RFR: 8361842: Move input validation checks to Java for String-related intrinsics [v8]

[Raffaello Giulietti]

On Thu, 17 Jul 2025 07:20:34 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 incrementally with one additional commit since the last revision:
> 
>   Replace casting with `as_Region()` in `generate_string_range_check`

src/java.base/share/classes/java/lang/StringCoding.java line 130:

> 128:      * <p>
> 129:      * This method assumes that {@code sa} is encoded in UTF-16, and hence,
> 130:      * each {@code char} maps to 2 bytes.

Since `sa` is assumed to be encoded in UTF-16, what's the point of the previous paragraph?

src/java.base/share/classes/java/lang/StringCoding.java line 132:

> 130:      * each {@code char} maps to 2 bytes.
> 131:      * </p><p>
> 132:      * {@code sp} is encoded in ISO-8859-1. There each {@code byte} corresponds

As this is an index, it doesn't make sense to state that it is encoded in ISO-8859-1.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25998#discussion_r2213428956
PR Review Comment: https://git.openjdk.org/jdk/pull/25998#discussion_r2213429091