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<a href='https://github.com/akkartik/mu/blob/main/linux/313index-bounds-check.subx'>https://github.com/akkartik/mu/blob/main/linux/313index-bounds-check.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Helper to check an array's bounds, and to abort if they're violated.</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment"># Really only intended to be called from code generated by mu.subx.</span>
<span id="L3" class="LineNr"> 3 </span>
<span id="L4" class="LineNr"> 4 </span>== code
<span id="L5" class="LineNr"> 5 </span>
<span id="L6" class="LineNr"> 6 </span><span class="subxMinorFunction">__check-mu-array-bounds</span>: <span class="subxComment"># index: int, elem-size: int, arr-size: int, function-name: (addr array byte), array-name: (addr array byte)</span>
<span id="L7" class="LineNr"> 7 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L8" class="LineNr"> 8 </span> 55/push-ebp
<span id="L9" class="LineNr"> 9 </span> 89/<- %ebp 4/r32/esp
<span id="L10" class="LineNr"> 10 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L11" class="LineNr"> 11 </span> 50/push-eax
<span id="L12" class="LineNr"> 12 </span> 51/push-ecx
<span id="L13" class="LineNr"> 13 </span> 52/push-edx
<span id="L14" class="LineNr"> 14 </span> <span class="subxS1Comment"># . not bothering saving ebx; it's only clobbered if we're going to abort</span>
<span id="L15" class="LineNr"> 15 </span> <span class="subxComment"># ecx = arr-size</span>
<span id="L16" class="LineNr"> 16 </span> 8b/-> *(ebp+0x10) 1/r32/ecx
<span id="L17" class="LineNr"> 17 </span> <span class="subxComment"># var overflow/edx: int = 0</span>
<span id="L18" class="LineNr"> 18 </span> ba/copy-to-edx 0/imm32
<span id="L19" class="LineNr"> 19 </span> <span class="subxComment"># var offset/eax: int = index * elem-size</span>
<span id="L20" class="LineNr"> 20 </span> 8b/-> *(ebp+8) 0/r32/eax
<span id="L21" class="LineNr"> 21 </span> f7 4/subop/multiply-eax-with *(ebp+0xc)
<span id="L22" class="LineNr"> 22 </span> <span class="subxComment"># check for overflow</span>
<span id="L23" class="LineNr"> 23 </span> 81 7/subop/compare %edx 0/imm32
<span id="L24" class="LineNr"> 24 </span> 0f 85/jump-if-!= <a href='313index-bounds-check.subx.html#L6'>__check-mu-array-bounds</a>:overflow/disp32
<span id="L25" class="LineNr"> 25 </span> <span class="subxComment"># check bounds</span>
<span id="L26" class="LineNr"> 26 </span> 39/compare %eax 1/r32/ecx
<span id="L27" class="LineNr"> 27 </span> 0f 82/jump-if-unsigned< $__check-mu-array-bounds:end/disp32 <span class="subxComment"># negative index should always abort</span>
<span id="L28" class="LineNr"> 28 </span> <span class="subxComment"># abort if necessary</span>
<span id="L29" class="LineNr"> 29 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> <span class="Constant">"fn "</span>)
<span id="L30" class="LineNr"> 30 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> *(ebp+0x14))
<span id="L31" class="LineNr"> 31 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> <span class="Constant">": offset "</span>)
<span id="L32" class="LineNr"> 32 </span> (<a href='117write-int-hex.subx.html#L288'>write-int32-hex-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> %eax)
<span id="L33" class="LineNr"> 33 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> <span class="Constant">" is too large for array '"</span>)
<span id="L34" class="LineNr"> 34 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> *(ebp+0x18))
<span id="L35" class="LineNr"> 35 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> <span class="Constant">"'\n"</span>)
<span id="L36" class="LineNr"> 36 </span> (<a href='115write-byte.subx.html#L81'>flush</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span>)
<span id="L37" class="LineNr"> 37 </span> <span class="subxComment"># exit(1)</span>
<span id="L38" class="LineNr"> 38 </span> bb/copy-to-ebx 1/imm32
<span id="L39" class="LineNr"> 39 </span> e8/call <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L40" class="LineNr"> 40 </span> <span class="subxComment"># never gets here</span>
<span id="L41" class="LineNr"> 41 </span><span class="Constant">$__check-mu-array-bounds:end</span>:
<span id="L42" class="LineNr"> 42 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L43" class="LineNr"> 43 </span> 5a/pop-to-edx
<span id="L44" class="LineNr"> 44 </span> 59/pop-to-ecx
<span id="L45" class="LineNr"> 45 </span> 58/pop-to-eax
<span id="L46" class="LineNr"> 46 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L47" class="LineNr"> 47 </span> 89/<- %esp 5/r32/ebp
<span id="L48" class="LineNr"> 48 </span> 5d/pop-to-ebp
<span id="L49" class="LineNr"> 49 </span> c3/return
<span id="L50" class="LineNr"> 50 </span>
<span id="L51" class="LineNr"> 51 </span><span class="subxMinorFunction">__check-mu-array-bounds:overflow</span>:
<span id="L52" class="LineNr"> 52 </span> <span class="subxComment"># "fn " function-name ": offset to array '" array-name "' overflowed 32 bits\n"</span>
<span id="L53" class="LineNr"> 53 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> <span class="Constant">"fn "</span>)
<span id="L54" class="LineNr"> 54 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> *(ebp+0x14))
