8357220: Introduce a BSMAttributeEntry struct #25298

jdksjolen · 2025-05-19T07:35:16Z

Hi,

The constant pool currently has a lot of methods specific to extracting parts of the operands array. What this array actually is, is a sequence of bootstrap method attribute entries, where each entry has the following components:

struct BSMAE {
  u2 bootstrap_method_index;
  u2 argument_count;
  u2 arguments[argument_count];
}

We can removes some of these operands array specific methods, and instead allows you to extract BSMAttributeEntrys which you can then use to extract its piece wise components. This makes for a nicer interface, and a bit easier to come into as a reader of the code, as it more closely mirrors the JVMS.

Please consider!

Testing: Currently GHA, running tier1-tier3

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Issue

JDK-8357220: Introduce a BSMAttributeEntry struct (Enhancement - P4)

Reviewers

Coleen Phillimore (@coleenp - Reviewer) Review applies to 1c7484d7
Matias Saavedra Silva (@matias9927 - Reviewer) Review applies to 1c7484d7
Serguei Spitsyn (@sspitsyn - Reviewer)

Contributors

John R Rose <jrose@openjdk.org>

Reviewing

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bridgekeeper · 2025-05-19T07:36:06Z

👋 Welcome back jsjolen! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2025-05-19T07:36:10Z

@jdksjolen This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8357220: Introduce a BSMAttributeEntry struct

Co-authored-by: John R Rose <jrose@openjdk.org>
Reviewed-by: sspitsyn, coleenp, matsaave

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 563 new commits pushed to the master branch:

0dce98b: 8359123: Misleading examples in jmod man page
08b1fa4: 8359972: Problem list TestStaticCallStub until JDK-8359963 is fixed
23e1e2f: 8359180: Apply java.io.Serial annotations in java.instrument
... and 560 more: https://git.openjdk.org/jdk/compare/13b3541467aa91c2e0ad4da70efdb25b7334d3fe...master

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openjdk · 2025-05-19T07:36:41Z

@jdksjolen The following labels will be automatically applied to this pull request:

hotspot
serviceability

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing lists. If you would like to change these labels, use the /label pull request command.

jdksjolen · 2025-05-19T07:36:44Z

/contributor /contributor add @rose00

openjdk · 2025-05-19T07:37:47Z

@jdksjolen Syntax: /contributor (add|remove) [@user | openjdk-user | Full Name <email@address>]. For example:

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jdksjolen · 2025-05-19T07:43:19Z

/contributor add @rose00

openjdk · 2025-05-19T07:43:45Z

@jdksjolen
Contributor John R Rose <jrose@openjdk.org> successfully added.

mlbridge · 2025-05-19T10:08:03Z

Webrevs

plummercj · 2025-05-19T17:49:59Z

src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/oops/ConstantPool.java

+  private static int INDY_BSM_OFFSET = 0;
+  private static int INDY_ARGC_OFFSET = 1;
+  private static int INDY_ARGV_OFFSET = 2;


Is the SA code that references these fields still correct? It seems the references are from the ClassWriter, which we don't have very good test coverage for. Probably this is a bug that is not being detected.

The references are still correct, as we haven't changed the struct layout. We're also not planning on doing so. I don't think that there is a bug here.

Ok. It's just unusual to see constants like these that are needed by SA but serve no purpose in hotspot.

It does seem like you want to mirror these constants from the vmStructs side like it was rather than defining them here in the SA. I see why you did this but maybe you can add the constants to BSMAttributeEntry and declare them constants using declare_constant(BSMAttributeEntry::_indy...).
In case you change them at some later time.

jdksjolen · 2025-05-20T06:33:38Z

src/hotspot/share/oops/constantPool.hpp

-  enum {
-         _indy_bsm_offset  = 0,  // CONSTANT_MethodHandle bsm
-         _indy_argc_offset = 1,  // u2 argc
-         _indy_argv_offset = 2   // u2 argv[argc]
-  };
-


@plummercj , this is where the enum constants come from.

jdksjolen · 2025-05-20T06:34:20Z

src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/oops/ConstantPool.java

+  private static int INDY_BSM_OFFSET = 0;
+  private static int INDY_ARGC_OFFSET = 1;
+  private static int INDY_ARGV_OFFSET = 2;


The references are still correct, as we haven't changed the struct layout. We're also not planning on doing so. I don't think that there is a bug here.

lfoltan

Overall looks good, a couple of comments below.

lfoltan · 2025-05-21T17:28:12Z

src/hotspot/share/oops/constantPool.hpp

  }
 };

+class BSMAttributeEntry {


Please consider moving the description comment from lines #569-#572 ahead of this structure

This?

// The first part of the operands array consists of an index into the second part. // Extract a 32-bit index value from the first part.

