8366341: [BACKOUT] JDK-8365256: RelocIterator should use indexes instead of pointers

[jdksjolen]

Hi,

When a null pointer is accessed in SA it's serialized into the null Java object, this in turn causes runtime NPE:s when attempts are made to perform arithmetic on them. As we changed _immutable_data to be null when missing, this hits that corner case in the SA.

Example of code which fails:

  public PCDesc getPCDescAt(Address pc) {
    // NOTE: scopesPCsBegin() depends on the value of _immutable_data and will throw NPE if immutable_data is null
    for (Address p = scopesPCsBegin(); p.lessThan(scopesPCsEnd()); p = p.addOffsetTo(pcDescSize)) {
      PCDesc pcDesc = new PCDesc(p);
      if (pcDesc.getRealPC(this).equals(pc)) {
        return pcDesc;
      }
    }
    return null;
  }

There are similar iterators in Hotspot code, they will cause UBSAN to complain instead as we're adding something to a null pointer.

The "real fix" requires a lot of work on the SA side, and we cannot prioritize that. Instead, I'm backing out my changes.

---

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Issue

• JDK-8366341: [BACKOUT] JDK-8365256: RelocIterator should use indexes instead of pointers (Enhancement - P4)

Reviewers

• Albert Mingkun Yang (@albertnetymk - Reviewer)

Reviewing

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[openjdk]

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

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

8366341: [BACKOUT] JDK-8365256: RelocIterator should use indexes instead of pointers

Reviewed-by: ayang

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At the time when this comment was updated there had been 13 new commits pushed to the master branch:

• a5a2340: 8365053: Refresh hotspot precompiled.hpp with headers based on current frequency
• 7469a27: 8365939: [Redo] G1: Move collection set related full gc reset code into abandon_collection_set() method
• d06c66f: 8365055: G1: Merge Heap Roots phase incorrectly clears young gen remembered set every time
• ... and 10 more: https://git.openjdk.org/jdk/compare/124575b4c2b52328a8efddb40e67057a53b44a04...master

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Webrevs

• 00: Full (947c1572)

[jdksjolen]

Thanks Albert
/integrate

[openjdk]

Going to push as commit 5c78c7c.
Since your change was applied there have been 14 commits pushed to the master branch:

• b0f5b23: 8366145: G1: Help diagnose ubsan division by zero in computing pause time ratios (g1Analytics.cpp)
• a5a2340: 8365053: Refresh hotspot precompiled.hpp with headers based on current frequency
• 7469a27: 8365939: [Redo] G1: Move collection set related full gc reset code into abandon_collection_set() method
• ... and 11 more: https://git.openjdk.org/jdk/compare/124575b4c2b52328a8efddb40e67057a53b44a04...master

Your commit was automatically rebased without conflicts.

[openjdk]

@jdksjolen Pushed as commit 5c78c7c.

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