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<a href='https://github.com/akkartik/mu/blob/main/linux/ex5.subx'>https://github.com/akkartik/mu/blob/main/linux/ex5.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Read a character from stdin, save it to a local on the stack, write it to stdout.</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 ex5.subx -o ex5</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># $ bootstrap/bootstrap run ex5</span>
<span id="L6" class="LineNr"> 6 </span>
<span id="L7" class="LineNr"> 7 </span>== code
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># instruction effective address register displacement immediate</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxS1Comment"># . op subop mod rm32 base index scale r32</span>
<span id="L10" class="LineNr">10 </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="L11" class="LineNr">11 </span>
<span id="L12" class="LineNr">12 </span><span class="SpecialChar">Entry</span>:
<span id="L13" class="LineNr">13 </span>
<span id="L14" class="LineNr">14 </span> <span class="subxComment"># allocate x on the stack</span>
<span id="L15" class="LineNr">15 </span> 81 5/subop/subtract 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"># subtract from esp</span>
<span id="L16" class="LineNr">16 </span>
<span id="L17" class="LineNr">17 </span> <span class="subxComment"># read(stdin, x, 1)</span>
<span id="L18" class="LineNr">18 </span> <span class="subxS1Comment"># . fd = 0 (stdin)</span>
<span id="L19" class="LineNr">19 </span> bb/copy-to-ebx 0/imm32
<span id="L20" class="LineNr">20 </span> <span class="subxS1Comment"># . data = x (location to write result to)</span>
<span id="L21" class="LineNr">21 </span> 8d/copy-address 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none 1/r32/ecx 4/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy esp+4 to ecx</span>
<span id="L22" class="LineNr">22 </span> <span class="subxS1Comment"># . size = 1 character</span>
<span id="L23" class="LineNr">23 </span> ba/copy-to-edx 1/imm32
<span id="L24" class="LineNr">24 </span> <span class="subxS1Comment"># . syscall</span>
<span id="L25" class="LineNr">25 </span> e8/call <a href='000init.subx.html#L23'>syscall_read</a>/disp32
<span id="L26" class="LineNr">26 </span>
<span id="L27" class="LineNr">27 </span> <span class="subxComment"># syscall(write, stdout, x, 1)</span>
<span id="L28" class="LineNr">28 </span> <span class="subxS1Comment"># . fd = 1 (stdout)</span>
<span id="L29" class="LineNr">29 </span> bb/copy-to-ebx 1/imm32
<span id="L30" class="LineNr">30 </span> <span class="subxS1Comment"># . data = x (location to read from)</span>
<span id="L31" class="LineNr">31 </span> 8d/copy-address 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none 1/r32/ecx 4/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy esp+4 to ecx</span>
<span id="L32" class="LineNr">32 </span> <span class="subxS1Comment"># . size = 1 character</span>
<span id="L33" class="LineNr">33 </span> ba/copy-to-edx 1/imm32
<span id="L34" class="LineNr">34 </span> <span class="subxS1Comment"># . syscall</span>
<span id="L35" class="LineNr">35 </span> e8/call <a href='000init.subx.html#L29'>syscall_write</a>/disp32
<span id="L36" class="LineNr">36 </span>
<span id="L37" class="LineNr">37 </span> <span class="subxComment"># exit(ebx)</span>
<span id="L38" class="LineNr">38 </span> e8/call <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L39" class="LineNr">39 </span>
<span id="L40" class="LineNr">40 </span><span class="subxS2Comment"># . . vim:nowrap:textwidth=0</span>
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