401test.mu - mu - Soul of a tiny new machine. More thorough tests → More comprehensible and rewrite-friendly software → More resilient society.

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# Some helpers for Mu tests.

fn check-true val: boolean, msg: (addr array byte) {
  var tmp/eax: int <- copy val
  check-ints-equal tmp, 1, msg
}

fn check-false val: boolean, msg: (addr array byte) {
  var tmp/eax: int <- copy val
  check-ints-equal tmp, 0, msg
}

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<a href='https://github.com/akkartik/mu/blob/main/linux/101_write.subx'>https://github.com/akkartik/mu/blob/main/linux/101_write.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># _write: write to a file descriptor (fd)</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="SpecialChar">Entry</span>:  <span class="subxComment"># just exit; can't test _write just yet</span>
<span id="L9" class="LineNr"> 9 </span>    bb/copy-to-ebx  0/imm32
<span id="L10" class="LineNr">10 </span>    e8/call  <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L11" class="LineNr">11 </span>
<span id="L12" class="LineNr">12 </span><span class="subxMinorFunction">_write</span>:  <span class="subxComment"># fd: int, s: (addr array byte)</span>
<span id="L13" class="LineNr">13 </span>    <span class="subxS1Comment"># . prologue</span>
<span id="L14" class="LineNr">14 </span>    55/push-ebp
<span id="L15" class="LineNr">15 </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="L16" class="LineNr">16 </span>    <span class="subxS1Comment"># . save registers</span>
<span id="L17" class="LineNr">17 </span>    50/push-eax
<span id="L18" class="LineNr">18 </span>    51/push-ecx
<span id="L19" class="LineNr">19 </span>    52/push-edx
<span id="L20" class="LineNr">20 </span>    53/push-ebx
<span id="L21" class="LineNr">21 </span>    <span class="subxComment"># syscall(write, fd, (data) s+4, (size) *s)</span>
<span id="L22" class="LineNr">22 </span>    <span class="subxS1Comment"># . ebx = fd</span>
<span id="L23" class="LineNr">23 </span>    8b/copy                         1/mod/*+disp8   5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          3/r32/ebx   8/disp8        <span class="Normal"> . </span>                <span class="subxComment"># copy *(ebp+8) to ebx</span>
<span id="L24" class="LineNr">24 </span>    <span class="subxS1Comment"># . var data/ecx: (addr byte) = s+4</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>          1/r32/ecx   0xc/disp8      <span class="Normal"> . </span>                <span class="subxComment"># copy *(ebp+12) to ecx</span>
<span id="L26" class="LineNr">26 </span>    81          0/subop/add         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>              4/imm32           <span class="subxComment"># add to ecx</span>
<span id="L27" class="LineNr">27 </span>    <span class="subxS1Comment"># . var size/edx: int = *s</span>
<span id="L28" class="LineNr">28 </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="L29" class="LineNr">29 </span>    8b/copy                         0/mod/indirect  2/rm32/edx   <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"># copy *edx to edx</span>
<span id="L30" class="LineNr">30 </span>    <span class="subxS1Comment"># . syscall</span>
<span id="L31" class="LineNr">31 </span>    e8/call  <a href='000init.subx.html#L29'>syscall_write</a>/disp32
<span id="L32" class="LineNr">32 </span>    <span class="subxComment"># if (eax &lt; 0) abort</span>
<span id="L33" class="LineNr">33 </span>    3d/compare-eax-with  0/imm32
<span id="L34" class="LineNr">34 </span>    0f 8c/jump-if-&lt;  $_write:abort/disp32
<span id="L35" class="LineNr">35 </span><span class="Constant">$_write:end</span>:
<span id="L36" class="LineNr">36 </span>    <span class="subxS1Comment"># . restore registers</span>
<span id="L37" class="LineNr">37 </span>    5b/pop-to-ebx
<span id="L38" class="LineNr">38 </span>    5a/pop-to-edx
<span id="L39" class="LineNr">39 </span>    59/pop-to-ecx
<span id="L40" class="LineNr">40 </span>    58/pop-to-eax
<span id="L41" class="LineNr">41 </span>    <span class="subxS1Comment"># . epilogue</span>
<span id="L42" class="LineNr">42 </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="L43" class="LineNr">43 </span>    5d/pop-to-ebp
<span id="L44" class="LineNr">44 </span>    c3/return
<span id="L45" class="LineNr">45 </span>
<span id="L46" class="LineNr">46 </span><span class="Constant">$_write:abort</span>:
<span id="L47" class="LineNr">47 </span>    <span class="subxComment"># can't write a message here for risk of an infinite loop, so we'll use a special exit code instead</span>
<span id="L48" class="LineNr">48 </span>    <span class="subxS1Comment"># . syscall(exit, 255)</span>
<span id="L49" class="LineNr">49 </span>    bb/copy-to-ebx  0xff/imm32
<span id="L50" class="LineNr">50 </span>    e8/call  <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L51" class="LineNr">51 </span>    <span class="subxComment"># never gets here</span>
<span id="L52" class="LineNr">52 </span>
<span id="L53" class="LineNr">53 </span><span class="subxS2Comment"># . . vim&#0058;nowrap:textwidth=0</span>
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