Wouldn't it be better to leave it where it is, but add a comment ahead of the structure?

lfoltan · 2025-05-21T17:28:27Z

src/hotspot/share/oops/constantPool.hpp

+  u2* argument_indexes() {
+    return reinterpret_cast<u2*>(this + 1);
+  }
+


Remove blank lines at #92, #95, #103

We typically keep a space before we change access modifier, let's keep that pattern in here. We can tighten up the rest of the code according to your suggestions, however.

lfoltan · 2025-05-21T17:36:03Z

src/hotspot/share/oops/constantPool.hpp

+  }
+
+  int argument_index(int n) const {
+    assert(checked_cast<u2>(n) < _argument_count, "oob");


Should the assert contain a check that _argument_count is >= 0 as well?

I don't think so, it's a u2 so that's just part of its type.

lfoltan · 2025-05-21T17:37:04Z

src/hotspot/share/oops/constantPool.hpp

-               int next_offset = bootstrap_operand_limit(cp_index));
-    assert(end_offset == next_offset, "matched ending");
-    return argc;
+    int bsmai = bootstrap_methods_attribute_index(cp_index);


The "matched ending" assert was the only code that used bootstrap_operand_limit(), so that method could be removed as well. This comment applies to bootstrap_operand_base() as well.

lfoltan · 2025-05-21T17:46:54Z

src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/oops/ConstantPool.java

-  private static int INDY_BSM_OFFSET;
-  private static int INDY_ARGC_OFFSET;
-  private static int INDY_ARGV_OFFSET;
+  private static int INDY_BSM_OFFSET = 0;


Please update the copyright of this file.

jdksjolen

Thank you for the review Lois! I've addressed most of your comments, but I didn't add any documentation for the BSMAttributeEntry (yet).

jdksjolen · 2025-05-22T17:46:15Z

src/hotspot/share/oops/constantPool.hpp

+  u2* argument_indexes() {
+    return reinterpret_cast<u2*>(this + 1);
+  }
+


We typically keep a space before we change access modifier, let's keep that pattern in here. We can tighten up the rest of the code according to your suggestions, however.

jdksjolen · 2025-05-22T17:47:19Z

src/hotspot/share/oops/constantPool.hpp

+  }
+
+  int argument_index(int n) const {
+    assert(checked_cast<u2>(n) < _argument_count, "oob");


I don't think so, it's a u2 so that's just part of its type.

jdksjolen · 2025-05-22T17:47:56Z

src/hotspot/share/oops/constantPool.hpp

-               int next_offset = bootstrap_operand_limit(cp_index));
-    assert(end_offset == next_offset, "matched ending");
-    return argc;
+    int bsmai = bootstrap_methods_attribute_index(cp_index);


jdksjolen · 2025-05-22T17:49:57Z

src/hotspot/share/oops/constantPool.hpp

  }
 };

+class BSMAttributeEntry {


This?

// The first part of the operands array consists of an index into the second part. // Extract a 32-bit index value from the first part.

Wouldn't it be better to leave it where it is, but add a comment ahead of the structure?

coleenp

I think this looks like a nice improvement but I thought operands was going to turn into two arrays? Also there's probably a better name than 'operands' maybe bsm_operands?

coleenp · 2025-05-29T11:38:09Z

src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/oops/ConstantPool.java

+  private static int INDY_BSM_OFFSET = 0;
+  private static int INDY_ARGC_OFFSET = 1;
+  private static int INDY_ARGV_OFFSET = 2;


It does seem like you want to mirror these constants from the vmStructs side like it was rather than defining them here in the SA. I see why you did this but maybe you can add the constants to BSMAttributeEntry and declare them constants using declare_constant(BSMAttributeEntry::_indy...).
In case you change them at some later time.

jdksjolen · 2025-06-09T11:58:12Z

Hi,

I think this looks like a nice improvement but I thought operands was going to turn into two arrays? Also there's probably a better name than 'operands' maybe bsm_operands?

Yeah, I hope to do that in a future PR.

Re: SA mirror constants. OK, I can do that, that makes sense.

coleenp

This looks good. Looking forward to future improvements in this code. Thank you!

matias9927

Changes look good, thanks for doing this!

matias9927 · 2025-06-17T15:54:23Z

src/hotspot/share/oops/constantPool.hpp

+  u2 _bootstrap_method_index;
+  u2 _argument_count;
+
+  const u2* argument_indexes() const {


I agree with Lois that some comments here would be useful. I think the original comment can stay where it is and you can add some extra details here.

sspitsyn

It is nice update and refactoring in general.

sspitsyn · 2025-06-18T02:28:32Z

src/hotspot/share/oops/constantPool.cpp

-      k2 = cp2->operand_argument_index_at(idx2, j);
+      k1 = bsm_attribute_entry(idx1)->argument_index(j);
+      k2 = cp2->bsm_attribute_entry(idx2)->argument_index(j);
      match = compare_entry_to(k1, cp2, k2);


Nit: I'd suggest to define two locals to simplify the code as below:

BSMAttributeEntry* e1 = bsm_attribute_entry(idx1); BSMAttributeEntry& e2 = cp2->bsm_attribute_entry(idx12); int k1 = e1->bootstrap_method_index(); int k2 = e2->bootstrap_method_index(); bool match = compare_entry_to(k1, cp2, k2); if (!match) { return false; } int argc = e1->argument_count(); if (argc == e2->argument_count()) { for (int j = 0; j < argc; j++) { k1 = e1->argument_index(j); k2 = e2->argument_index(j); match = compare_entry_to(k1, cp2, k2);

