RFR: 8361842: Move input validation checks to Java for String-related intrinsics [v7]

[Volkan Yazici]

On Thu, 17 Jul 2025 06:13:30 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 two additional commits since the last revision:
> 
>  - Duplicate affected tests with `-XX:+VerifyIntrinsicChecks` variants
>  - Fix compiler error in `generate_string_range_check`

test/hotspot/jtreg/compiler/patches/java.base/java/lang/Helper.java line 44:

> 42:     @jdk.internal.vm.annotation.ForceInline
> 43:     public static int StringCodingEncodeAsciiArray0(char[] sa, int sp, byte[] da, int dp, int len) {
> 44:         return StringCoding.encodeAsciiArray0(sa, sp, da, dp, len);

`TestVerifyIntrinsicChecks` needs to have access to an intrinsic that uses the `VerifyIntrinsicChecks` VM flag. For that purpose, I chose `StringCoding::encodeAsciiArray`, which is the guarded public door to `@IntrinsicCandidate encodeAsciiArray0()` – note the `0` suffix! `TestVerifyIntrinsicChecks` needs to feed invalid input to `encodeAsciiArray0()` to trip the checks in the compiler intrinsic. Though, `encodeAsciiArray0()` is, as is one of the main motivations of this PR, private. In `TestVerifyIntrinsicChecks`, I first tried accessing to `encodeAsciiArray0()` using reflection, but this blocked the method get inlined, which is a requirement for intrinsification. Hence, I made the  `encodeAsciiArray0()` package-private and exposed it via `StringCodingEncodeAsciiArray0` to allow inlining, and, eventually, intrinsification. This worked.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25998#discussion_r2212396003