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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 >= 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 >= 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->= $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:nowrap:textwidth=0</span>
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