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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I noticed a possible Buffer Overflow issue in one of the auto-generated files by AsmWriterEmitter.cpp
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The snippet of code generated by the emitter is :<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">‘’’’’<o:p></o:p></p>
<p class="MsoNormal"> uint64_t Bits1 = OpInfo[MI->getOpcode()];<o:p></o:p></p>
<p class="MsoNormal"> uint64_t Bits2 = OpInfo2[MI->getOpcode()];<o:p></o:p></p>
<p class="MsoNormal"> uint64_t Bits = (Bits2 << 32) | Bits1;<o:p></o:p></p>
<p class="MsoNormal"> assert(Bits != 0 && "Cannot print this instruction.");<o:p></o:p></p>
<p class="MsoNormal"> O << AsmStrs+(Bits & 4095)-1;<o:p></o:p></p>
<p class="MsoNormal">‘’’’’<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The risk is that Bits1 and Bits2 could read 0x0 for certain opcodes. If this happens, “(Bits & 4095)-1” would evaluate to -1, causing an out of bounds address being put out to raw_ostream O.<o:p></o:p></p>
<p class="MsoNormal">There is an assert to check for this very case, but I am wondering if we need to bail out with an error ( maybe a ‘report_fatal_error’) in addition to an assert?
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The lines in AsmWritterEmitter generating this snippet (line 450 – 461):<o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
<o:p></o:p></span></b></p>
<p class="MsoNormal" style="text-autospace:none">’’’’<o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">if</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">(BitsLeft<b>
</b><<b> </b>32)<b> </b>{<b><o:p></o:p></b></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:green;background:white;mso-highlight:white">// If we have two tables then we need to perform two lookups and combine</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p></o:p></span></b></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:green;background:white;mso-highlight:white">// the results into a single 64-bit value.</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p></o:p></span></b></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:gray;background:white;mso-highlight:white">O</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><<<b>
</b></span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">" uint64_t Bits1 = OpInfo[MI->getOpcode()];\n"</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p></o:p></span></b></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><<<b>
</b></span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">" uint64_t Bits2 = OpInfo2[MI->getOpcode()];\n"</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p></o:p></span></b></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><<<b>
</b></span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">" uint64_t Bits = (Bits2 << 32) | Bits1;\n"</span><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">;<b><o:p></o:p></b></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">}<b>
</b></span><span style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">else</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">{<b><o:p></o:p></b></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:green;background:white;mso-highlight:white">// If only one table is used we just need to perform a single lookup.</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p></o:p></span></b></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:gray;background:white;mso-highlight:white">O</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><<<b>
</b></span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">" uint32_t Bits = OpInfo[MI->getOpcode()];\n"</span><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">;<b><o:p></o:p></b></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">}<b><o:p></o:p></b></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:gray;background:white;mso-highlight:white">O</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><<<b>
</b></span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">" assert(Bits != 0 && \"Cannot print this instruction.\");\n"</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><<<b>
</b></span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">" O << AsmStrs+(Bits & "</span><b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span></b><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><<<b>
</b>(1<b> </b><<<b> </b>AsmStrBits)-1<b> </b><<<b> </b></span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">")-1;\n\n"</span><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">;</span><o:p></o:p></p>
<p class="MsoNormal">’’’’<o:p></o:p></p>
<p class="MsoNormal">Appreciate comments.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Satyajeet<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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