144 lines
12 KiB
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144 lines
12 KiB
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<a href='https://github.com/akkartik/mu/blob/master/050_write.subx'>https://github.com/akkartik/mu/blob/master/050_write.subx</a>
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<pre id='vimCodeElement'>
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<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># _write: write to a file descriptor (fd)</span>
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<span id="L2" class="LineNr"> 2 </span>
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<span id="L3" class="LineNr"> 3 </span>== code
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<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># instruction effective address register displacement immediate</span>
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<span id="L5" class="LineNr"> 5 </span><span class="subxS1Comment"># . op subop mod rm32 base index scale r32</span>
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<span id="L6" class="LineNr"> 6 </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="L7" class="LineNr"> 7 </span>
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<span id="L8" class="LineNr"> 8 </span><span class="SpecialChar">Entry</span>: <span class="subxComment"># just exit; can't test _write just yet</span>
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<span id="L9" class="LineNr"> 9 </span> <span class="subxS1Comment"># . syscall(exit, 0)</span>
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<span id="L10" class="LineNr">10 </span> bb/copy-to-ebx 0/imm32
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<span id="L11" class="LineNr">11 </span> b8/copy-to-eax 1/imm32/exit
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<span id="L12" class="LineNr">12 </span> cd/syscall 0x80/imm8
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<span id="L13" class="LineNr">13 </span>
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<span id="L14" class="LineNr">14 </span><span class="subxComment"># Since this is the first file of SubX code, a note about type comments.</span>
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<span id="L15" class="LineNr">15 </span><span class="subxComment"># Eventually we'll build a slightly higher-level safe language atop SubX.</span>
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<span id="L16" class="LineNr">16 </span><span class="subxComment"># Even though we don't have the safe language yet, we'll start thinking in</span>
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<span id="L17" class="LineNr">17 </span><span class="subxComment"># terms of the higher-level types in comments.</span>
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<span id="L18" class="LineNr">18 </span><span class="subxComment">#</span>
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<span id="L19" class="LineNr">19 </span><span class="subxComment"># Mu will have two kinds of addresses:</span>
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<span id="L20" class="LineNr">20 </span><span class="subxComment"># - 'ref' which is used to point to a unique element, because machine</span>
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<span id="L21" class="LineNr">21 </span><span class="subxComment"># code can't store large types in registers.</span>
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<span id="L22" class="LineNr">22 </span><span class="subxComment"># - 'handle' which can point to a heap allocation, different heap allocations</span>
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<span id="L23" class="LineNr">23 </span><span class="subxComment"># at different times, or even at times nothing at all. (Later on handles</span>
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<span id="L24" class="LineNr">24 </span><span class="subxComment"># will turn into fat pointers to enable safe reclamation. But in unsafe</span>
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<span id="L25" class="LineNr">25 </span><span class="subxComment"># levels we'll just never reclaim them, and handles will be word-sized just</span>
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<span id="L26" class="LineNr">26 </span><span class="subxComment"># like refs.)</span>
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<span id="L27" class="LineNr">27 </span><span class="subxComment">#</span>
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<span id="L28" class="LineNr">28 </span><span class="subxComment"># The type 'address' can be obtained from either a ref or handle, but it can</span>
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<span id="L29" class="LineNr">29 </span><span class="subxComment"># only be stored on the stack (say to pass objects by reference).</span>
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<span id="L30" class="LineNr">30 </span><span class="subxComment"># Conversely, a ref can't be copied into another ref, only to an address (which</span>
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<span id="L31" class="LineNr">31 </span><span class="subxComment"># by construction has a shorter lifetime).</span>
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<span id="L32" class="LineNr">32 </span><span class="subxComment">#</span>
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<span id="L33" class="LineNr">33 </span><span class="subxComment"># Beginnings of a lattice of types:</span>
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<span id="L34" class="LineNr">34 </span><span class="subxComment"># You can convert a ref or handle to an address, but not the other way around.</span>
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<span id="L35" class="LineNr">35 </span><span class="subxComment"># You can convert addresses to ints, but not the other way around.</span>
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<span id="L36" class="LineNr">36 </span>
