RFR: 8359707: Add classfile modification code to RedefineClassHelper [v8]

[David Holmes]

On Fri, 27 Jun 2025 11:37:30 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> I copied this code for another test in the Valhalla repo and thought it would be a good utility function.  It might be better written using the Classfile API.
>> Tested with test.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Rename replaceAllStrings to replaceClassName and add back the byte buffer version of the function.

Changes requested by dholmes (Reviewer).

test/hotspot/jtreg/serviceability/jvmti/RedefineClasses/ClassVersionAfterRedefine.java line 56:

> 54:         // redefining the original version of "TestClassXXX" (i.e. "TestClassOld").
> 55:         buf = RedefineClassHelper.replaceClassName(cvar, "TestClassNew", "TestClassXXX");
> 56:         // Now redine the original version of "TestClassXXX" (i.e. "TestClassOld").

Suggestion:

        // Now redefine the original version of "TestClassXXX" (i.e. "TestClassOld").

Pre-existing

test/lib/RedefineClassHelper.java line 85:

> 83:      * @param bytes in original class file.
> 84:      * @param oldClassName old class name.
> 85:      * @param newClassName new class name to replace with old class name.

Suggestion:

     * @param newClassName new class name to replace the old class name.

test/lib/RedefineClassHelper.java line 87:

> 85:      * @param newClassName new class name to replace with old class name.
> 86:      */
> 87:     public static byte[] replaceClassName(byte[] bytes, String oldClassName, String newClassName) throws Exception {

Just realized that `oldClassName` is not actually used. Suggestion:

/*
 * Copy the class defined by `bytes`, replacing the name of the class with `newClassName`, so that both
 * old and new classes can be compiled by jtreg for the test.
 *
 * @param bytes the bytes presenting the original classfile
 * @param newClassName the new class name for the returned class representation
 * @ return a copy of the class represented by `bytes` but with the name `newClassName`
 */
 public static byte[] replaceClassName(byte[] bytes, String newClassName) throws Exception {

-------------

PR Review: https://git.openjdk.org/jdk/pull/25857#pullrequestreview-2969920311
PR Review Comment: https://git.openjdk.org/jdk/pull/25857#discussion_r2174234229
PR Review Comment: https://git.openjdk.org/jdk/pull/25857#discussion_r2174235361
PR Review Comment: https://git.openjdk.org/jdk/pull/25857#discussion_r2174242441