105 lines
6.6 KiB
HTML
105 lines
6.6 KiB
HTML
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<a href='https://github.com/akkartik/mu/blob/main/linux/ex12.subx'>https://github.com/akkartik/mu/blob/main/linux/ex12.subx</a>
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<pre id='vimCodeElement'>
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<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Example showing mmap syscall.</span>
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<span id="L2" class="LineNr"> 2 </span><span class="subxComment"># Create a new segment using mmap, save the address, write to it.</span>
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<span id="L3" class="LineNr"> 3 </span><span class="subxComment">#</span>
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<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># To run:</span>
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<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># $ bootstrap/bootstrap translate ex12.subx -o ex12</span>
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<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># $ bootstrap/bootstrap run ex12</span>
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<span id="L7" class="LineNr"> 7 </span><span class="subxComment"># You shouldn't get a segmentation fault.</span>
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<span id="L8" class="LineNr"> 8 </span>
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<span id="L9" class="LineNr"> 9 </span>== code
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<span id="L10" class="LineNr">10 </span><span class="subxComment"># instruction effective address register displacement immediate</span>
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<span id="L11" class="LineNr">11 </span><span class="subxS1Comment"># . op subop mod rm32 base index scale r32</span>
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<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>
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<span id="L13" class="LineNr">13 </span>
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<span id="L14" class="LineNr">14 </span><span class="SpecialChar">Entry</span>:
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<span id="L15" class="LineNr">15 </span> <span class="subxComment"># mmap(Mmap-new-segment->len)</span>
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<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
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<span id="L17" class="LineNr">17 </span> e8/call <a href='000init.subx.html#L71'>syscall_mmap</a>/disp32
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<span id="L18" class="LineNr">18 </span>
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<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>
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<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>
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<span id="L21" class="LineNr">21 </span>
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<span id="L22" class="LineNr">22 </span> <span class="subxComment"># exit(eax)</span>
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<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>
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<span id="L24" class="LineNr">24 </span> e8/call <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
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<span id="L25" class="LineNr">25 </span>
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<span id="L26" class="LineNr">26 </span>== data
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<span id="L27" class="LineNr">27 </span>
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<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>
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<span id="L29" class="LineNr">29 </span><span class="SpecialChar">Mmap-new-segment</span>: <span class="subxComment"># type mmap_arg_struct</span>
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<span id="L30" class="LineNr">30 </span> <span class="subxComment"># addr</span>
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<span id="L31" class="LineNr">31 </span> 0/imm32
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<span id="L32" class="LineNr">32 </span> <span class="subxComment"># len</span>
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<span id="L33" class="LineNr">33 </span> 0x100/imm32
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<span id="L34" class="LineNr">34 </span> <span class="subxComment"># protection flags</span>
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<span id="L35" class="LineNr">35 </span> 3/imm32 <span class="subxComment"># PROT_READ | PROT_WRITE</span>
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<span id="L36" class="LineNr">36 </span> <span class="subxComment"># sharing flags</span>
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<span id="L37" class="LineNr">37 </span> 0x22/imm32 <span class="subxComment"># MAP_PRIVATE | MAP_ANONYMOUS</span>
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<span id="L38" class="LineNr">38 </span> <span class="subxComment"># fd</span>
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<span id="L39" class="LineNr">39 </span> -1/imm32 <span class="subxComment"># since MAP_ANONYMOUS is specified</span>
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<span id="L40" class="LineNr">40 </span> <span class="subxComment"># offset</span>
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<span id="L41" class="LineNr">41 </span> 0/imm32 <span class="subxComment"># since MAP_ANONYMOUS is specified</span>
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<span id="L42" class="LineNr">42 </span>
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<span id="L43" class="LineNr">43 </span><span class="subxS2Comment"># . . vim:nowrap:textwidth=0</span>
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</pre>
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