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<a href='https://github.com/akkartik/mu/blob/main/linux/104new-segment.subx'>https://github.com/akkartik/mu/blob/main/linux/104new-segment.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Create a new segment (pool of memory for allocating chunks from) in the form</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment"># of an *allocation descriptor* that can be passed to the memory allocator</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment"># (defined in a later layer).</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment">#</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># Currently an allocation descriptor consists of just the bounds of the pool of</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># available memory:</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment">#</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># curr: address</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment"># end: address</span>
<span id="L10" class="LineNr">10 </span><span class="subxComment">#</span>
<span id="L11" class="LineNr">11 </span><span class="subxComment"># This isn't enough information to reclaim individual allocations. We can't</span>
<span id="L12" class="LineNr">12 </span><span class="subxComment"># support arbitrary reclamation yet.</span>
<span id="L13" class="LineNr">13 </span>
<span id="L14" class="LineNr">14 </span>== code
<span id="L15" class="LineNr">15 </span><span class="subxComment"># instruction effective address register displacement immediate</span>
<span id="L16" class="LineNr">16 </span><span class="subxS1Comment"># . op subop mod rm32 base index scale r32</span>
<span id="L17" class="LineNr">17 </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="L18" class="LineNr">18 </span>
<span id="L19" class="LineNr">19 </span><span class="SpecialChar">Entry</span>: <span class="subxComment"># manual test</span>
<span id="L20" class="LineNr">20 </span> <span class="subxComment"># var ad/ecx: allocation-descriptor</span>
<span id="L21" class="LineNr">21 </span> 68/push 0/imm32/limit
<span id="L22" class="LineNr">22 </span> 68/push 0/imm32/curr
<span id="L23" class="LineNr">23 </span> 89/copy 3/mod/direct 1/rm32/ecx <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 ecx</span>
<span id="L24" class="LineNr">24 </span> <span class="subxComment"># new-segment(0x1000, ad)</span>
<span id="L25" class="LineNr">25 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L26" class="LineNr">26 </span> 51/push-ecx
<span id="L27" class="LineNr">27 </span> 68/push 0x1000/imm32
<span id="L28" class="LineNr">28 </span> <span class="subxS2Comment"># . . call</span>
<span id="L29" class="LineNr">29 </span> e8/call <a href='104new-segment.subx.html#L40'>new-segment</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> 8/imm32 <span class="subxComment"># add to esp</span>
<span id="L32" class="LineNr">32 </span> <span class="subxComment"># var eax: (addr _) = ad->curr</span>
<span id="L33" class="LineNr">33 </span> 8b/copy 0/mod/indirect 1/rm32/ecx <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 *ecx to eax</span>
<span id="L34" class="LineNr">34 </span> <span class="subxComment"># write to *eax to check that we have access to the newly-allocated segment</span>
<span id="L35" class="LineNr">35 </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>
<span id="L36" class="LineNr">36 </span> <span class="subxComment"># syscall(exit, eax)</span>
<span id="L37" class="LineNr">37 </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="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="subxFunction">new-segment</span>: <span class="subxComment"># len: int, ad: (addr allocation-descriptor)</span>
<span id="L41" class="LineNr">41 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L42" class="LineNr">42 </span> 55/push-ebp
<span id="L43" class="LineNr">43 </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="L44" class="LineNr">44 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L45" class="LineNr">45 </span> 50/push-eax
<span id="L46" class="LineNr">46 </span> 53/push-ebx
<span id="L47" class="LineNr">47 </span> <span class="subxComment"># copy len to _mmap-new-segment->len</span>
