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<a href='https://github.com/akkartik/mu/blob/master/069allocate.subx'>https://github.com/akkartik/mu/blob/master/069allocate.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Helper to dynamically allocate memory on the heap.</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment">#</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment"># We'd like to be able to write tests for functions that allocate memory,</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># making assertions on the precise addresses used. To achieve this we'll pass</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># in an *allocation descriptor* to allocate from.</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment">#</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment"># Allocation descriptors are also useful outside of tests. Assembly and machine</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># code are of necessity unsafe languages, and one of the most insidious kinds</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment"># of bugs unsafe languages expose us to are dangling pointers to memory that</span>
<span id="L10" class="LineNr"> 10 </span><span class="subxComment"># has been freed and potentially even reused for something totally different.</span>
<span id="L11" class="LineNr"> 11 </span><span class="subxComment"># To reduce the odds of such "use after free" errors, SubX programs tend to not</span>
<span id="L12" class="LineNr"> 12 </span><span class="subxComment"># reclaim and reuse dynamically allocated memory. (Running out of memory is far</span>
<span id="L13" class="LineNr"> 13 </span><span class="subxComment"># easier to debug.) Long-running programs that want to reuse memory are mostly</span>
<span id="L14" class="LineNr"> 14 </span><span class="subxComment"># on their own to be careful. However, they do get one bit of help: they can</span>
<span id="L15" class="LineNr"> 15 </span><span class="subxComment"># carve out chunks of memory and then allocate from them manually using this</span>
<span id="L16" class="LineNr"> 16 </span><span class="subxComment"># very same 'allocate' helper. They just need a new allocation descriptor for</span>
<span id="L17" class="LineNr"> 17 </span><span class="subxComment"># their book-keeping.</span>
<span id="L18" class="LineNr"> 18 </span>
<span id="L19" class="LineNr"> 19 </span>== data
<span id="L20" class="LineNr"> 20 </span>
<span id="L21" class="LineNr"> 21 </span><span class="subxComment"># A default allocation descriptor for programs to use.</span>
<span id="L22" class="LineNr"> 22 </span><span class="SpecialChar">Heap</span>: <span class="subxComment"># allocation-descriptor</span>
<span id="L23" class="LineNr"> 23 </span> <span class="subxComment"># curr</span>
<span id="L24" class="LineNr"> 24 </span> 0/imm32
<span id="L25" class="LineNr"> 25 </span> <span class="subxComment"># limit</span>
<span id="L26" class="LineNr"> 26 </span> 0/imm32
<span id="L27" class="LineNr"> 27 </span>
<span id="L28" class="LineNr"> 28 </span><span class="subxComment"># a reasonable default</span>
<span id="L29" class="LineNr"> 29 </span><span class="SpecialChar">Heap-size</span>: <span class="subxComment"># int</span>
<span id="L30" class="LineNr"> 30 </span> 0x400000/imm32/4MB
<span id="L31" class="LineNr"> 31 </span>
<span id="L32" class="LineNr"> 32 </span>== code
<span id="L33" class="LineNr"> 33 </span><span class="subxComment"># instruction effective address register displacement immediate</span>
<span id="L34" class="LineNr"> 34 </span><span class="subxS1Comment"># . op subop mod rm32 base index scale r32</span>
<span id="L35" class="LineNr"> 35 </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="L36" class="LineNr"> 36 </span>
<span id="L37" class="LineNr"> 37 </span><span class="subxComment"># Let's start initializing the default allocation descriptor.</span>
<span id="L38" class="LineNr"> 38 </span>
<span id="L39" class="LineNr"> 39 </span><span class="SpecialChar">Entry</span>:
<span id="L40" class="LineNr"> 40 </span> <span class="subxComment"># initialize heap</span>
<span id="L41" class="LineNr"> 41 </span> <span class="subxS1Comment"># . Heap = new-segment(Heap-size)</span>
<span id="L42" class="LineNr"> 42 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L43" class="LineNr"> 43 </span> 68/push <span class="SpecialChar"><a href='069allocate.subx.html#L22'>Heap</a></span>/imm32
<span id="L44" class="LineNr"> 44 </span> ff 6/subop/push 0/mod/indirect 5/rm32/.disp32 <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="SpecialChar"><a href='069allocate.subx.html#L29'>Heap-size</a></span>/disp32 <span class="subxComment"># push *Heap-size</span>
