RFR: 8344560: Add system property for patched runtime

[Jaikiran Pai]

On Wed, 20 Nov 2024 14:26:27 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

> Please review this simple patch which adds a new external system property `jdk.patched` when the runtime has been patched with the `--patch-module` switch. This is useful for two reasons: 1) it allows one to determine at run-time whether or not `--patch-module` has been used (by querying the said property) 2) allows tools, such as `jlink` doing the same without needing to expose internal properties the JVM sets on initialization.
> 
> Testing:
> 
> - [x] GHA (includes new test)
> - [x] New jtreg test 
> 
> Thoughts?

src/hotspot/share/runtime/arguments.cpp line 2272:

> 2270:       if (res == JNI_OK) {
> 2271:         // Add jdk.patched system property when processing of args was OK
> 2272:         PropertyList_unique_add(&_system_properties, "jdk.patched", "true",

Hello Severin, in addition, should we explicitly set this system property to `false` (or remove the system property) when `--patch-module` isn't used? I think that would then prevent applications from passing `-Djdk.patched=true` when the runtime hasn't been patched. 
While at it, should there be additional guards to prevent applications from changing the value of this system property by doing `System.setProperty("jdk.patched")` at runtime?

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PR Review Comment: https://git.openjdk.org/jdk/pull/22277#discussion_r1851376171