter">)</span> <span class="Delimiter">{</span>
<span id="L33" class="LineNr">33 </span>  <a href='003trace.cc.html#L96'>trace</a><span class="Delimiter">(</span><span class="Constant">3</span><span class="Delimiter">,</span> <span class="Constant">&quot;transform&quot;</span><span class="Delimiter">)</span> &lt;&lt; <span class="Constant">&quot;-- compute segment addresses&quot;</span> &lt;&lt; end<span class="Delimiter">();</span>
<span id="L34" class="LineNr">34 </span>  <span class="Normal">uint32_t</span> p_offset = <span class="Comment">/*</span><span class="Comment">size of ehdr</span><span class="Comment">*/</span><span class="Constant">0x34</span> + <a href='001help.cc.html#L170'>SIZE</a><span class="Delimiter">(</span>p<span class="Delimiter">.</span><a href='011run.cc.html#L106'>segments</a><span class="Delimiter">)</span>*<span class="Constant">0x20</span><span class="Comment">/*</span><span class="Comment">size of each phdr</span><span class="Comment">*/</span><span class="Delimiter">;</span>
<span id="L35" class="LineNr">35 </span>  <span class="Normal">for</span> <span class="Delimiter">(</span><span class="Normal">size_t</span> i = <span class="Constant">0</span><span class="Delimiter">;</span>  i &lt; p<span class="Delimiter">.</span><a href='011run.cc.html#L106'>segments</a><span class="Delimiter">.</span>size<span class="Delimiter">();</span>  ++i<span class="Delimiter">)</span> <span class="Delimiter">{</span>
<span id="L36" class="LineNr">36 </span>    segment&amp; curr = p<span class="Delimiter">.</span><a href='011run.cc.html#L106'>segments</a><span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">);</span>
<span id="L37" class="LineNr">37 </span>    <span class="Normal">if</span> <span class="Delimiter">(</span>curr<span class="Delimiter">.</span>start &gt;= <span class="Constant">0x08000000</span><span class="Delimiter">)</span> <span class="Delimiter">{</span>
<span id="L38" class="LineNr">38 </span>      <span class="Comment">// valid address for user space, so assume we're creating a real ELF binary, not just running a test</span>
<span id="L39" class="LineNr">39 </span>      curr<span class="Delimiter">.</span>start &amp;= <span class="Constant">0xfffff000</span><span class="Delimiter">;</span>  <span class="Comment">// same number of zeros as the p_align used when emitting the ELF binary</span>
<span id="L40" class="LineNr">40 </span>      curr<span class="Delimiter">.</span>start |= <span class="Delimiter">(</span>p_offset &amp; <span class="Constant">0xfff</span><span class="Delimiter">);</span>
<span id="L41" class="LineNr">41 </span>      <a href='003trace.cc.html#L96'>trace</a><span class="Delimiter">(</span><span class="Constant">99</span><span class="Delimiter">,</span> <span class="Constant">&quot;transform&quot;</span><span class="Delimiter">)</span> &lt;&lt; <span class="Constant">&quot;segment &quot;</span> &lt;&lt; i &lt;&lt; <span class="Constant">&quot; begins at address 0x&quot;</span> &lt;&lt; <a href='010---vm.cc.html#L395'>HEXWORD</a> &lt;&lt; curr<span class="Delimiter">.</span>start &lt;&lt; end<span class="Delimiter">();</span>
<span id="L42" class="LineNr">42 </span>    <span class="Delimiter">}</span>
<span id="L43" class="LineNr">43 </span>    p_offset += size_of<span class="Delimiter">(</span>curr<span class="Delimiter">);</span>
<span id="L44" class="LineNr">44 </span>    assert<span class="Delimiter">(</span>p_offset &lt; <a href='010---vm.cc.html#L89'>SEGMENT_ALIGNMENT</a><span class="Delimiter">);</span>  <span class="Comment">// for now we get less and less available space in each successive segment</span>
<span id="L45" class="LineNr">45 </span>  <span class="Delimiter">}</span>
<span id="L46" class="LineNr">46 </span><span class="Delimiter">}</span>
<span id="L47" class="LineNr">47 </span>
<span id="L48" class="LineNr">48 </span><span class="Normal">uint32_t</span> size_of<span class="Delimiter">(</span><span class="Normal">const</span> segment&amp; s<span class="Delimiter">)</span> <span class="Delimiter">{</span>
<span id="L49" class="LineNr">49 </span>  <span class="Normal">uint32_t</span> sum = <span class="Constant">0</span><span class="Delimiter">;</span>
<span id="L50" class="LineNr">50 </span>  <span class="Normal">for</span> <span class="Delimiter">(</span><span class="Normal">int</span> i = <span class="Constant">0</span><span class="Delimiter">;</span>  i &lt; <a href='001help.cc.html#L170'>SIZE</a><span class="Delimiter">(</span>s<span class="Delimiter">.</span><a href='011run.cc.html#L113'>lines</a><span class="Delimiter">);</span>  ++i<span class="Delimiter">)</span>
<span id="L51" class="LineNr">51 </span>    sum += <a href='035compute_segment_address.cc.html#L56'>num_bytes</a><span class="Delimiter">(</span>s<span class="Delimiter">.</span><a href='011run.cc.html#L113'>lines</a><span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">));</span>
<span id="L52" class="LineNr">52 </span>  <span class="Identifier">return</span> sum<span class="Delimiter">;</span>
