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<p class="MsoNormal"><span style="font-size:11.0pt">Hello,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">There is a problem in StackCounter calculation of maxLocals in combination with custom StackMapTableAttribute covering “dead code”.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Feel free to report it as a bug or let me know and I’ll fill it.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Thank you,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Adam<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="color:black">From:
</span></b><span style="color:black">classfile-api-dev <classfile-api-dev-retn@openjdk.org> on behalf of Rafael Winterhalter <rafael.wth@gmail.com><br>
<b>Date: </b>Monday, 19 August 2024 at 22:23<br>
<b>To: </b>classfile-api-dev <classfile-api-dev@openjdk.org><br>
<b>Subject: </b>StackMapTable format error: bad type array size in method<o:p></o:p></span></p>
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<p class="MsoNormal">Hello,</p>
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<p class="MsoNormal">when testing some of the corner cases within the unit tests of Byte Buddy, I found some further errors when it comes to dead code and using ClassWriter. All those cases work when using ASM. As a reproducer, consider the following:</p>
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<pre style="background:#1E1F22"><span style="color:#BCBEC4"><br> ClassFile classFile = ClassFile.<i>of</i>(ClassFile.StackMapsOption.</span><i><span style="color:#C77DBB">DROP_STACK_MAPS</span></i><span style="color:#BCBEC4">);<br> </span><span style="color:#CF8E6D">byte</span><span style="color:#BCBEC4">[] bytes = classFile.build(ClassDesc.<i>of</i>(</span><span style="color:#6AAB73">"foo.Bar"</span><span style="color:#BCBEC4">), classBuilder -> classBuilder.withMethod(<br> </span><span style="color:#6AAB73">"foo"</span><span style="color:#BCBEC4">,<br> MethodTypeDesc.<i>ofDescriptor</i>(</span><span style="color:#6AAB73">"()J"</span><span style="color:#BCBEC4">),<br> </span><span style="color:#2AACB8">0</span><span style="color:#BCBEC4">,<br> methodBuilder -> {<br> methodBuilder.withCode(codeBuilder -> {<br> codeBuilder.new_(ClassDesc.<i>of</i>(RuntimeException.</span><span style="color:#CF8E6D">class</span><span style="color:#BCBEC4">.getName()));<br> codeBuilder.dup();<br> codeBuilder.invokespecial(ClassDesc.<i>of</i>(RuntimeException.</span><span style="color:#CF8E6D">class</span><span style="color:#BCBEC4">.getName()),<br> </span><span style="color:#6AAB73">"<init>"</span><span style="color:#BCBEC4">,<br> MethodTypeDesc.<i>ofDescriptor</i>(</span><span style="color:#6AAB73">"()V"</span><span style="color:#BCBEC4">));<br> codeBuilder.athrow();<br> Label f2 = codeBuilder.newBoundLabel();<br> codeBuilder.lstore(</span><span style="color:#2AACB8">1</span><span style="color:#BCBEC4">);<br> Label f3 = codeBuilder.newBoundLabel();<br> codeBuilder.lload(</span><span style="color:#2AACB8">1</span><span style="color:#BCBEC4">);<br> codeBuilder.lreturn();<br> codeBuilder.with(StackMapTableAttribute.<i>of</i>(List.<i>of</i>(<br> StackMapFrameInfo.<i>of</i>(f2,<br> List.<i>of</i>(StackMapFrameInfo.ObjectVerificationTypeInfo.<i>of</i>(ClassDesc.<i>of</i>(</span><span style="color:#6AAB73">"foo.Bar"</span><span style="color:#BCBEC4">))),<br> List.<i>of</i>(StackMapFrameInfo.SimpleVerificationTypeInfo.</span><i><span style="color:#C77DBB">ITEM_LONG</span></i><span style="color:#BCBEC4">)),<br> StackMapFrameInfo.<i>of</i>(f3,<br> List.<i>of</i>(StackMapFrameInfo.ObjectVerificationTypeInfo.<i>of</i>(ClassDesc.<i>of</i>(</span><span style="color:#6AAB73">"foo.Bar"</span><span style="color:#BCBEC4">)),<br> StackMapFrameInfo.SimpleVerificationTypeInfo.</span><i><span style="color:#C77DBB">ITEM_LONG</span></i><span style="color:#BCBEC4">),<br> List.<i>of</i>())<br> )));<br> });<br> }));<br> </span><span style="color:#CF8E6D">new </span><span style="color:#BCBEC4">ClassLoader() {<br> </span><span style="color:#B3AE60">@Override<br> </span><span style="color:#CF8E6D">protected </span><span style="color:#BCBEC4">Class<?> </span><span style="color:#56A8F5">findClass</span><span style="color:#BCBEC4">(String name) </span><span style="color:#CF8E6D">throws </span><span style="color:#BCBEC4">ClassNotFoundException {<br> </span><span style="color:#CF8E6D">if </span><span style="color:#BCBEC4">(name.equals(</span><span style="color:#6AAB73">"foo.Bar"</span><span style="color:#BCBEC4">)) {<br> </span><span style="color:#CF8E6D">return </span><span style="color:#BCBEC4">defineClass(name, </span><span style="color:#C77DBB">bytes</span><span style="color:#BCBEC4">, </span><span style="color:#2AACB8">0</span><span style="color:#BCBEC4">, </span><span style="color:#C77DBB">bytes</span><span style="color:#BCBEC4">.</span><span style="color:#C77DBB">length</span><span style="color:#BCBEC4">);<br> } </span><span style="color:#CF8E6D">else </span><span style="color:#BCBEC4">{<br> </span><span style="color:#CF8E6D">return super</span><span style="color:#BCBEC4">.findClass(name);<br> }<br> }<br> }.findClass(</span><span style="color:#6AAB73">"foo.Bar"</span><span style="color:#BCBEC4">).getMethods();<o:p></o:p></span></pre>
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<p class="MsoNormal">It gives a class format error. Java agents sometimes have to process all kinds of strange byte code, so ideally these cases should be supported. Is this a bug in the stack map frame attribute writer?</p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks! Rafael</p>
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