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<p class="MsoNormal"><span style="font-size:11.0pt">Hi Rafael,<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">Code-level attributes are decomposed to code elements, streamed/transformed as pseudo-instructions together with the bytecode instructions and composed back to the relevant attributes by Class-File API. To
insert a new line number, you can call CodeBuilder::lineNumber at required position of code building or transformation. This is the way covering 99% of use cases.<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">Javap is an example of the “raw” attributes consumers minority.<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">After </span><span style="font-size:11.0pt">JDK-8341274 you will be able to receive a Label for a valid bytecode offset in your CustomAttribute mapper. Each Label position is identified by relevant LabelTarget
in the CodeModel stream. All targeted labels are resolved to target bytecode offsets automatically for known code elements and attributes. All targeted labels will be also resolvable to the target bytecode offsets in custom attribute mappers after JDK-8341274.<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">Unfortunately, class file transformation is so complex process with many different use cases, aspects, and contradicting priorities that we cannot always provide equal level of support for everything with
shining perfect API symmetry. I think custom code attributes operating with bytecode offsets should be provided with at least basic level of Class-File API support. However I would not expect the same seamless integration as for the JVMS-defined attributes.<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">Adam<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"><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">Rafael Winterhalter <rafael.wth@gmail.com><br>
<b>Date: </b>Monday, 11 November 2024 at 9:42<br>
<b>To: </b>Adam Sotona <adam.sotona@oracle.com><br>
<b>Cc: </b>Chen Liang <chen.l.liang@oracle.com>, classfile-api-dev <classfile-api-dev@openjdk.org><br>
<b>Subject: </b>[External] : Re: Mapping byte code offsets in custom code attributes<o:p></o:p></span></p>
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<p class="MsoNormal">Hei Adam,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I agree that most use cases should be covered by today's API. I already use the former in my bridge implementation to use ASM with the Class File API. When it comes to LineNumberTableAttribute, I do not understand how it can be useful to
resolve the remaining 1%, though. LineNumberInfo is built around a "startPc". Without an opportunity to resolve a BCI for a generated method, I do not understand how I can create a custom line number table attribute using the Class File API. The CodeBuilder
interface does not expose the created CodeAttribute, which would be needed to resolve a label position to the needed BCI that the LineNumberInfo class requires. At a minimum, I would need CodeBuilder to resolve the current byte code index, but in the end this
would only be used to build a custom label mechanism. I argue that this should already be handled by the API. The same goes for reading. I can of course count the size of each encountered instruction and keep a custom mapping of attributed BCIs to invoke a
custom callback whenever a relevant offset is discovered, but this is also what the Label API is used for, and I think the API should handle this mapping.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I find the same limitation with LocalVariableTypeInfo, LocalVariableInfo and CharacterRangeInfo. I also believe this was considered for type annotations where TypeAnnotation.TargetInfo.OffsetTarget resolves a label, and not a BCI. I expected
consistent handling for all attributes other than type annotations, including custom attributes.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Best regards, Rafael<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Am Mo., 11. Nov. 2024 um 09:17 Uhr schrieb Adam Sotona <<a href="mailto:adam.sotona@oracle.com">adam.sotona@oracle.com</a>>:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Hi Rafael,</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">LineNumber, LocalVariable and LocalVariableType (as CodeElements) are integral parts of the Class-File API and they should serve well to 99% of user
use cases.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">In addition, LineNumberTableAttribute, LocalVariableTableAttribute, LocalVariableTypeTableAttribute and StackMapTableAttribute are available in “raw”
forms to support strongly requested specific corner cases.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">This is clear request to support custom code-level attributes with references to bytecode offsets.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">I agree with Chen that JDK-8341274 should be sufficient to resolve it.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Thank you,</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Adam
</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt"><b><span style="color:black">From:
</span></b><span style="color:black">classfile-api-dev <<a href="mailto:classfile-api-dev-retn@openjdk.org" target="_blank">classfile-api-dev-retn@openjdk.org</a>> on behalf of Chen Liang <<a href="mailto:chen.l.liang@oracle.com" target="_blank">chen.l.liang@oracle.com</a>><br>
<b>Date: </b>Monday, 11 November 2024 at 0:28<br>
<b>To: </b>Rafael Winterhalter <<a href="mailto:rafael.wth@gmail.com" target="_blank">rafael.wth@gmail.com</a>>, classfile-api-dev <<a href="mailto:classfile-api-dev@openjdk.org" target="_blank">classfile-api-dev@openjdk.org</a>><br>
<b>Subject: </b>Re: Mapping byte code offsets in custom code attributes</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black">Hi Rafael,</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black">You are correct. I had previously created an issue
<a href="https://bugs.openjdk.org/browse/JDK-8341274" target="_blank">https://bugs.openjdk.org/browse/JDK-8341274</a> to track this demand. Since this scenario has no way to bypass, maybe we can raise this issue to P3 and work on this feature for JDK 24.
Also I wonder how frequently are custom attributes storing BCIs?</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black">For LineNumberInfo: I believe the Label-based version, LineNumber, is already streamed in class file reading, and can be sent to the builder also via CodeBuilder::lineNumber(int).
Your particular use case can probably be covered by the RFE too, once we can convert labels to BCIs in non-Code attributes.</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black">Regards,</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black">Chen Liang</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:black">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:black"> classfile-api-dev
<<a href="mailto:classfile-api-dev-retn@openjdk.org" target="_blank">classfile-api-dev-retn@openjdk.org</a>> on behalf of Rafael Winterhalter <<a href="mailto:rafael.wth@gmail.com" target="_blank">rafael.wth@gmail.com</a>><br>
<b>Sent:</b> Saturday, November 9, 2024 2:32 AM<br>
<b>To:</b> classfile-api-dev <<a href="mailto:classfile-api-dev@openjdk.org" target="_blank">classfile-api-dev@openjdk.org</a>><br>
<b>Subject:</b> Mapping byte code offsets in custom code attributes</span> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Hello,<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">I mentioned before that I think there is still a missing bit when it comes to custom code attributes, and mapping them using an AttributeMapper. Many code attributes point to a
location, or area, within a method. This typically implies specifying one or two byte code offsets within an attribute.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">To implement this, I would need a possibility to translate offsets to labels within an attribute mapper, and vice versa. For example, if I created byte code from a different source,
where a method consists of multiple files, I would want to mark what part of the method comes from what file.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">I do not currently know of a way to do this in the Class File API. To resolve this, I would have hoped that the attribute reader method would be able to issue labels that are later
issued when the code instructions are supplied. Similarly, I would have hoped that the attribute writer method would be capable of translating labels to byte code offsets.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">In the same way, I would have hoped that all attributes such as LineNumberInfo of the LineNumberTableAttribute would expose bytecode offsets as labels and not as integers, as the
latter does not really give any useful information by itself. This way, I could also write a custom LineNumberTableAttribute after a method is already created by issuing relevant labels, but by only writing the attribute when the entire method was visited.
Sometimes this is necessary when generating code, when the information about the actual line numbers is only retrieved at a later stage that requires knowledge of the entire method.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">As I understand it, the ClassFile API is supposed to be released in Java 24. Are there still plans to integrate such a change? After that it would require incompatible changes,
therefore I had hoped this would make it into the final version.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Thanks! Rafael<o:p></o:p></p>
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