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<a href='https://github.com/akkartik/mu/blob/master/076zero-out.subx'>https://github.com/akkartik/mu/blob/master/076zero-out.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Fill a region of memory with zeroes.</span>
<span id="L2" class="LineNr"> 2 </span>
<span id="L3" class="LineNr"> 3 </span>== code
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># instruction effective address register displacement immediate</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxS1Comment"># . op subop mod rm32 base index scale r32</span>
<span id="L6" class="LineNr"> 6 </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="L7" class="LineNr"> 7 </span>
<span id="L8" class="LineNr"> 8 </span><span class="subxFunction">zero-out</span>: <span class="subxComment"># start : address, len : int</span>
<span id="L9" class="LineNr"> 9 </span> <span class="subxComment"># pseudocode:</span>
<span id="L10" class="LineNr">10 </span> <span class="subxComment"># curr/ESI = start</span>
<span id="L11" class="LineNr">11 </span> <span class="subxComment"># i/ECX = 0</span>
<span id="L12" class="LineNr">12 </span> <span class="subxComment"># while true</span>
<span id="L13" class="LineNr">13 </span> <span class="subxComment"># if (i >= len) break</span>
<span id="L14" class="LineNr">14 </span> <span class="subxComment"># *curr = 0</span>
<span id="L15" class="LineNr">15 </span> <span class="subxComment"># ++curr</span>
<span id="L16" class="LineNr">16 </span> <span class="subxComment"># ++i</span>
<span id="L17" class="LineNr">17 </span> <span class="subxComment">#</span>
<span id="L18" class="LineNr">18 </span> <span class="subxS1Comment"># . prolog</span>
<span id="L19" class="LineNr">19 </span> 55/push-EBP
<span id="L20" class="LineNr">20 </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="L21" class="LineNr">21 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L22" class="LineNr">22 </span> 50/push-EAX
<span id="L23" class="LineNr">23 </span> 51/push-ECX
<span id="L24" class="LineNr">24 </span> 52/push-EDX
<span id="L25" class="LineNr">25 </span> 56/push-ESI
<span id="L26" class="LineNr">26 </span> <span class="subxComment"># curr/ESI = start</span>
<span id="L27" class="LineNr">27 </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="L28" class="LineNr">28 </span> <span class="subxComment"># i/ECX = 0</span>
<span id="L29" class="LineNr">29 </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="L30" class="LineNr">30 </span> <span class="subxComment"># EDX = len</span>
<span id="L31" class="LineNr">31 </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="L32" class="LineNr">32 </span><span class="Constant">$zero-out:loop</span>:
<span id="L33" class="LineNr">33 </span> <span class="subxComment"># if (i >= len) break</span>
<span id="L34" class="LineNr">34 </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="L35" class="LineNr">35 </span> 7d/jump-if-greater-or-equal $zero-out:end/disp8
<span id="L36" class="LineNr">36 </span> <span class="subxComment"># *curr = 0</span>
<span id="L37" class="LineNr">37 </span> c6 0/subop/copy 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="L38" class="LineNr">38 </span> <span class="subxComment"># ++curr</span>
<span id="L39" class="LineNr">39 </span> 46/increment-ESI
<span id="L40" class="LineNr">40 </span> <span class="subxComment"># ++i</span>
<span id="L41" class="LineNr">41 </span> 41/increment-ECX
<span id="L42" class="LineNr">42 </span> eb/jump $zero-out:loop/disp8
<span id="L43" class="LineNr">43 </span><span class="Constant">$zero-out:end</span>:
<span id="L44" class="LineNr">44 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L45" class="LineNr">45 </span> 5e/pop-to-ESI
<span id="L46" class="LineNr">46 </span> 5a/pop-to-EDX
<span id="L47" class="LineNr">47 </span> 59/pop-to-ECX
<span id="L48" class="LineNr">48 </span> 58/pop-to-EAX
<span id="L49" class="LineNr">49 </span> <span class="subxS1Comment"># . epilog</span>
<span id="L50" class="LineNr">50 </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="L51" class="LineNr">51 </span> 5d/pop-to-EBP
<span id="L52" class="LineNr">52 </span> c3/return
<span id="L53" class="LineNr">53 </span>
<span id="L54" class="LineNr">54 </span><span class="subxTest">test-zero-out</span>:
<span id="L55" class="LineNr">55 </span> <span class="subxS1Comment"># . prolog</span>
<span id="L56" class="LineNr">56 </span> 55/push-EBP
<span id="L57" class="LineNr">57 </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="L58" class="LineNr">58 </span> <span class="subxComment"># region/ECX = 34, 35, 36, 37</span>
<span id="L59" class="LineNr">59 </span> 68/push 0x37363534/imm32
<span id="L60" class="LineNr">60 </span> 89/copy 3/mod/direct 1/rm32/ECX <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 ECX</span>
<span id="L61" class="LineNr">61 </span> <span class="subxComment"># zero-out(ECX, 3)</span>
<span id="L62" class="LineNr">62 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L63" class="LineNr">63 </span> 68/push 3/imm32/len
<span id="L64" class="LineNr">64 </span> 51/push-ECX
<span id="L65" class="LineNr">65 </span> <span class="subxS2Comment"># . . call</span>
<span id="L66" class="LineNr">66 </span> e8/call <a href='076zero-out.subx.html#L8'>zero-out</a>/disp32
<span id="L67" class="LineNr">67 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L68" class="LineNr">68 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 8/imm32 <span class="subxComment"># add to ESP</span>
<span id="L69" class="LineNr">69 </span> <span class="subxComment"># first 3 bytes cleared, fourth left alone</span>
<span id="L70" class="LineNr">70 </span> <span class="subxS1Comment"># . check-ints-equal(*ECX, 0x37000000, msg)</span>
<span id="L71" class="LineNr">71 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L72" class="LineNr">72 </span> 68/push <span class="Constant">"F - test-zero-out"</span>/imm32
<span id="L73" class="LineNr">73 </span> 68/push 0x37000000/imm32
<span id="L74" class="LineNr">74 </span> ff 6/subop/push 0/mod/indirect 1/rm32/ECX <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="subxComment"># push *ECX</span>
<span id="L75" class="LineNr">75 </span> <span class="subxS2Comment"># . . call</span>
<span id="L76" class="LineNr">76 </span> e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32
<span id="L77" class="LineNr">77 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L78" class="LineNr">78 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 0xc/imm32 <span class="subxComment"># add to ESP</span>
<span id="L79" class="LineNr">79 </span> <span class="subxS1Comment"># . epilog</span>
<span id="L80" class="LineNr">80 </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="L81" class="LineNr">81 </span> 5d/pop-to-EBP
<span id="L82" class="LineNr">82 </span> c3/return
<span id="L83" class="LineNr">83 </span>
<span id="L84" class="LineNr">84 </span><span class="subxS2Comment"># . . vim:nowrap:textwidth=0</span>
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