[foreign-memaccess+abi] RFR: 8263459: Add better support for restricted methods

[Maurizio Cimadamore]

On Fri, 19 Mar 2021 11:53:16 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> --enable-native-access command line option
>
> I've already reviewed the code separately and provided some commments which have been addressed here. It would be great if somebody from the VM team could go over the VM changes. Added some minor comments.

For the records, the approach implemented in this patch works as follows: when a Panama native restricted method is called, we will no require that the caller module (which could be ALL-UNNAMED) has been whitelisted accordingly, on the command line, using this flag:

--enable-native-access=<modulename>

In other words, this work replaces the hacky `-Dforeign.restricted=permit` property with a system which works in tandem with the Java module system.

While the support is relatively minimal, we have spent some cycles to add a new jlink plugin which will search a module for all calls to restricted methods and, if any is found, will mark the module-info.class as "native" with a special classfile attribute.

At startup, if the runtime sees that the module graph contains one or more modules that are marked as "native" but whose command line flag has not been set, an error will occur immediately - otherwise, w/o jlink, an error will only occur when a restricted method is called.

Changes to javadoc and jshell will come as a separate patch - the idea is to for for native restricted methods something similar as to what has been done in javadoc for preview API methods.

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

PR: https://git.openjdk.java.net/panama-foreign/pull/471