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<a href='https://github.com/akkartik/mu/blob/main/baremetal/120allocate.subx'>https://github.com/akkartik/mu/blob/main/baremetal/120allocate.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment">#   instruction                     effective address                                                   register    displacement    immediate</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxS1Comment"># . op          subop               mod             rm32          base        index         scale       r32</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxS1Comment"># . 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes</span>
<span id="L4" class="LineNr"> 4 </span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># Fill a region of memory with zeroes.</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxFunction">zero-out</span>:  <span class="subxComment"># start: (addr byte), size: int</span>
<span id="L7" class="LineNr"> 7 </span>    <span class="subxComment"># pseudocode:</span>
<span id="L8" class="LineNr"> 8 </span>    <span class="subxComment">#   curr/esi = start</span>
<span id="L9" class="LineNr"> 9 </span>    <span class="subxComment">#   i/ecx = 0</span>
<span id="L10" class="LineNr">10 </span>    <span class="subxComment">#   while true</span>
<span id="L11" class="LineNr">11 </span>    <span class="subxComment">#     if (i &gt;= size) break</span>
<span id="L12" class="LineNr">12 </span>    <span class="subxComment">#     *curr = 0</span>
<span id="L13" class="LineNr">13 </span>    <span class="subxComment">#     ++curr</span>
<span id="L14" class="LineNr">14 </span>    <span class="subxComment">#     ++i</span>
<span id="L15" class="LineNr">15 </span>    <span class="subxComment">#</span>
<span id="L16" class="LineNr">16 </span>    <span class="subxS1Comment"># . prologue</span>
<span id="L17" class="LineNr">17 </span>    55/push-ebp
<span id="L18" class="LineNr">18 </span>    89/copy                         3/mod/direct    5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          4/r32/esp  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy esp to ebp</span>
<span id="L19" class="LineNr">19 </span>    <span class="subxS1Comment"># . save registers</span>
<span id="L20" class="LineNr">20 </span>    50/push-eax
<span id="L21" class="LineNr">21 </span>    51/push-ecx
<span id="L22" class="LineNr">22 </span>    52/push-edx
<span id="L23" class="LineNr">23 </span>    56/push-esi
<span id="L24" class="LineNr">24 </span>    <span class="subxComment"># curr/esi = start</span>
<span id="L25" class="LineNr">25 </span>    8b/copy                         1/mod/*+disp8   5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          6/r32/esi   8/disp8        <span class="Normal"> . </span>                <span class="subxComment"># copy *(ebp+8) to esi</span>
<span id="L26" class="LineNr">26 </span>    <span class="subxComment"># var i/ecx: int = 0</span>
<span id="L27" class="LineNr">27 </span>    31/xor                          3/mod/direct    1/rm32/ecx   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          1/r32/ecx  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># clear ecx</span>
<span id="L28" class="LineNr">28 </span>    <span class="subxComment"># edx = size</span>
<span id="L29" class="LineNr">29 </span>    8b/copy                         1/mod/*+disp8   5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          2/r32/edx   0xc/disp8      <span class="Normal"> . </span>                <span class="subxComment"># copy *(ebp+12) to edx</span>
<span id="L30" class="LineNr">30 </span><span class="Constant">$zero-out:loop</span>:
<span id="L31" class="LineNr">31 </span>    <span class="subxComment"># if (i &gt;= size) break</span>
<span id="L32" class="LineNr">32 </span>    39/compare                      3/mod/direct    1/rm32/ecx   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          2/r32/edx  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># compare ecx with edx</span>
<span id="L33" class="LineNr">33 </span>    7d/jump-if-&gt;=  $zero-out:end/disp8
<span id="L34" class="LineNr">34 </span>    <span class="subxComment"># *curr = 0</span>
<span id="L35" class="LineNr">35 </span>    c6          0/subop/copy-byte   0/mod/direct    6/rm32/esi   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>         <span class="Normal"> . </span>         <span class="Normal"> . </span>              0/imm8            <span class="subxComment"># copy byte to *esi</span>
<span id="L36" class="LineNr">36 </span>    <span class="subxComment"># ++curr</span>
<span id="L37" class="LineNr">37 </span>    46/increment-esi
<span id="L38" class="LineNr">38 </span>    <span class="subxComment"># ++i</span>
<span id="L39" class="LineNr">39 </span>    41/increment-ecx
<span id="L40" class="LineNr">40 </span>    eb/jump  $zero-out:<span class="Constant">loop</span>/disp8
<span id="L41" class="LineNr">41 </span><span class="Constant">$zero-out:end</span>:
<span id="L42" class="LineNr">42 </span>    <span class="subxS1Comment"># . restore registers</span>
<span id="L43" class="LineNr">43 </span>    5e/pop-to-esi
<span id="L44" class="LineNr">44 </span>    5a/pop-to-edx
<span id="L45" class="LineNr">45 </span>    59/pop-to-ecx
<span id="L46" class="LineNr">46 </span>    58/pop-to-eax
<span id="L47" class="LineNr">47 </span>    <span class="subxS1Comment"># . epilogue</span>
<span id="L48" class="LineNr">48 </span>    89/copy                         3/mod/direct    4/rm32/esp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          5/r32/ebp  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy ebp to esp</span>
<span id="L49" class="LineNr">49 </span>    5d/pop-to-ebp
<span id="L50" class="LineNr">50 </span>    c3/return
<span id="L51" class="LineNr">51 </span>
<span id="L52" class="LineNr">52 </span><span class="subxS2Comment"># . . vim&#0058;nowrap:textwidth=0</span>
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