<span id="L45" class="LineNr"> 45 </span> <span class="subxS2Comment"># . . call</span>
<span id="L46" class="LineNr"> 46 </span> e8/call <a href='053new-segment.subx.html#L41'>new-segment</a>/disp32
<span id="L47" class="LineNr"> 47 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L48" class="LineNr"> 48 </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="L49" class="LineNr"> 49 </span>
<span id="L50" class="LineNr"> 50 </span> e8/call run-tests/disp32 <span class="subxComment"># 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'.</span>
<span id="L51" class="LineNr"> 51 </span><span class="Constant">$array-equal-main:end</span>:
<span id="L52" class="LineNr"> 52 </span> <span class="subxComment"># syscall(exit, Num-test-failures)</span>
<span id="L53" class="LineNr"> 53 </span> 8b/copy 0/mod/indirect 5/rm32/.disp32 <span class="Normal"> . </span> <span class="Normal"> . </span> 3/r32/ebx <span class="SpecialChar"><a href='051test.subx.html#L90'>Num-test-failures</a></span>/disp32 <span class="subxComment"># copy *Num-test-failures to ebx</span>
<span id="L54" class="LineNr"> 54 </span> b8/copy-to-eax 1/imm32/exit
<span id="L55" class="LineNr"> 55 </span> cd/syscall 0x80/imm8
<span id="L56" class="LineNr"> 56 </span>
<span id="L57" class="LineNr"> 57 </span><span class="subxComment"># Claim the next 'n' bytes of memory starting at ad->curr and update ad->curr.</span>
<span id="L58" class="LineNr"> 58 </span><span class="subxComment"># Abort if there isn't enough memory in 'ad'.</span>
<span id="L59" class="LineNr"> 59 </span><span class="subxFunction">allocate</span>: <span class="subxComment"># ad: (addr allocation-descriptor), n: int -> address-or-null/eax: (addr _)</span>
<span id="L60" class="LineNr"> 60 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L61" class="LineNr"> 61 </span> 55/push-ebp
<span id="L62" class="LineNr"> 62 </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="L63" class="LineNr"> 63 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L64" class="LineNr"> 64 </span> 51/push-ecx
<span id="L65" class="LineNr"> 65 </span> 52/push-edx
<span id="L66" class="LineNr"> 66 </span> <span class="subxComment"># ecx = ad</span>
<span id="L67" class="LineNr"> 67 </span> 8b/copy 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 1/r32/ecx 8/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy *(ebp+8) to ecx</span>
<span id="L68" class="LineNr"> 68 </span> <span class="subxComment"># save ad->curr</span>
<span id="L69" class="LineNr"> 69 </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="L70" class="LineNr"> 70 </span> <span class="subxComment"># check if there's enough space</span>
<span id="L71" class="LineNr"> 71 </span> <span class="subxS1Comment"># . edx = ad->curr + n</span>
<span id="L72" class="LineNr"> 72 </span> 89/copy 3/mod/direct 2/rm32/edx <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 edx</span>
<span id="L73" class="LineNr"> 73 </span> 03/add 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"># add *(ebp+12) to edx</span>
<span id="L74" class="LineNr"> 74 </span> 3b/compare 1/mod/*+disp8 1/rm32/ecx <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 2/r32/edx 4/disp8 <span class="Normal"> . </span> <span class="subxComment"># compare edx with *(ecx+4)</span>
<span id="L75" class="LineNr"> 75 </span> 73/jump-if->=-signed $allocate:abort/disp8
<span id="L76" class="LineNr"> 76 </span><span class="Constant">$allocate:commit</span>:
<span id="L77" class="LineNr"> 77 </span> <span class="subxComment"># update ad->curr</span>
<span id="L78" class="LineNr"> 78 </span> 89/copy 0/mod/indirect 1/rm32/ecx <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 *ecx</span>
<span id="L79" class="LineNr"> 79 </span><span class="Constant">$allocate:end</span>:
<span id="L80" class="LineNr"> 80 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L81" class="LineNr"> 81 </span> 5a/pop-to-edx
<span id="L82" class="LineNr"> 82 </span> 59/pop-to-ecx
<span id="L83" class="LineNr"> 83 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L84" class="LineNr"> 84 </span> 89/copy 3/mod/direct 4/rm32/esp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 5/r32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="subxComment"># copy ebp to esp</span>
<span id="L85" class="LineNr"> 85 </span> 5d/pop-to-ebp
<span id="L86" class="LineNr"> 86 </span> c3/return
<span id="L87" class="LineNr"> 87 </span>
<span id="L88" class="LineNr"> 88 </span><span class="Constant">$allocate:abort</span>:
<span id="L89" class="LineNr"> 89 </span> <span class="subxS1Comment"># . _write(2/stderr, error)</span>
