8354323: Safeguard SwitchBootstraps.typeSwitch when used outside the compiler #25090

biboudis · 2025-05-07T11:57:02Z

While the compiler does not allow invalid queries to flow into SwitchBootstraps:typeSwitch, a library user could do that and typeSwitch does not prevent such usage pattern errors resulting in erroneous evaluation.

For example this is not valid Java (and protected) by javac:

byte b = 1;
switch (b) {
    case String s -> System.out.println("How did we get here? byte is " + s.getClass());
}

but this is a valid call (and not protected):

CallSite shortSwitch = SwitchBootstraps.typeSwitch(
    MethodHandles.lookup(), 
    "", 
    MethodType.methodType(int.class, short.class, int.class),  // models (short, int) -> int
    String.class);

The SwitchBootstraps.typeSwitch returns wrong result since the code was reasoning erroneously that this pair was unconditionally exact.

This PR proposes to add the safety check in unconditional exactness which will return false in erroneous pairs and then the actual check will be delegated to instanceof. For the case of erroneous pairs with primitive booleans there is a check in the beginning of the type switch skeleton.

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Issue

JDK-8354323: Safeguard SwitchBootstraps.typeSwitch when used outside the compiler (Bug - P4)

Reviewers

Chen Liang (@liach - Reviewer) Review applies to 835fb6ab
Jan Lahoda (@lahodaj - Reviewer)

Reviewing

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$ git fetch https://git.openjdk.org/jdk.git pull/25090/head:pull/25090
$ git checkout pull/25090

Update a local copy of the PR:
$ git checkout pull/25090
$ git pull https://git.openjdk.org/jdk.git pull/25090/head

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$ git pr checkout 25090

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https://git.openjdk.org/jdk/pull/25090.diff

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…compiler

bridgekeeper · 2025-05-07T11:57:39Z

👋 Welcome back abimpoudis! 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 · 2025-05-07T11:58:51Z

@biboudis 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:

8354323: Safeguard SwitchBootstraps.typeSwitch when used outside the compiler

Reviewed-by: jlahoda, liach

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 304 new commits pushed to the master branch:

50a7755: 8347530: Improve error message with invalid permits clauses
50e873f: 8356455: ZGC: Replace ZIntrusiveRBTree with IntrusiveRBTree
74fc4e4: 8357179: Deprecate VFORK launch mechanism from Process implementation (linux)
... and 301 more: https://git.openjdk.org/jdk/compare/995d54161fed657f38753813f55d0591e77a42e3...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

openjdk · 2025-05-07T11:59:27Z

@biboudis The following label will be automatically applied to this pull request:

core-libs

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

mlbridge · 2025-05-07T12:02:25Z

Webrevs

liach · 2025-05-07T16:36:09Z

src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java

+                        cb.goto_(next);
+                        continue;
+                    }
+                    else if (unconditionalExactnessCheck(selectorType, classLabel)) {


Can we merge this into isNotValidPair(...) || unconditionalExactnessCheck(...) then do nothing? The next label is already in theory immediately bound to the instruction after goto.

The empty body means that we unconditionally return the index case 0 -> /*no if is generated*/ return 0;.

I confirmed that by merging, the following test would not pass. It returns erroneously 0, instead of 1.

testPrimitiveType((byte) 1, byte.class,0, 1, boolean.class, byte.class);

liach

looks good!

lukellmann · 2025-05-11T21:45:46Z

src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java

+                (targetType.isPrimitive() && selectorType.isPrimitive() &&
+                    ((selectorType.equals(byte.class) && !targetType.equals(char.class)) ||


Will unconditionalExactnessMatch(byte.class, boolean.class return true? I think it shouldn't, even if isNotValidPair is called before.

unconditionalExactnessMatch needs to return an answer whether a pair is unconditional assuming it is applicable. Fusing them would need to elaborate the type of the returned answer.

mcimadamore · 2025-05-12T09:15:56Z

src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java

+                     (selectorType.equals(short.class) && (selectorWrapper.isStrictSubRangeOf(targetWrapper))) ||
+                     (selectorType.equals(char.class)  && (selectorWrapper.isStrictSubRangeOf(targetWrapper)))  ||
+                     (selectorType.equals(int.class)   && (targetType.equals(double.class) || targetType.equals(long.class))) ||
+                     (selectorType.equals(float.class) && (selectorWrapper.isStrictSubRangeOf(targetWrapper)))))) return true;


Is double the only allowed target for float ? If so, perhaps we could simplify like for other selector types.
Or, alternatively, I wonder if it wouldn't be simpler to always check for strict subrange on the wrappers, but then ban the conversions that are not exact (e.g. int -> float), as those are few?

Thanks @mcimadamore. I gave it a shot, despite the fact that it touches the mirrored code in Types because it is a good recommendation. But please take a look again since it is a very central part: a7c4e39

mcimadamore · 2025-05-12T09:16:30Z

src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java

@@ -717,6 +721,11 @@ private static Consumer<CodeBuilder> generateTypeSwitchSkeleton(Class<?> selecto
        };
    }

+    private static boolean isNotValidPair(Class<?> selectorType, Object caseLabel) {
+        return (selectorType == boolean.class && caseLabel != boolean.class && caseLabel != Boolean.class) ||


What happens if caseLabel is a reference class? E.g. a boolean selector is incompatible with String.

(selectorType == boolean.class && caseLabel != boolean.class && caseLabel != Boolean.class) -> true so it is not a valid pair. Do you think it is wrong?

e.g., 7b030be

lahodaj

Looks reasonable to me.

biboudis · 2025-05-22T08:35:58Z

/integrate

openjdk · 2025-05-22T08:36:47Z

Going to push as commit c0665ef.
Since your change was applied there have been 340 commits pushed to the master branch:

85b24c3: 8350869: os::stat doesn't follow symlinks on Windows
d9b6e4b: 8352642: Set zipinfo-time=false when constructing zipfs FileSystem in com.sun.tools.javac.file.JavacFileManager$ArchiveContainer for better performance
e348aa0: 8351958: Some compile commands should be made diagnostic
... and 337 more: https://git.openjdk.org/jdk/compare/995d54161fed657f38753813f55d0591e77a42e3...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-05-22T08:36:55Z

@biboudis Pushed as commit c0665ef.

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

8354323: Safeguard SwitchBootstraps.typeSwitch when used outside the …

835fb6a

…compiler

openjdk bot added the rfr Pull request is ready for review label May 7, 2025

openjdk bot added the core-libs [email protected] label May 7, 2025

liach reviewed May 7, 2025

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liach approved these changes May 7, 2025

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lukellmann reviewed May 11, 2025

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mcimadamore reviewed May 12, 2025

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Add test for boolean selector and String case label

7b030be

openjdk bot removed the ready Pull request is ready to be integrated label May 13, 2025

Simplify unconditional exactness in both Types and SwitchBootstraps

a7c4e39

lahodaj approved these changes May 21, 2025

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openjdk bot added the integrated Pull request has been integrated label May 22, 2025

openjdk bot closed this May 22, 2025

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels May 22, 2025

		(targetType.isPrimitive() && selectorType.isPrimitive() &&
		((selectorType.equals(byte.class) && !targetType.equals(char.class)) \|\|

8354323: Safeguard SwitchBootstraps.typeSwitch when used outside the compiler #25090

8354323: Safeguard SwitchBootstraps.typeSwitch when used outside the compiler #25090

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