<span id="L53" class="LineNr">53 </span><span class="Delimiter">}</span>
<span id="L54" class="LineNr">54 </span>
<span id="L55" class="LineNr">55 </span><span class="Comment">// Assumes all bitfields are packed.</span>
<span id="L56" class="LineNr">56 </span><span class="Normal">uint32_t</span> <a href='035compute_segment_address.cc.html#L56'>num_bytes</a><span class="Delimiter">(</span><span class="Normal">const</span> line&amp; inst<span class="Delimiter">)</span> <span class="Delimiter">{</span>
<span id="L57" class="LineNr">57 </span>  <span class="Normal">uint32_t</span> sum = <span class="Constant">0</span><span class="Delimiter">;</span>
<span id="L58" class="LineNr">58 </span>  <span class="Normal">for</span> <span class="Delimiter">(</span><span class="Normal">int</span> i = <span class="Constant">0</span><span class="Delimiter">;</span>  i &lt; <a href='001help.cc.html#L170'>SIZE</a><span class="Delimiter">(</span>inst<span class="Delimiter">.</span><a href='011run.cc.html#L122'>words</a><span class="Delimiter">);</span>  ++i<span class="Delimiter">)</span>
<span id="L59" class="LineNr">59 </span>    sum += size_of<span class="Delimiter">(</span>inst<span class="Delimiter">.</span><a href='011run.cc.html#L122'>words</a><span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">));</span>
<span id="L60" class="LineNr">60 </span>  <span class="Identifier">return</span> sum<span class="Delimiter">;</span>
<span id="L61" class="LineNr">61 </span><span class="Delimiter">}</span>
<span id="L62" class="LineNr">62 </span>
<span id="L63" class="LineNr">63 </span><span class="Normal">int</span> size_of<span class="Delimiter">(</span><span class="Normal">const</span> word&amp; w<span class="Delimiter">)</span> <span class="Delimiter">{</span>
<span id="L64" class="LineNr">64 </span>  <span class="Normal">if</span> <span class="Delimiter">(</span>has_operand_metadata<span class="Delimiter">(</span>w<span class="Delimiter">,</span> <span class="Constant">&quot;disp32&quot;</span><span class="Delimiter">)</span> || has_operand_metadata<span class="Delimiter">(</span>w<span class="Delimiter">,</span> <span class="Constant">&quot;imm32&quot;</span><span class="Delimiter">))</span>
<span id="L65" class="LineNr">65 </span>    <span class="Identifier">return</span> <span class="Constant">4</span><span class="Delimiter">;</span>
<span id="L66" class="LineNr">66 </span>  <span class="Normal">else</span> <span class="Normal">if</span> <span class="Delimiter">(</span>has_operand_metadata<span class="Delimiter">(</span>w<span class="Delimiter">,</span> <span class="Constant">&quot;disp16&quot;</span><span class="Delimiter">))</span>
<span id="L67" class="LineNr">67 </span>    <span class="Identifier">return</span> <span class="Constant">2</span><span class="Delimiter">;</span>
<span id="L68" class="LineNr">68 </span>  <span class="Comment">// End size_of(word w) Special-cases</span>
<span id="L69" class="LineNr">69 </span>  <span class="Normal">else</span>
<span id="L70" class="LineNr">70 </span>    <span class="Identifier">return</span> <span class="Constant">1</span><span class="Delimiter">;</span>
<span id="L71" class="LineNr">71 </span><span class="Delimiter">}</span>
<span id="L72" class="LineNr">72 </span>
<span id="L73" class="LineNr">73 </span><span class="Comment">//: Dependencies:</span>
<span id="L74" class="LineNr">74 </span><span class="Comment">//: - We'd like to compute segment addresses before setting up global variables,</span>
<span id="L75" class="LineNr">75 </span><span class="Comment">//:   because computing addresses for global variables requires knowing where</span>
<span id="L76" class="LineNr">76 </span><span class="Comment">//:   the data segment starts.</span>
<span id="L77" class="LineNr">77 </span><span class="Comment">//: - We'd like to finish expanding labels before computing segment addresses,</span>
<span id="L78" class="LineNr">78 </span><span class="Comment">//:   because it would make computing the sizes of segments more self-contained</span>
<span id="L79" class="LineNr">79 </span><span class="Comment">//:   (num_bytes).</span>
<span id="L80" class="LineNr">80 </span><span class="Comment">//:</span>
<span id="L81" class="LineNr">81 </span><span class="Comment">//: Decision: compute segment addresses before expanding labels, by being</span>
<span id="L82" class="LineNr">82 </span><span class="Comment">//: aware in this layer of certain operand types that will eventually occupy</span>
<span id="L83" class="LineNr">83 </span><span class="Comment">//: multiple bytes.</span>
<span id="L84" class="LineNr">84 </span><span class="Comment">//:</span>
<span id="L85" class="LineNr">85 </span><span class="Comment">//: The layer to expand labels later hooks into num_bytes() to teach this</span>
<span id="L86" class="LineNr">86 </span><span class="Comment">//: layer that labels occupy zero space in the binary.</span>
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