<span id="L55" class="LineNr"> 55 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> <span class="Constant">": offset to array '"</span>)
<span id="L56" class="LineNr"> 56 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> *(ebp+0x18))
<span id="L57" class="LineNr"> 57 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> <span class="Constant">"' overflowed 32 bits\n"</span>)
<span id="L58" class="LineNr"> 58 </span> (<a href='115write-byte.subx.html#L81'>flush</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span>)
<span id="L59" class="LineNr"> 59 </span> <span class="subxComment"># exit(1)</span>
<span id="L60" class="LineNr"> 60 </span> bb/copy-to-ebx 1/imm32
<span id="L61" class="LineNr"> 61 </span> e8/call <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L62" class="LineNr"> 62 </span> <span class="subxComment"># never gets here</span>
<span id="L63" class="LineNr"> 63 </span>
<span id="L64" class="LineNr"> 64 </span><span class="subxComment"># potential alternative</span>
<span id="L65" class="LineNr"> 65 </span>
<span id="L66" class="LineNr"> 66 </span><span class="CommentedCode">#? __bounds-check: # msg: (addr array byte)</span>
<span id="L67" class="LineNr"> 67 </span><span class="CommentedCode">#? (write-buffered Stderr "abort: array bounds exceeded in fn ")</span>
<span id="L68" class="LineNr"> 68 </span><span class="CommentedCode">#? 8b/-> *(esp+4) 0/r32/eax # we're going to abort, so just clobber away</span>
<span id="L69" class="LineNr"> 69 </span><span class="CommentedCode">#? (write-buffered Stderr %eax)</span>
<span id="L70" class="LineNr"> 70 </span><span class="CommentedCode">#? (write-buffered Stderr Newline)</span>
<span id="L71" class="LineNr"> 71 </span><span class="CommentedCode">#? # exit(1)</span>
<span id="L72" class="LineNr"> 72 </span><span class="CommentedCode">#? bb/copy-to-ebx 1/imm32</span>
<span id="L73" class="LineNr"> 73 </span><span class="CommentedCode">#? e8/call syscall_exit/disp32</span>
<span id="L74" class="LineNr"> 74 </span>
<span id="L75" class="LineNr"> 75 </span><span class="subxComment"># to be called as follows:</span>
<span id="L76" class="LineNr"> 76 </span><span class="subxComment"># var/reg <- index arr/rega: (addr array T), idx/regi: int</span>
<span id="L77" class="LineNr"> 77 </span><span class="subxComment"># | if size-of(T) is 1, 2, 4 or 8</span>
<span id="L78" class="LineNr"> 78 </span><span class="subxComment"># => # temporarily save array size to reg to check bounds</span>
<span id="L79" class="LineNr"> 79 </span><span class="subxComment"># "8b/-> *" rega " " reg "/r32"</span>
<span id="L80" class="LineNr"> 80 </span><span class="subxComment"># "c1/shift 5/subop/right %" reg " " log2(size-of(T)) "/imm32"</span>
<span id="L81" class="LineNr"> 81 </span><span class="subxComment"># "3b/compare " reg "/r32 *" rega</span>
<span id="L82" class="LineNr"> 82 </span><span class="subxComment"># "68/push \"" function "\"/imm32" # pass function name to error message</span>
<span id="L83" class="LineNr"> 83 </span><span class="subxComment"># "0f 8d/jump-if->= __bounds_check/disp32"</span>
<span id="L84" class="LineNr"> 84 </span><span class="subxComment"># "81 0/subop/add %esp 4/imm32" # drop function name</span>
<span id="L85" class="LineNr"> 85 </span><span class="subxComment"># # actually save the index addr in reg</span>
<span id="L86" class="LineNr"> 86 </span><span class="subxComment"># "8d/copy-address *(" rega "+" regi "<<" log2(size-of(T)) "+4) " reg "/r32"</span>
<span id="L87" class="LineNr"> 87 </span>
<span id="L88" class="LineNr"> 88 </span><span class="subxMinorFunction">__mu-abort-null-index-base-address</span>:
<span id="L89" class="LineNr"> 89 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> <span class="Constant">"null address in 'index'\n"</span>)
<span id="L90" class="LineNr"> 90 </span> (<a href='115write-byte.subx.html#L81'>flush</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span>)
<span id="L91" class="LineNr"> 91 </span> <span class="subxComment"># exit(1)</span>
<span id="L92" class="LineNr"> 92 </span> bb/copy-to-ebx 1/imm32
<span id="L93" class="LineNr"> 93 </span> e8/call <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L94" class="LineNr"> 94 </span> <span class="subxComment"># never gets here</span>
<span id="L95" class="LineNr"> 95 </span>
<span id="L96" class="LineNr"> 96 </span><span class="subxMinorFunction">__mu-abort-null-get-base-address</span>:
<span id="L97" class="LineNr"> 97 </span> (<a href='116write-buffered.subx.html#L8'>write-buffered</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span> <span class="Constant">"null address in 'get'\n"</span>)
<span id="L98" class="LineNr"> 98 </span> (<a href='115write-byte.subx.html#L81'>flush</a> <span class="SpecialChar"><a href='116write-buffered.subx.html#L209'>Stderr</a></span>)
<span id="L99" class="LineNr"> 99 </span> <span class="subxComment"># exit(1)</span>
<span id="L100" class="LineNr">100 </span> bb/copy-to-ebx 1/imm32
<span id="L101" class="LineNr">101 </span> e8/call <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L102" class="LineNr">102 </span> <span class="subxComment"># never gets here</span>
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