<span id="L90" class="LineNr"> 90 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L91" class="LineNr"> 91 </span> 68/push <span class="Constant">"allocate: failed to allocate\n"</span>/imm32
<span id="L92" class="LineNr"> 92 </span> 68/push 2/imm32/stderr
<span id="L93" class="LineNr"> 93 </span> <span class="subxS2Comment"># . . call</span>
<span id="L94" class="LineNr"> 94 </span> e8/call <a href='050_write.subx.html#L14'>_write</a>/disp32
<span id="L95" class="LineNr"> 95 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L96" class="LineNr"> 96 </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="L97" class="LineNr"> 97 </span> <span class="subxS1Comment"># . syscall(exit, 1)</span>
<span id="L98" class="LineNr"> 98 </span> bb/copy-to-ebx 1/imm32
<span id="L99" class="LineNr"> 99 </span> b8/copy-to-eax 1/imm32/exit
<span id="L100" class="LineNr">100 </span> cd/syscall 0x80/imm8
<span id="L101" class="LineNr">101 </span> <span class="subxComment"># never gets here</span>
<span id="L102" class="LineNr">102 </span>
<span id="L103" class="LineNr">103 </span><span class="subxTest">test-allocate-success</span>:
<span id="L104" class="LineNr">104 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L105" class="LineNr">105 </span> 55/push-ebp
<span id="L106" class="LineNr">106 </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="L107" class="LineNr">107 </span> <span class="subxComment"># var ad/ecx: allocation-descriptor = {11, 15}</span>
<span id="L108" class="LineNr">108 </span> 68/push 0xf/imm32/limit
<span id="L109" class="LineNr">109 </span> 68/push 0xb/imm32/curr
<span id="L110" class="LineNr">110 </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="L111" class="LineNr">111 </span> <span class="subxComment"># var eax: (handle byte) = allocate(ad, 3)</span>
<span id="L112" class="LineNr">112 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L113" class="LineNr">113 </span> 68/push 3/imm32
<span id="L114" class="LineNr">114 </span> 51/push-ecx
<span id="L115" class="LineNr">115 </span> <span class="subxS2Comment"># . . call</span>
<span id="L116" class="LineNr">116 </span> e8/call <a href='069allocate.subx.html#L59'>allocate</a>/disp32
<span id="L117" class="LineNr">117 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L118" class="LineNr">118 </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="L119" class="LineNr">119 </span> <span class="subxComment"># check-ints-equal(eax, 11, msg)</span>
<span id="L120" class="LineNr">120 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L121" class="LineNr">121 </span> 68/push <span class="Constant">"F - <a href='069allocate.subx.html#L103'>test-allocate-success</a>: returns current pointer of allocation descriptor"</span>/imm32
<span id="L122" class="LineNr">122 </span> 68/push 0xb/imm32
<span id="L123" class="LineNr">123 </span> 50/push-eax
<span id="L124" class="LineNr">124 </span> <span class="subxS2Comment"># . . call</span>
<span id="L125" class="LineNr">125 </span> e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32
<span id="L126" class="LineNr">126 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L127" class="LineNr">127 </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> 0xc/imm32 <span class="subxComment"># add to esp</span>
<span id="L128" class="LineNr">128 </span> <span class="subxComment"># check-ints-equal(ad->curr, 14, msg)</span>
<span id="L129" class="LineNr">129 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L130" class="LineNr">130 </span> 68/push <span class="Constant">"F - <a href='069allocate.subx.html#L103'>test-allocate-success</a>: updates allocation descriptor"</span>/imm32
<span id="L131" class="LineNr">131 </span> 68/push 0xe/imm32
<span id="L132" class="LineNr">132 </span> ff 6/subop/push 0/mod/indirect 1/rm32/ecx <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="subxComment"># push *ecx</span>
<span id="L133" class="LineNr">133 </span> <span class="subxS2Comment"># . . call</span>
<span id="L134" class="LineNr">134 </span> e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32
<span id="L135" class="LineNr">135 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L136" class="LineNr">136 </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> 0xc/imm32 <span class="subxComment"># add to esp</span>
<span id="L137" class="LineNr">137 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L138" class="LineNr">138 </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="L139" class="LineNr">139 </span> 5d/pop-to-ebp
<span id="L140" class="LineNr">140 </span> c3/return
<span id="L141" class="LineNr">141 </span>
<span id="L142" class="LineNr">142 </span><span class="subxMinorFunction">_pending-test-allocate-failure</span>:
<span id="L143" class="LineNr">143 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L144" class="LineNr">144 </span> 55/push-ebp
<span id="L145" class="LineNr">145 </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="L146" class="LineNr">146 </span> <span class="subxComment"># var ad/ecx: allocation-descriptor = {11, 15}</span>
<span id="L147" class="LineNr">147 </span> 68/push 0xf/imm32/limit
<span id="L148" class="LineNr">148 </span> 68/push 0xb/imm32/curr
<span id="L149" class="LineNr">149 </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="L150" class="LineNr">150 </span> <span class="subxComment"># var eax: (handle byte) = allocate(ad, 6)</span>
<span id="L151" class="LineNr">151 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L152" class="LineNr">152 </span> 68/push 6/imm32
<span id="L153" class="LineNr">153 </span> 51/push-ecx
<span id="L154" class="LineNr">154 </span> <span class="subxS2Comment"># . . call</span>
<span id="L155" class="LineNr">155 </span> e8/call <a href='069allocate.subx.html#L59'>allocate</a>/disp32
<span id="L156" class="LineNr">156 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L157" class="LineNr">157 </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="L158" class="LineNr">158 </span> <span class="subxComment"># check-ints-equal(eax, 0, msg)</span>
<span id="L159" class="LineNr">159 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L160" class="LineNr">160 </span> 68/push <span class="Constant">"F - test-allocate-failure: returns null"</span>/imm32
<span id="L161" class="LineNr">161 </span> 68/push 0/imm32
<span id="L162" class="LineNr">162 </span> 50/push-eax
<span id="L163" class="LineNr">163 </span> <span class="subxS2Comment"># . . call</span>
<span id="L164" class="LineNr">164 </span> e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32
<span id="L165" class="LineNr">165 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L166" class="LineNr">166 </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> 0xc/imm32 <span class="subxComment"># add to esp</span>
<span id="L167" class="LineNr">167 </span> <span class="subxComment"># no change to ad->curr</span>
<span id="L168" class="LineNr">168 </span> <span class="subxS1Comment"># . check-ints-equal(ad->curr, 11)</span>
<span id="L169" class="LineNr">169 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L170" class="LineNr">170 </span> 68/push <span class="Constant">"F - test-allocate-failure: updates allocation descriptor"</span>/imm32
<span id="L171" class="LineNr">171 </span> 68/push 0xb/imm32
<span id="L172" class="LineNr">172 </span> ff 6/subop/push 0/mod/indirect 1/rm32/ecx <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="subxComment"># push *ecx</span>
<span id="L173" class="LineNr">173 </span> <span class="subxS2Comment"># . . call</span>
<span id="L174" class="LineNr">174 </span> e8/call <a href='051test.subx.html#L24'>check-ints-equal</a>/disp32
<span id="L175" class="LineNr">175 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L176" class="LineNr">176 </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> 0xc/imm32 <span class="subxComment"># add to esp</span>
<span id="L177" class="LineNr">177 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L178" class="LineNr">178 </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="L179" class="LineNr">179 </span> 5d/pop-to-ebp
<span id="L180" class="LineNr">180 </span> c3/return
<span id="L181" class="LineNr">181 </span>
<span id="L182" class="LineNr">182 </span><span class="subxComment"># helper: create a nested allocation descriptor (useful for tests)</span>
<span id="L183" class="LineNr">183 </span><span class="subxFunction">allocate-region</span>: <span class="subxComment"># ad: (addr allocation-descriptor), n: int -> new-ad: (handle allocation-descriptor)</span>
<span id="L184" class="LineNr">184 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L185" class="LineNr">185 </span> 55/push-ebp
<span id="L186" class="LineNr">186 </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="L187" class="LineNr">187 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L188" class="LineNr">188 </span> 51/push-ecx
<span id="L189" class="LineNr">189 </span> <span class="subxComment"># eax = allocate(ad, n)</span>
<span id="L190" class="LineNr">190 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L191" class="LineNr">191 </span> ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 0xc/disp8 <span class="Normal"> . </span> <span class="subxComment"># push *(ebp+12)</span>
<span id="L192" class="LineNr">192 </span> ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 8/disp8 <span class="Normal"> . </span> <span class="subxComment"># push *(ebp+8)</span>
