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<a href='https://github.com/akkartik/mu/blob/main/linux/108write.subx'>https://github.com/akkartik/mu/blob/main/linux/108write.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># write: like _write, but also support in-memory streams in addition to file</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment"># descriptors.</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment">#</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># Our first dependency-injected and testable primitive. We can pass it either</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># a file descriptor or an address to a stream. If a file descriptor is passed</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># in, we _write to it using the right syscall. If a 'fake file descriptor' or</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment"># stream is passed in, we append to the stream. This lets us redirect output</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># in tests and check it later.</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment">#</span>
<span id="L10" class="LineNr"> 10 </span><span class="subxComment"># We assume our data segment will never begin at an address shorter than</span>
<span id="L11" class="LineNr"> 11 </span><span class="subxComment"># 0x08000000, so any smaller arguments are assumed to be real file descriptors.</span>
<span id="L12" class="LineNr"> 12 </span><span class="subxComment">#</span>
<span id="L13" class="LineNr"> 13 </span><span class="subxComment"># A stream looks like this:</span>
<span id="L14" class="LineNr"> 14 </span><span class="subxComment"># read: int # index at which to read next</span>
<span id="L15" class="LineNr"> 15 </span><span class="subxComment"># write: int # index at which writes go</span>
<span id="L16" class="LineNr"> 16 </span><span class="subxComment"># data: (array byte) # prefixed by size as usual</span>
<span id="L17" class="LineNr"> 17 </span>
<span id="L18" class="LineNr"> 18 </span>== code
<span id="L19" class="LineNr"> 19 </span><span class="subxComment"># instruction effective address register displacement immediate</span>
<span id="L20" class="LineNr"> 20 </span><span class="subxS1Comment"># . op subop mod rm32 base index scale r32</span>
<span id="L21" class="LineNr"> 21 </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="L22" class="LineNr"> 22 </span>
<span id="L23" class="LineNr"> 23 </span><span class="subxComment"># TODO: come up with a way to signal when a write to disk fails</span>
<span id="L24" class="LineNr"> 24 </span><span class="subxFunction">write</span>: <span class="subxComment"># f: fd or (addr stream byte), s: (addr array byte)</span>
<span id="L25" class="LineNr"> 25 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L26" class="LineNr"> 26 </span> 55/push-ebp
<span id="L27" class="LineNr"> 27 </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="L28" class="LineNr"> 28 </span> <span class="subxComment"># if (s == 0) return</span>
<span id="L29" class="LineNr"> 29 </span> 81 7/subop/compare 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 0xc/disp8 0/imm32 <span class="subxComment"># compare *(ebp+12)</span>
<span id="L30" class="LineNr"> 30 </span> 74/jump-if-= $write:end/disp8
<span id="L31" class="LineNr"> 31 </span> <span class="subxComment"># if (f < 0x08000000) _write(f, s) and return # f can't be a user-mode address, so treat it as a kernel file descriptor</span>
<span id="L32" class="LineNr"> 32 </span> 81 7/subop/compare 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 8/disp8 0x08000000/imm32 <span class="subxComment"># compare *(ebp+8)</span>
<span id="L33" class="LineNr"> 33 </span> 73/jump-if-addr>= $write:fake/disp8
<span id="L34" class="LineNr"> 34 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L35" class="LineNr"> 35 </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="L36" class="LineNr"> 36 </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="L37" class="LineNr"> 37 </span> <span class="subxS2Comment"># . . call</span>
<span id="L38" class="LineNr"> 38 </span> e8/call <a href='101_write.subx.html#L12'>_write</a>/disp32
<span id="L39" class="LineNr"> 39 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L40" class="LineNr"> 40 </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="L41" class="LineNr"> 41 </span> eb/jump $write:end/disp8
<span id="L42" class="LineNr"> 42 </span><span class="Constant">$write:fake</span>:
<span id="L43" class="LineNr"> 43 </span> <span class="subxComment"># otherwise, treat 'f' as a stream to append to</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> 51/push-ecx
<span id="L47" class="LineNr"> 47 </span> 52/push-edx
<span id="L48" class="LineNr"> 48 </span> 53/push-ebx
<span id="L49" class="LineNr"> 49 </span> <span class="subxComment"># ecx = f</span>
