8375534: Debug method 'pp' should support compressed oops

[TobiHartmann]

The debug method pp is currently not able to handle compressed oops. This should fix it. The code is similar to BlockLocationPrinter<CollectedHeapT>::print_location.

Before:

(rr) call (void*) pp(0x6b9c08fc8)

"Executing pp"
java.lang.Runtime$Version 
{0x00000006b9c08fc8} - klass: 'java/lang/Runtime$Version' - flags: 

 - ---- fields (total size 4 words):
 - private final value 'version' 'Ljava/util/List;' @12  a 'java/util/ImmutableCollections$List12'{0x00000006b9c2cbb8} (0xd7385977)
 - private final value 'pre' 'Ljava/util/Optional;' @16  a 'java/util/Optional'{0x00000006b9c2cbd0} (0xd738597a)
 - private final value 'build' 'Ljava/util/Optional;' @20  a 'java/util/Optional'{0x00000006b9c0a118} (0xd7381423)
 - private final value 'optional' 'Ljava/util/Optional;' @24  a 'java/util/Optional'{0x00000006b9c2cbe8} (0xd738597d)
$1 = (void *) 0x0
(rr) call (void*) pp(0xd7381423)

"Executing pp"
The program being debugged received signal SIGSEGV, Segmentation fault
while in a function called from GDB.  GDB has restored the context
to what it was before the call.  To change this behavior use
"set unwind-on-signal off".  Evaluation of the expression containing
the function (pp(long)) will be abandoned.

After:

"Executing pp"
java.lang.Runtime$Version 
{0x00000006b9c08fc8} - klass: 'java/lang/Runtime$Version' - flags: 

 - ---- fields (total size 4 words):
 - private final value 'version' 'Ljava/util/List;' @12  a 'java/util/ImmutableCollections$List12'{0x00000006b9c2cbb8} (0xd7385977)
 - private final value 'pre' 'Ljava/util/Optional;' @16  a 'java/util/Optional'{0x00000006b9c2cbd0} (0xd738597a)
 - private final value 'build' 'Ljava/util/Optional;' @20  a 'java/util/Optional'{0x00000006b9c0a118} (0xd7381423)
 - private final value 'optional' 'Ljava/util/Optional;' @24  a 'java/util/Optional'{0x00000006b9c2cbe8} (0xd738597d)
$1 = (void *) 0x0
(rr) call (void*) pp(0xd7381423)

"Executing pp"
3610776611 is a compressed pointer to object: java.util.Optional 
{0x00000006b9c0a118} - klass: 'java/util/Optional' - flags: 

 - ---- fields (total size 3 words):
 - private final value 'value' 'Ljava/lang/Object;' @16  null (0x00000000)
$2 = (void *) 0x0

Thanks,
Tobias

---

Progress

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Issue

• JDK-8375534: Debug method 'pp' should support compressed oops (Enhancement - P4)

Reviewers

• Vladimir Ivanov (@iwanowww - Reviewer)
• Paul Hübner (@Arraying - Author)

Reviewing

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[bridgekeeper]

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[openjdk]

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

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

8375534: Debug method 'pp' should support compressed oops

Reviewed-by: vlivanov, phubner

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At the time when this comment was updated there had been 209 new commits pushed to the master branch:

• 560a92a: 8375787: compiler/vectorapi/TestCastShapeBadOpc.java fails with release VMs
• b5727d2: 8375738: Fix -Wzero-as-null-pointer-constant warnings in MacOSX/bsd code
• 34d6e5e: 8375737: Fix -Wzero-as-null-pointer-constant warnings in arm32 code
• ... and 206 more: https://git.openjdk.org/jdk/compare/de81d38995356a2e8528a419ebd445e79cd136d1...master

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[openjdk]

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[mlbridge]

Webrevs

• 01: Full - Incremental (c4b67195)
• 00: Full (d09f09ca)

[iwanowww]

Overall, looks good.

BlockLocationPrinter<CollectedHeapT>::print_location() has very similar code, but uses a more elaborate check in place of Universe::heap()->is_in(o). Any particular reason LocationPrinter::is_valid_obj() doesn't fit pp()? Otherwise, it makes sense to unify the code.

[TobiHartmann]

Thanks for the review, Vladimir. You are right and when looking at the code again, I noticed that we can just call Universe::heap()->print_location from pp. I'm not so sure anymore how valuable pp really is, given that there is find which entails the functionality of pp. But let's fix it for now.

[Arraying]

This is a super useful change, thanks for doing it. One small comment.

[Arraying]

FYI, we also have os::print_location which adds a few extra goodies (nullcheck + code blob check). Its documentation mentions

// moved from debug.cpp (used to be find()) but still called from there

I'm happy with the current code and I'd also be okay with using the os version, I just wanted to point it out in case you think one is more appropriate than the other.

[TobiHartmann]

Thanks for taking a look at this. Yes, I've seen that and it's already used by find and findpc. I think the intention of pp is that we already know/expect that the argument is a pointer into the Java heap and therefore want to limit the amount of checks (maybe for performance or stability reasons?) during debugging.

[iwanowww]

Looks good.

[franciscoarturorivera371-cyber]

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[TobiHartmann]

Thanks Vladimir!

[TobiHartmann]

/integrate

[openjdk]

Going to push as commit 0f4d775.
Since your change was applied there have been 219 commits pushed to the master branch:

• 38a8309: 8341630: G1: Adopt PartialArrayState to consolidate marking stack in concurrent marking
• 3d919ad: 8373366: HandshakeState should disallow suspend ops for disabler threads
• a0ac5b3: 8375775: JDK 26 RDP2 L10n resource files update
• ... and 216 more: https://git.openjdk.org/jdk/compare/de81d38995356a2e8528a419ebd445e79cd136d1...master

Your commit was automatically rebased without conflicts.

[openjdk]

@TobiHartmann Pushed as commit 0f4d775.

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