<span id="L193" class="LineNr">193 </span> <span class="subxS2Comment"># . . call</span>
<span id="L194" class="LineNr">194 </span> e8/call <a href='069allocate.subx.html#L59'>allocate</a>/disp32
<span id="L195" class="LineNr">195 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L196" class="LineNr">196 </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="L197" class="LineNr">197 </span> <span class="subxComment"># if (eax == 0) abort</span>
<span id="L198" class="LineNr">198 </span> 3d/compare-eax-and 0/imm32
<span id="L199" class="LineNr">199 </span> 74/jump-if-= $allocate-region:abort/disp8
<span id="L200" class="LineNr">200 </span> <span class="subxComment"># earmark 8 bytes at the start for a new allocation descriptor</span>
<span id="L201" class="LineNr">201 </span> <span class="subxS1Comment"># . *eax = eax + 8</span>
<span id="L202" class="LineNr">202 </span> 89/copy 3/mod/direct 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 eax to ecx</span>
<span id="L203" class="LineNr">203 </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> 8/imm32 <span class="subxComment"># add to ecx</span>
<span id="L204" class="LineNr">204 </span> 89/copy 0/mod/indirect 0/rm32/eax <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 1/r32/ecx <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="subxComment"># copy ecx to *eax</span>
<span id="L205" class="LineNr">205 </span> <span class="subxS1Comment"># . *(eax+4) = eax + n</span>
<span id="L206" class="LineNr">206 </span> 89/copy 3/mod/direct 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 eax to ecx</span>
<span id="L207" class="LineNr">207 </span> 03/add 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"># add *(ebp+12) to ecx</span>
<span id="L208" class="LineNr">208 </span> 89/copy 1/mod/*+disp8 0/rm32/eax <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 1/r32/ecx 4/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy ecx to *(eax+4)</span>
<span id="L209" class="LineNr">209 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L210" class="LineNr">210 </span> 59/pop-to-ecx
<span id="L211" class="LineNr">211 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L212" class="LineNr">212 </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="L213" class="LineNr">213 </span> 5d/pop-to-ebp
<span id="L214" class="LineNr">214 </span> c3/return
<span id="L215" class="LineNr">215 </span>
<span id="L216" class="LineNr">216 </span><span class="subxComment"># We could create a more general '$abort' jump target, but then we'd need to do</span>
<span id="L217" class="LineNr">217 </span><span class="subxComment"># a conditional jump followed by loading the error message and an unconditional</span>
<span id="L218" class="LineNr">218 </span><span class="subxComment"># jump. Or we'd need to unconditionally load the error message before a</span>
<span id="L219" class="LineNr">219 </span><span class="subxComment"># conditional jump, even if it's unused the vast majority of the time. This way</span>
<span id="L220" class="LineNr">220 </span><span class="subxComment"># we bloat a potentially cold segment in RAM so we can abort with a single</span>
<span id="L221" class="LineNr">221 </span><span class="subxComment"># instruction.</span>
<span id="L222" class="LineNr">222 </span><span class="Constant">$allocate-region:abort</span>:
<span id="L223" class="LineNr">223 </span> <span class="subxS1Comment"># . _write(2/stderr, error)</span>
<span id="L224" class="LineNr">224 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L225" class="LineNr">225 </span> 68/push <span class="Constant">"allocate-region: failed to allocate\n"</span>/imm32
<span id="L226" class="LineNr">226 </span> 68/push 2/imm32/stderr
<span id="L227" class="LineNr">227 </span> <span class="subxS2Comment"># . . call</span>
<span id="L228" class="LineNr">228 </span> e8/call <a href='050_write.subx.html#L14'>_write</a>/disp32
<span id="L229" class="LineNr">229 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L230" class="LineNr">230 </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="L231" class="LineNr">231 </span> <span class="subxS1Comment"># . syscall(exit, 1)</span>
<span id="L232" class="LineNr">232 </span> bb/copy-to-ebx 1/imm32
<span id="L233" class="LineNr">233 </span> b8/copy-to-eax 1/imm32/exit
<span id="L234" class="LineNr">234 </span> cd/syscall 0x80/imm8
<span id="L235" class="LineNr">235 </span> <span class="subxComment"># never gets here</span>
<span id="L236" class="LineNr">236 </span>
<span id="L237" class="LineNr">237 </span><span class="subxS2Comment"># . . vim:nowrap:textwidth=0</span>
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