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<title>Mu - linux/ex8.subx</title>
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<a href='https://github.com/akkartik/mu/blob/main/linux/ex8.subx'>https://github.com/akkartik/mu/blob/main/linux/ex8.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Example reading commandline arguments: compute length of first arg.</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment">#</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment"># To run:</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment">#   $ bootstrap/bootstrap translate ex8.subx -o ex8</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment">#   $ bootstrap/bootstrap run ex8 abc de fghi</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># Expected result:</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment">#   $ echo $?</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment">#   3  # length of 'abc'</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment">#</span>
<span id="L10" class="LineNr">10 </span><span class="subxComment"># At the start of a SubX program:</span>
<span id="L11" class="LineNr">11 </span><span class="subxComment">#   argc: *esp</span>
<span id="L12" class="LineNr">12 </span><span class="subxComment">#   argv[0]: *(esp+4)</span>
<span id="L13" class="LineNr">13 </span><span class="subxComment">#   argv[1]: *(esp+8)</span>
<span id="L14" class="LineNr">14 </span><span class="subxComment">#   ...</span>
<span id="L15" class="LineNr">15 </span><span class="subxComment"># Locals start from esp-4 downwards.</span>
<span id="L16" class="LineNr">16 </span>
<span id="L17" class="LineNr">17 </span>== code
<span id="L18" class="LineNr">18 </span><span class="subxComment">#   instruction                     effective address                                                   register    displacement    immediate</span>
<span id="L19" class="LineNr">19 </span><span class="subxS1Comment"># . op          subop               mod             rm32          base        index         scale       r32</span>
<span id="L20" class="LineNr">20 </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="L21" class="LineNr">21 </span>
<span id="L22" class="LineNr">22 </span><span class="SpecialChar">Entry</span>:
<span id="L23" class="LineNr">23 </span>    <span class="subxS1Comment"># . prologue</span>
<span id="L24" class="LineNr">24 </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="L25" class="LineNr">25 </span>    <span class="subxComment"># eax = ascii-length(argv[1])</span>
<span id="L26" class="LineNr">26 </span>    <span class="subxS2Comment"># . . push args</span>
<span id="L27" class="LineNr">27 </span>    ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>         <span class="Normal"> . </span>          8/disp8        <span class="Normal"> . </span>                <span class="subxComment"># push *(ebp+8)</span>
<span id="L28" class="LineNr">28 </span>    <span class="subxS2Comment"># . . call</span>
<span id="L29" class="LineNr">29 </span>    e8/call  <a href='ex8.subx.html#L37'>ascii-length</a>/disp32
<span id="L30" class="LineNr">30 </span>    <span class="subxS2Comment"># . . discard args</span>
<span id="L31" class="LineNr">31 </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>              4/imm32           <span class="subxComment"># add to esp</span>
<span id="L32" class="LineNr">32 </span>
<span id="L33" class="LineNr">33 </span>    <span class="subxComment"># exit(eax)</span>
<span id="L34" class="LineNr">34 </span>    89/copy                         3/mod/direct    3/rm32/ebx   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          0/r32/eax  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy eax to ebx</span>
<span id="L35" class="LineNr">35 </span>    e8/call  <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L36" class="LineNr">36 </span>
<span id="L37" class="LineNr">37 </span><span class="subxFunction">ascii-length</span>:  <span class="subxComment"># s: (addr array byte) -&gt; n/eax</span>
<span id="L38" class="LineNr">38 </span>    <span class="subxComment"># edx = s</span>
<span id="L39" class="LineNr">39 </span>    8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/esp  4/index/none <span class="Normal"> . </span>          2/r32/edx   4/disp8        <span class="Normal"> . </span>                <span class="subxComment"># copy *(esp+4) to edx</span>
<span id="L40" class="LineNr">40 </span>    <span class="subxComment"># var result/eax = 0</span>
<span id="L41" class="LineNr">41 </span>    b8/copy-to-eax  0/imm32
<span id="L42" class="LineNr">42 </span><span class="Constant">$ascii-length:loop</span>:
<span id="L43" class="LineNr">43 </span>    <span class="subxComment"># var c/ecx = *s</span>
<span id="L44" class="LineNr">44 </span>    8a/copy-byte                    0/mod/*         2/rm32/edx   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          1/r32/CL   <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy byte at *edx to CL</span>
<span id="L45" class="LineNr">45 </span>    <span class="subxComment"># if (c == '\0') break</span>
<span id="L46" class="LineNr">46 </span>    81          7/subop/compare     3/mod/direct    1/rm32/ecx   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>         <span class="Normal"> . </span>         <span class="Normal"> . </span>              0/imm32/null      <span class="subxComment"># compare ecx</span>
<span id="L47" class="LineNr">47 </span>    74/jump-if-=  $ascii-length:end/disp8
<span id="L48" class="LineNr">48 </span>    <span class="subxComment"># ++s</span>
<span id="L49" class="LineNr">49 </span>    42/increment-edx
<span id="L50" class="LineNr">50 </span>    <span class="subxComment"># ++result</span>
<span id="L51" class="LineNr">51 </span>    40/increment-eax
<span id="L52" class="LineNr">52 </span>    <span class="subxComment"># loop</span>
<span id="L53" class="LineNr">53 </span>    eb/jump  $ascii-length:<span class="Constant">loop</span>/disp8
<span id="L54" class="LineNr">54 </span><span class="Constant">$ascii-length:end</span>:
<span id="L55" class="LineNr">55 </span>    <span class="subxComment"># return eax</span>
<span id="L56" class="LineNr">56 </span>    c3/return
<span id="L57" class="LineNr">57 </span>
<span id="L58" class="LineNr">58 </span>== data
<span id="L59" class="LineNr">59 </span>
<span id="L60" class="LineNr">60 </span><span class="subxS2Comment"># . . vim&#0058;nowrap:textwidth=0</span>
</pre>
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