Yeah, that's a good simplification.

sspitsyn · 2025-06-18T02:31:57Z

src/hotspot/share/prims/jvmtiClassFileReconstituter.cpp

 #include "interpreter/bytecodeStream.hpp"
 #include "memory/universe.hpp"
+#include "oops/constantPool.hpp"
 #include "oops/constantPool.inline.hpp"


The line 28 is not needed as we already have line 29.

sspitsyn · 2025-06-18T02:47:45Z

src/hotspot/share/prims/jvmtiRedefineClasses.cpp


  for (int i = 0; i < argc; i++) {
-    u2 old_arg_ref_i = scratch_cp->operand_argument_index_at(old_bs_i, i);
+    u2 old_arg_ref_i = scratch_cp->bsm_attribute_entry(old_bs_i)->argument_index(i);


Nit: Could you, consider below for a code simplification? :

BSMAttributeEntry* old_bsme = scratch_cp->bsm_attribute_entry(old_bs_i); . . . 665 u2 old_ref_i = old_bsme->bootstrap_method_index(); . . . 679 u2 argc = old_bsme->argument_count(); . . . 686 u2 old_arg_ref_i = old_bsme->argument_index(i);

jdksjolen · 2025-06-18T12:33:19Z

Thank you for the reviews! I applied your comments, will await GHA before integration (also need a re-approval).

sspitsyn · 2025-06-18T17:51:14Z

src/hotspot/share/oops/constantPool.cpp

+  BSMAttributeEntry* e1 = bsm_attribute_entry(idx1);
+  BSMAttributeEntry* e2 = bsm_attribute_entry(idx2);
+  int k1 = e1->bootstrap_method_index();
+  int k2 = cp2->e2->bootstrap_method_index();


I'm kind of confused, this does not look right. It is event not going to be compiled.
It is supposed to be as below:

BSMAttributeEntry* e2 = cp2->bsm_attribute_entry(idx2); . . . int k2 = e2->bootstrap_method_index(); . . . if (argc == e2->argument_count()) { . . . k2 = e2->argument_index(j);

Gah, I accidentally made a mistake with the refactoring. Of course, when I pushed I thought "this change is so simple, no need to check it before pushing" :-). Let me fix that (and compile it myself this time)

It's okay unless you have not integrated the update. :)
Submitting at least 3 first mach5 tiers before integration will keep you out of potential trouble.

sspitsyn

Thank you for the update. The fix looks good.
I've posted one more nit though.

sspitsyn · 2025-06-19T07:33:46Z

src/hotspot/share/prims/jvmtiClassFileReconstituter.cpp

    write_u2(num_bootstrap_arguments);
    for (int arg = 0; arg < num_bootstrap_arguments; arg++) {
-      u2 bootstrap_argument = cpool()->operand_argument_index_at(n, arg);
+      u2 bootstrap_argument = cpool()->bsm_attribute_entry(n)->argument_index(arg);


Nit: This line can also use the bsme local: u2 bootstrap_argument = bsme->argument_index(arg);
Sorry, I missed this before.

Thanks, fixed.

sspitsyn · 2025-06-19T09:00:15Z

src/hotspot/share/cds/aotConstantPoolResolver.cpp


    int bsms_attribute_index = cp->bootstrap_methods_attribute_index(cp_index);
-    int arg_count = cp->operand_argument_count_at(bsms_attribute_index);
+    int arg_count = cp->bsm_attribute_entry(bsms_attribute_index)->argument_count();


Your fix made it possible to do a bit more simplifications.
For instance, each bsms_attribute_index parameter can be replaced with a bsme parameter.
But this does not look that important at the moment.

jdksjolen · 2025-06-23T07:04:20Z

/integrate

Thank you all for the reviews!

openjdk · 2025-06-23T07:05:35Z

Going to push as commit 3d35b40.
Since your change was applied there have been 584 commits pushed to the master branch:

de34bb8: 8359687: Use PassFailJFrame for java/awt/print/Dialog/DialogType.java
620df7e: 8359801: RISC-V: Simplify Interpreter::profile_taken_branch
6b43939: 8359270: C2: alignment check should consider base offset when emitting arraycopy runtime call
... and 581 more: https://git.openjdk.org/jdk/compare/13b3541467aa91c2e0ad4da70efdb25b7334d3fe...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-06-23T07:05:44Z

@jdksjolen Pushed as commit 3d35b40.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

Introduce BSMAttributeEntry

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openjdk bot added the serviceability serviceability-dev@openjdk.org label May 19, 2025

openjdk bot added the hotspot hotspot-dev@openjdk.org label May 19, 2025

jdksjolen changed the title ~~Introduce BSMAttributeEntry~~ 8357220 May 19, 2025

openjdk bot changed the title ~~8357220~~ 8357220: Introduce a BSMAttributeEntry struct May 19, 2025

jdksjolen marked this pull request as ready for review May 19, 2025 10:03

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8357220: Introduce a BSMAttributeEntry struct #25298

8357220: Introduce a BSMAttributeEntry struct #25298

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