<span id="L50" class="LineNr"> 50 </span> 8b/copy 1/mod/*+disp8 5/rm32/ebp <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="L51" class="LineNr"> 51 </span> <span class="subxComment"># edx = f->write</span>
<span id="L52" class="LineNr"> 52 </span> 8b/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 *ecx to edx</span>
<span id="L53" class="LineNr"> 53 </span> <span class="subxComment"># ebx = f->size</span>
<span id="L54" class="LineNr"> 54 </span> 8b/copy 1/mod/*+disp8 1/rm32/ecx <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 *(ecx+8) to ebx</span>
<span id="L55" class="LineNr"> 55 </span> <span class="subxComment"># eax = _append-3(&f->data[f->write], &f->data[f->size], s)</span>
<span id="L56" class="LineNr"> 56 </span> <span class="subxS2Comment"># . . push s</span>
<span id="L57" class="LineNr"> 57 </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="L58" class="LineNr"> 58 </span> <span class="subxS2Comment"># . . push &f->data[f->size]</span>
<span id="L59" class="LineNr"> 59 </span> 8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ecx 3/index/ebx <span class="Normal"> . </span> 3/r32/ebx 0xc/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy ecx+ebx+12 to ebx</span>
<span id="L60" class="LineNr"> 60 </span> 53/push-ebx
<span id="L61" class="LineNr"> 61 </span> <span class="subxS2Comment"># . . push &f->data[f->write]</span>
<span id="L62" class="LineNr"> 62 </span> 8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ecx 2/index/edx <span class="Normal"> . </span> 3/r32/ebx 0xc/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy ecx+edx+12 to ebx</span>
<span id="L63" class="LineNr"> 63 </span> 53/push-ebx
<span id="L64" class="LineNr"> 64 </span> <span class="subxS2Comment"># . . call</span>
<span id="L65" class="LineNr"> 65 </span> e8/call <a href='107trace.subx.html#L860'>_append-3</a>/disp32
<span id="L66" class="LineNr"> 66 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L67" class="LineNr"> 67 </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="L68" class="LineNr"> 68 </span> <span class="subxComment"># f->write += eax</span>
<span id="L69" class="LineNr"> 69 </span> 01/add 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"># add eax to *ecx</span>
<span id="L70" class="LineNr"> 70 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L71" class="LineNr"> 71 </span> 5b/pop-to-ebx
<span id="L72" class="LineNr"> 72 </span> 5a/pop-to-edx
<span id="L73" class="LineNr"> 73 </span> 59/pop-to-ecx
<span id="L74" class="LineNr"> 74 </span> 58/pop-to-eax
<span id="L75" class="LineNr"> 75 </span><span class="Constant">$write:end</span>:
<span id="L76" class="LineNr"> 76 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L77" class="LineNr"> 77 </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="L78" class="LineNr"> 78 </span> 5d/pop-to-ebp
<span id="L79" class="LineNr"> 79 </span> c3/return
<span id="L80" class="LineNr"> 80 </span>
<span id="L81" class="LineNr"> 81 </span><span class="subxTest">test-write-single</span>:
<span id="L82" class="LineNr"> 82 </span> <span class="subxComment"># clear-stream(_test-stream)</span>
<span id="L83" class="LineNr"> 83 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L84" class="LineNr"> 84 </span> 68/push <a href='108write.subx.html#L151'>_test-stream</a>/imm32
<span id="L85" class="LineNr"> 85 </span> <span class="subxS2Comment"># . . call</span>
<span id="L86" class="LineNr"> 86 </span> e8/call <a href='106stream.subx.html#L17'>clear-stream</a>/disp32
<span id="L87" class="LineNr"> 87 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L88" class="LineNr"> 88 </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> 4/imm32 <span class="subxComment"># add to esp</span>
<span id="L89" class="LineNr"> 89 </span> <span class="subxComment"># write(_test-stream, "Ab")</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">"Ab"</span>/imm32
<span id="L92" class="LineNr"> 92 </span> 68/push <a href='108write.subx.html#L151'>_test-stream</a>/imm32
<span id="L93" class="LineNr"> 93 </span> <span class="subxS2Comment"># . . call</span>
<span id="L94" class="LineNr"> 94 </span> e8/call <a href='108write.subx.html#L24'>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="subxComment"># check-ints-equal(*_test-stream->data, 41/A 62/b 00 00, msg)</span>
<span id="L98" class="LineNr"> 98 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L99" class="LineNr"> 99 </span> 68/push <span class="Constant">"F - test-write-single"</span>/imm32
<span id="L100" class="LineNr">100 </span> 68/push 0x006241/imm32/Ab
<span id="L101" class="LineNr">101 </span> <span class="subxS2Comment"># . . push *_test-stream->data</span>
<span id="L102" class="LineNr">102 </span> b8/copy-to-eax <a href='108write.subx.html#L151'>_test-stream</a>/imm32
<span id="L103" class="LineNr">103 </span> ff 6/subop/push 1/mod/*+disp8 0/rm32/eax <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 *(eax+12)</span>
<span id="L104" class="LineNr">104 </span> <span class="subxS2Comment"># . . call</span>