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<span id="L37" class="LineNr">37 </span><span class="subxMinorFunction">_write</span>: <span class="subxComment"># fd : int, s : (addr array byte)</span>
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<span id="L38" class="LineNr">38 </span> <span class="subxS1Comment"># . prologue</span>
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<span id="L39" class="LineNr">39 </span> 55/push-ebp
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<span id="L40" class="LineNr">40 </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>
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<span id="L41" class="LineNr">41 </span> <span class="subxS1Comment"># . save registers</span>
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<span id="L42" class="LineNr">42 </span> 50/push-eax
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<span id="L43" class="LineNr">43 </span> 51/push-ecx
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<span id="L44" class="LineNr">44 </span> 52/push-edx
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<span id="L45" class="LineNr">45 </span> 53/push-ebx
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<span id="L46" class="LineNr">46 </span> <span class="subxComment"># syscall(write, fd, (data) s+4, (size) *s)</span>
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<span id="L47" class="LineNr">47 </span> <span class="subxS1Comment"># . fd : ebx</span>
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<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> 3/r32/ebx 8/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy *(ebp+8) to ebx</span>
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<span id="L49" class="LineNr">49 </span> <span class="subxS1Comment"># . data : ecx = s+4</span>
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<span id="L50" class="LineNr">50 </span> 8b/copy 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"># copy *(ebp+12) to ecx</span>
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<span id="L51" class="LineNr">51 </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> 4/imm32 <span class="subxComment"># add to ecx</span>
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<span id="L52" class="LineNr">52 </span> <span class="subxS1Comment"># . size : edx = *s</span>
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<span id="L53" class="LineNr">53 </span> 8b/copy 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"># copy *(ebp+12) to edx</span>
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<span id="L54" class="LineNr">54 </span> 8b/copy 0/mod/indirect 2/rm32/edx <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 edx</span>
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<span id="L55" class="LineNr">55 </span> <span class="subxS1Comment"># . syscall</span>
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<span id="L56" class="LineNr">56 </span> b8/copy-to-eax 4/imm32/write
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<span id="L57" class="LineNr">57 </span> cd/syscall 0x80/imm8
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<span id="L58" class="LineNr">58 </span> <span class="subxComment"># if (eax < 0) abort</span>
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<span id="L59" class="LineNr">59 </span> 3d/compare-eax-with 0/imm32
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<span id="L60" class="LineNr">60 </span> 0f 8c/jump-if-lesser $_write:abort/disp32
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<span id="L61" class="LineNr">61 </span><span class="Constant">$_write:end</span>:
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<span id="L62" class="LineNr">62 </span> <span class="subxS1Comment"># . restore registers</span>
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<span id="L63" class="LineNr">63 </span> 5b/pop-to-ebx
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<span id="L64" class="LineNr">64 </span> 5a/pop-to-edx
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<span id="L65" class="LineNr">65 </span> 59/pop-to-ecx
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<span id="L66" class="LineNr">66 </span> 58/pop-to-eax
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<span id="L67" class="LineNr">67 </span> <span class="subxS1Comment"># . epilogue</span>
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<span id="L68" class="LineNr">68 </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>
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<span id="L69" class="LineNr">69 </span> 5d/pop-to-ebp
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<span id="L70" class="LineNr">70 </span> c3/return
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<span id="L71" class="LineNr">71 </span>
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<span id="L72" class="LineNr">72 </span><span class="Constant">$_write:abort</span>:
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<span id="L73" class="LineNr">73 </span> <span class="subxComment"># can't write a message here for risk of an infinite loop, so we'll use a special exit code instead</span>
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<span id="L74" class="LineNr">74 </span> <span class="subxS1Comment"># . syscall(exit, 255)</span>
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<span id="L75" class="LineNr">75 </span> bb/copy-to-ebx 0xff/imm32
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<span id="L76" class="LineNr">76 </span> b8/copy-to-eax 1/imm32/exit
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<span id="L77" class="LineNr">77 </span> cd/syscall 0x80/imm8
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<span id="L78" class="LineNr">78 </span> <span class="subxComment"># never gets here</span>
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<span id="L79" class="LineNr">79 </span>
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<span id="L80" class="LineNr">80 </span><span class="subxS2Comment"># . . vim:nowrap:textwidth=0</span>
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</pre>
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