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  56 <a href='https://github.com/akkartik/mu/blob/main/linux/ex12.subx'>https://github.com/akkartik/mu/blob/main/linux/ex12.subx</a>
  57 <pre id='vimCodeElement'>
  58 <span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Example showing mmap syscall.</span>
  59 <span id="L2" class="LineNr"> 2 </span><span class="subxComment"># Create a new segment using mmap, save the address, write to it.</span>
  60 <span id="L3" class="LineNr"> 3 </span><span class="subxComment">#</span>
  61 <span id="L4" class="LineNr"> 4 </span><span class="subxComment"># To run:</span>
  62 <span id="L5" class="LineNr"> 5 </span><span class="subxComment">#   $ bootstrap/bootstrap translate ex12.subx -o ex12</span>
  63 <span id="L6" class="LineNr"> 6 </span><span class="subxComment">#   $ bootstrap/bootstrap run ex12</span>
  64 <span id="L7" class="LineNr"> 7 </span><span class="subxComment"># You shouldn't get a segmentation fault.</span>
  65 <span id="L8" class="LineNr"> 8 </span>
  66 <span id="L9" class="LineNr"> 9 </span>== code
  67 <span id="L10" class="LineNr">10 </span><span class="subxComment">#   instruction                     effective address                                                   register    displacement    immediate</span>
  68 <span id="L11" class="LineNr">11 </span><span class="subxS1Comment"># . op          subop               mod             rm32          base        index         scale       r32</span>
  69 <span id="L12" class="LineNr">12 </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>
  70 <span id="L13" class="LineNr">13 </span>
  71 <span id="L14" class="LineNr">14 </span><span class="SpecialChar">Entry</span>:
  72 <span id="L15" class="LineNr">15 </span>    <span class="subxComment"># mmap(Mmap-new-segment-&gt;len)</span>
  73 <span id="L16" class="LineNr">16 </span>    bb/copy-to-ebx  <span class="SpecialChar"><a href='ex12.subx.html#L29'>Mmap-new-segment</a></span>/imm32
  74 <span id="L17" class="LineNr">17 </span>    e8/call  <a href='000init.subx.html#L71'>syscall_mmap</a>/disp32
  75 <span id="L18" class="LineNr">18 </span>
  76 <span id="L19" class="LineNr">19 </span>    <span class="subxComment"># write to *eax to check that we have access to the newly-allocated segment</span>
  77 <span id="L20" class="LineNr">20 </span>    c7          0/subop/copy        0/mod/direct    0/rm32/eax   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>         <span class="Normal"> . </span>         <span class="Normal"> . </span>              0x34/imm32        <span class="subxComment"># copy to *eax</span>
  78 <span id="L21" class="LineNr">21 </span>
  79 <span id="L22" class="LineNr">22 </span>    <span class="subxComment"># exit(eax)</span>
  80 <span id="L23" class="LineNr">23 </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>
  81 <span id="L24" class="LineNr">24 </span>    e8/call  <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
  82 <span id="L25" class="LineNr">25 </span>
  83 <span id="L26" class="LineNr">26 </span>== data
  84 <span id="L27" class="LineNr">27 </span>
  85 <span id="L28" class="LineNr">28 </span><span class="subxComment"># various constants used here were found in the Linux sources (search for file mman-common.h)</span>
  86 <span id="L29" class="LineNr">29 </span><span class="SpecialChar">Mmap-new-segment</span>:  <span class="subxComment"># type mmap_arg_struct</span>
  87 <span id="L30" class="LineNr">30 </span>    <span class="subxComment"># addr</span>
  88 <span id="L31" class="LineNr">31 </span>    0/imm32
  89 <span id="L32" class="LineNr">32 </span>    <span class="subxComment"># len</span>
  90 <span id="L33" class="LineNr">33 </span>    0x100/imm32
  91 <span id="L34" class="LineNr">34 </span>    <span class="subxComment"># protection flags</span>
  92 <span id="L35" class="LineNr">35 </span>    3/imm32  <span class="subxComment"># PROT_READ | PROT_WRITE</span>
  93 <span id="L36" class="LineNr">36 </span>    <span class="subxComment"># sharing flags</span>
  94 <span id="L37" class="LineNr">37 </span>    0x22/imm32  <span class="subxComment"># MAP_PRIVATE | MAP_ANONYMOUS</span>
  95 <span id="L38" class="LineNr">38 </span>    <span class="subxComment"># fd</span>
  96 <span id="L39" class="LineNr">39 </span>    -1/imm32  <span class="subxComment"># since MAP_ANONYMOUS is specified</span>
  97 <span id="L40" class="LineNr">40 </span>    <span class="subxComment"># offset</span>
  98 <span id="L41" class="LineNr">41 </span>    0/imm32  <span class="subxComment"># since MAP_ANONYMOUS is specified</span>
  99 <span id="L42" class="LineNr">42 </span>
 100 <span id="L43" class="LineNr">43 </span><span class="subxS2Comment"># . . vim&#0058;nowrap:textwidth=0</span>
 101 </pre>
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