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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) -> 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:nowrap:textwidth=0</span>
</pre>
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