RFR: 8353197: Document preconditions for JavaLangAccess methods

[Chen Liang]

On Thu, 1 May 2025 05:33:29 GMT, Volkan Yazici <vyazici at openjdk.org> wrote:

> Document preconditions on certain `JavaLangAccess` methods that use operations either unsafe and/or without range checks.

src/java.base/share/classes/jdk/internal/access/JavaLangAccess.java line 315:

> 313:      * <b>WARNING: The caller of this method shall relinquish and transfer the
> 314:      * ownership of the byte array to the callee</b>, since the later will not
> 315:      * make a copy.

I think we should add a note on why no copy is made - there may be multiple reads to the input array for decoding, so the input array must not be accessible by untrusted code, which can racily modify it. A side effect is that this array is simply reused if it's eligible to be the string content array, which is unfortunately abused in a few places in the JDK.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24982#discussion_r2070244058