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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Unfortunately jdk.internal.classfile.impl.StackMapGenerator is not exposed in the Classfile API and it is not designed to be called by user.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">The right way to drive stack maps generation is through Classfile.StackMapsOption.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Where the default StackMapsOption.STACK_MAPS_WHEN_REQUIRED option will handle majority of use cases with maximum performance:<o:p></o:p></span></p>
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<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo2"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">transformations of valid classes keeping the original stack maps when the code is unchanged<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo2"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">generation of stack maps for new methods<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo2"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">however it does not fix invalid class files at the input of the transformation<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">StackMapsOption.GENERATE_STACK_MAPS option will force SM generation, for the cases like:<o:p></o:p></span></p>
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<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo2"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">stack maps should be generated even when not mandatory by JVMS<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo2"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">source classes of the transformation are missing stack maps and Classfile API is used to fix it<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">There are several specific aspects of the stack maps generation:<o:p></o:p></span></p>
<ol style="margin-top:0cm" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Non-presence of </span><span style="font-size:11.0pt;font-family:"Arial",sans-serif">StackMapAttribute</span><span style="font-size:11.0pt;font-family:"Arial",sans-serif">
<span lang="EN-US">is a valid state for many methods, so this bare information is not enough to trigger the generator.</span></span><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">StackMapGenerator is internally invoked at the last stage of the code generation, where the bytecode array
is fully constructed. </span><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p></o:p></span></li></ol>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">What specific use case are you trying to solve?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Adam<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">classfile-api-dev <classfile-api-dev-retn@openjdk.org> on behalf of David Lloyd <david.lloyd@redhat.com><br>
<b>Date: </b>Monday, 28 August 2023 18:51<br>
<b>To: </b>classfile-api-dev@openjdk.org <classfile-api-dev@openjdk.org><br>
<b>Subject: </b>Minor issue with stack map generator and generics<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">I've been doing more experimenting with this API and ran across a minor issue. The way the stack map generator API is presently structured, it seems difficult to "get-or-generate".<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">For example, I thought to find the stack map for a method, or otherwise generate it if it did not exist, so my code looked something like this (structured for readability):<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"> MethodModel mm = ....;<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"> Optional<StackMapAttribute> optAttr = mm.findAttribute(Attributes.STACK_MAP_TABLE);<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"> StackMapAttribute sma = optAttr.orElseGet(() -> new StackMapGenerator(...).stackMapTableAttribute());<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">But this fails because `StackMapGenerator.stackMapTableAttribute()` returns an `Attribute<? extends StackMapAttribute>` instead of just `StackMapAttribute`. This method returns
an anonymous subclass of `AdHocAttribute`; could it instead be changed to an inner class which also implements `StackMapAttribute`? I think this might be more correct as well because the type argument of `Attribute` seems like it was intended to be a self-type,
and if so, these direct anonymous subclasses (and there are a few of them) seem to violate that intention.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span class="gmailsignatureprefix"><span style="font-size:11.0pt">--
</span></span><span style="font-size:11.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">- DML • he/him<o:p></o:p></span></p>
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