RFR: 8331671: Implement JEP 472: Prepare to Restrict the Use of JNI [v2]

[Maurizio Cimadamore]

On Mon, 13 May 2024 11:38:40 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> This PR implements [JEP 472](https://openjdk.org/jeps/472), by restricting the use of JNI in the following ways:
>> 
>> * `System::load` and `System::loadLibrary` are now restricted methods
>> * `Runtime::load` and `Runtime::loadLibrary` are now restricted methods
>> * binding a JNI `native` method declaration to a native implementation is now considered a restricted operation
>> 
>> This PR slightly changes the way in which the JDK deals with restricted methods, even for FFM API calls. In Java 22, the single `--enable-native-access` was used both to specify a set of modules for which native access should be allowed *and* to specify whether illegal native access (that is, native access occurring from a module not specified by `--enable-native-access`) should be treated as an error or a warning. More specifically, an error is only issued if the `--enable-native-access flag` is used at least once.
>> 
>> Here, a new flag is introduced, namely `illegal-native-access=allow/warn/deny`, which is used to specify what should happen when access to a restricted method and/or functionality is found outside the set of modules specified with `--enable-native-access`. The default policy is `warn`, but users can select `allow` to suppress the warnings, or `deny` to cause `IllegalCallerException` to be thrown. This aligns the treatment of restricted methods with other mechanisms, such as `--illegal-access` and the more recent `--sun-misc-unsafe-memory-access`.
>> 
>> Some changes were required in the package-info javadoc for `java.lang.foreign`, to reflect the changes in the command line flags described above.
>
> Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Avoid call to VM::isModuleSystemInited
>   Use initial error stream

src/java.base/share/classes/jdk/internal/reflect/Reflection.java line 124:

> 122:         if (module != null) {
> 123:             // not in init phase
> 124:             Holder.JLA.ensureNativeAccess(module, owner, methodName, currentClass);

In an earlier iteration I had a call to `VM::isModuleSystemInited`, but I discovered that caused a performance regression, since that method involves a volatile access. Perhaps we should rethink that part of the init code to use stable fields, but it's probably better done separately.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19213#discussion_r1598328283