<span id="L48" class="LineNr">48 </span> 8b/copy 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 0/r32/eax 8/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy *(ebp+8) to eax</span>
<span id="L49" class="LineNr">49 </span> 89/copy 0/mod/indirect 5/rm32/.disp32 <span class="Normal"> . </span> <span class="Normal"> . </span> 0/r32/eax $_mmap-new-segment:len/disp32 <span class="subxComment"># copy eax to *$_mmap-new-segment:len</span>
<span id="L50" class="LineNr">50 </span> <span class="subxComment"># mmap(_mmap-new-segment)</span>
<span id="L51" class="LineNr">51 </span> bb/copy-to-ebx <a href='104new-segment.subx.html#L73'>_mmap-new-segment</a>/imm32
<span id="L52" class="LineNr">52 </span> e8/call <a href='000init.subx.html#L71'>syscall_mmap</a>/disp32
<span id="L53" class="LineNr">53 </span> <span class="subxComment"># copy {eax, eax+len} to *ad</span>
<span id="L54" class="LineNr">54 </span> <span class="subxS1Comment"># . ebx = ad</span>
<span id="L55" class="LineNr">55 </span> 8b/copy 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 3/r32/ebx 0xc/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy *(ebp+12) to ebx</span>
<span id="L56" class="LineNr">56 </span> <span class="subxS1Comment"># . ad->curr = eax</span>
<span id="L57" class="LineNr">57 </span> 89/copy 0/mod/indirect 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="L58" class="LineNr">58 </span> <span class="subxS1Comment"># . ad->end = eax+len</span>
<span id="L59" class="LineNr">59 </span> 03/add 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 0/r32/eax 8/disp8 <span class="Normal"> . </span> <span class="subxComment"># add *(ebp+8) to eax</span>
<span id="L60" class="LineNr">60 </span> 89/copy 1/mod/*+disp8 3/rm32/ebx <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 0/r32/eax 4/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy eax to *(ebx+4)</span>
<span id="L61" class="LineNr">61 </span><span class="Constant">$new-segment:end</span>:
<span id="L62" class="LineNr">62 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L63" class="LineNr">63 </span> 5b/pop-to-ebx
<span id="L64" class="LineNr">64 </span> 58/pop-to-eax
<span id="L65" class="LineNr">65 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L66" class="LineNr">66 </span> 89/copy 3/mod/direct 4/rm32/esp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 5/r32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="subxComment"># copy ebp to esp</span>
<span id="L67" class="LineNr">67 </span> 5d/pop-to-ebp
<span id="L68" class="LineNr">68 </span> c3/return
<span id="L69" class="LineNr">69 </span>
<span id="L70" class="LineNr">70 </span>== data
<span id="L71" class="LineNr">71 </span>
<span id="L72" class="LineNr">72 </span><span class="subxComment"># various constants used here were found in the Linux sources (search for file mman-common.h)</span>
<span id="L73" class="LineNr">73 </span><span class="subxMinorFunction">_mmap-new-segment</span>: <span class="subxComment"># mmap_arg_struct</span>
<span id="L74" class="LineNr">74 </span> <span class="subxComment"># addr</span>
<span id="L75" class="LineNr">75 </span> 0/imm32
<span id="L76" class="LineNr">76 </span><span class="Constant">$_mmap-new-segment:len</span>:
<span id="L77" class="LineNr">77 </span> <span class="subxComment"># len</span>
<span id="L78" class="LineNr">78 </span> 0/imm32
<span id="L79" class="LineNr">79 </span> <span class="subxComment"># protection flags</span>
<span id="L80" class="LineNr">80 </span> 3/imm32 <span class="subxComment"># PROT_READ | PROT_WRITE</span>
<span id="L81" class="LineNr">81 </span> <span class="subxComment"># sharing flags</span>
<span id="L82" class="LineNr">82 </span> 0x22/imm32 <span class="subxComment"># MAP_PRIVATE | MAP_ANONYMOUS</span>
<span id="L83" class="LineNr">83 </span> <span class="subxComment"># fd</span>
<span id="L84" class="LineNr">84 </span> -1/imm32 <span class="subxComment"># since MAP_ANONYMOUS is specified</span>
<span id="L85" class="LineNr">85 </span> <span class="subxComment"># offset</span>
<span id="L86" class="LineNr">86 </span> 0/imm32 <span class="subxComment"># since MAP_ANONYMOUS is specified</span>
<span id="L87" class="LineNr">87 </span>
<span id="L88" class="LineNr">88 </span><span class="subxS2Comment"># . . vim:nowrap:textwidth=0</span>
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