<span id="L105" class="LineNr">105 </span> e8/call <a href='102test.subx.html#L23'>check-ints-equal</a>/disp32
<span id="L106" class="LineNr">106 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L107" class="LineNr">107 </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="L108" class="LineNr">108 </span> <span class="subxComment"># end</span>
<span id="L109" class="LineNr">109 </span> c3/return
<span id="L110" class="LineNr">110 </span>
<span id="L111" class="LineNr">111 </span><span class="subxTest">test-write-appends</span>:
<span id="L112" class="LineNr">112 </span> <span class="subxComment"># clear-stream(_test-stream)</span>
<span id="L113" class="LineNr">113 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L114" class="LineNr">114 </span> 68/push <a href='108write.subx.html#L151'>_test-stream</a>/imm32
<span id="L115" class="LineNr">115 </span> <span class="subxS2Comment"># . . call</span>
<span id="L116" class="LineNr">116 </span> e8/call <a href='106stream.subx.html#L17'>clear-stream</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> 4/imm32 <span class="subxComment"># add to esp</span>
<span id="L119" class="LineNr">119 </span> <span class="subxComment"># write(_test-stream, "C")</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">"C"</span>/imm32
<span id="L122" class="LineNr">122 </span> 68/push <a href='108write.subx.html#L151'>_test-stream</a>/imm32
<span id="L123" class="LineNr">123 </span> <span class="subxS2Comment"># . . call</span>
<span id="L124" class="LineNr">124 </span> e8/call <a href='108write.subx.html#L24'>write</a>/disp32
<span id="L125" class="LineNr">125 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L126" class="LineNr">126 </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="L127" class="LineNr">127 </span> <span class="subxComment"># write(_test-stream, "D")</span>
<span id="L128" class="LineNr">128 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L129" class="LineNr">129 </span> 68/push <span class="Constant">"D"</span>/imm32
<span id="L130" class="LineNr">130 </span> 68/push <a href='108write.subx.html#L151'>_test-stream</a>/imm32
<span id="L131" class="LineNr">131 </span> <span class="subxS2Comment"># . . call</span>
<span id="L132" class="LineNr">132 </span> e8/call <a href='108write.subx.html#L24'>write</a>/disp32
<span id="L133" class="LineNr">133 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L134" class="LineNr">134 </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="L135" class="LineNr">135 </span> <span class="subxComment"># check-ints-equal(*_test-stream->data, 43/C 44/D 00 00, msg)</span>
<span id="L136" class="LineNr">136 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L137" class="LineNr">137 </span> 68/push <span class="Constant">"F - test-write-appends"</span>/imm32
<span id="L138" class="LineNr">138 </span> 68/push 0x00004443/imm32/C-D
<span id="L139" class="LineNr">139 </span> <span class="subxS2Comment"># . . push *_test-stream->data</span>
<span id="L140" class="LineNr">140 </span> b8/copy-to-eax <a href='108write.subx.html#L151'>_test-stream</a>/imm32
<span id="L141" class="LineNr">141 </span> ff 6/subop/push 1/mod/*+disp8 0/rm32/eax <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 *(eax+12)</span>
<span id="L142" class="LineNr">142 </span> <span class="subxS2Comment"># . . call</span>
<span id="L143" class="LineNr">143 </span> e8/call <a href='102test.subx.html#L23'>check-ints-equal</a>/disp32
<span id="L144" class="LineNr">144 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L145" class="LineNr">145 </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="L146" class="LineNr">146 </span> <span class="subxComment"># end</span>
<span id="L147" class="LineNr">147 </span> c3/return
<span id="L148" class="LineNr">148 </span>
<span id="L149" class="LineNr">149 </span>== data
<span id="L150" class="LineNr">150 </span>
<span id="L151" class="LineNr">151 </span><span class="subxMinorFunction">_test-stream</span>: <span class="subxComment"># (stream byte)</span>
<span id="L152" class="LineNr">152 </span> <span class="subxComment"># current write index</span>
<span id="L153" class="LineNr">153 </span> 0/imm32
<span id="L154" class="LineNr">154 </span> <span class="subxComment"># current read index</span>
<span id="L155" class="LineNr">155 </span> 0/imm32
<span id="L156" class="LineNr">156 </span> <span class="subxComment"># size</span>
<span id="L157" class="LineNr">157 </span> 0x10/imm32
<span id="L158" class="LineNr">158 </span> <span class="subxComment"># data (2 lines x 8 bytes/line)</span>
<span id="L159" class="LineNr">159 </span> 00 00 00 00 00 00 00 00
<span id="L160" class="LineNr">160 </span> 00 00 00 00 00 00 00 00
<span id="L161" class="LineNr">161 </span>
<span id="L162" class="LineNr">162 </span><span class="subxS2Comment"># . . vim:nowrap:textwidth=0</span>
</pre>
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