RFR: 8361842: Move input validation checks to Java for java.lang.StringCoding intrinsics [v13]

[Volkan Yazici]

On Fri, 25 Jul 2025 07:40:46 GMT, Volkan Yazici <vyazici at openjdk.org> wrote:

>> Validate input in `java.lang.StringCoding` intrinsic Java wrappers, improve their documentation, enhance the checks in the associated IR or assembly code, and adapt them to cause VM crash on invalid input.
>> 
>> ## Implementation notes
>> 
>> The goal of the associated umbrella issue [JDK-8156534](https://bugs.openjdk.org/browse/JDK-8156534) is to, for `java.lang.String*` classes,
>> 
>> 1. Move `@IntrinsicCandidate`-annotated `public` methods<sup>1</sup> (in Java code) to `private` ones, and wrap them with a `public` ["front door" method](https://github.com/openjdk/jdk/pull/24982#discussion_r2087493446)
>> 2. Since we moved the `@IntrinsicCandidate` annotation to a new method, intrinsic mappings – i.e., associated `do_intrinsic()` calls in `vmIntrinsics.hpp` – need to be updated too
>> 3. Add necessary input validation (range, null, etc.) checks to the newly created public front door method
>> 4. Place all input validation checks in the intrinsic code (add if missing!) behind a `VerifyIntrinsicChecks` VM flag
>> 
>> Following preliminary work needs to be carried out as well:
>> 
>> 1. Add a new `VerifyIntrinsicChecks` VM flag
>> 2. Update `generate_string_range_check` to produce a `HaltNode`.  That is, crash the VM if `VerifyIntrinsicChecks` is set and a Java wrapper fails to spot an invalid input.
>> 
>> <sup>1</sup>  `@IntrinsicCandidate`-annotated constructors are not subject to this change, since they are a special case.
>> 
>> ## Functional and performance tests
>> 
>> - `tier1` (which includes `test/hotspot/jtreg/compiler/intrinsics/string`) passes on several platforms. Further tiers will be executed after integrating reviewer feedback.
>> 
>> - Performance impact is still actively monitored using `test/micro/org/openjdk/bench/java/lang/String{En,De}code.java`, among other tests. If you have suggestions on benchmarks, please share in the comments.
>> 
>> ## Verification of the VM crash
>> 
>> I've tested the VM crash scenario as follows:
>> 
>> 1. Created the following test program:
>> 
>> public class StrIntri {
>>     public static void main(String[] args) {
>>         Exception lastException = null;
>>         for (int i = 0; i < 1_000_000; i++) {
>>             try {
>>                 jdk.internal.access.SharedSecrets.getJavaLangAccess().countPositives(new byte[]{1,2,3}, 2, 5);
>>             } catch (Exception exception) {
>>                 lastException = exception;
>>             }
>>         }
>>         if (lastException != null) {
>>             lastException.printStackTrace...
>
> Volkan Yazici has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 31 additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'upstream/master' into strIntrinCheck
>  - Replace `requireNonNull` with implicit null checks to reduce bytecode size
>  - Add `@bug` tags
>  - Improve wording of `@param len`
>  - Make source array bound checks lenient too
>  - Cap destination array bounds
>  - Fix bit shifting
>  - Remove superseded `@throws` Javadoc
>  - Merge remote-tracking branch 'upstream/master' into strIntrinCheck
>  - Make `StringCoding` encoding intrinsics lenient
>  - ... and 21 more: https://git.openjdk.org/jdk/compare/8888d41d...c322f0e0

Status update:

* Changes are pretty-much settled. I'm waiting for a final review from @cl4es.
* Checked the performance impact of changes against [DaCapo](https://www.dacapobench.org/) BioJava, and `org.openjdk.bench.java.lang.String{En,De}code` benchmarks on several platforms. Spotted one consistent significant (i.e., >2%) regression: `StringDecode::decodeShortMixed` – explicitly forcing inlining<sup>1</sup> did not help either. Granted this is the only, and benchmark- and platform-specific regression, @RogerRiggs suggested creating a follow-up ticket for this particular regression and integrating this PR. I will wait for input from @cl4es.

<sup>1</sup> `-XX:CompileCommand=inline,java.lang.StringCoding::encodeISOArray -XX:CompileCommand=inline,java.lang.StringCoding::encodeAsciiArray`

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PR Comment: https://git.openjdk.org/jdk/pull/25998#issuecomment-3126372979