RFR: 8282191: Implementation of Foreign Function & Memory API (Preview) [v37]

[Maurizio Cimadamore]

On Wed, 4 May 2022 16:47:28 GMT, ExE Boss <duke at openjdk.java.net> wrote:

>> Maurizio Cimadamore has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 57 commits:
>> 
>>  - Merge branch 'master' into foreign-preview
>>  - Update src/java.base/share/classes/jdk/internal/misc/X-ScopedMemoryAccess.java.template
>>    
>>    Co-authored-by: ExE Boss <3889017+ExE-Boss at users.noreply.github.com>
>>  - Tweak support for Linker lookup
>>    Improve javadoc of SymbolLookup
>>  - Tweak Addressable javadoc
>>  - Downcall and upcall tests use wrong layout which is missing some trailing padding
>>  - Simplify libraryLookup impl
>>  - Address CSR comments
>>  - Merge branch 'master' into foreign-preview
>>  - Add ValueLayout changes
>>  - Tweak support for array element var handle
>>  - ... and 47 more: https://git.openjdk.java.net/jdk/compare/af1ee1cc...41d055ab
>
> src/java.base/share/classes/java/lang/foreign/SymbolLookup.java line 153:
> 
>> 151:     static SymbolLookup loaderLookup() {
>> 152:         Class<?> caller = Reflection.getCallerClass();
>> 153:         ClassLoader loader = Objects.requireNonNull(caller.getClassLoader());
> 
> Shouldn’t this be changed to throw `IllegalCallerException` instead of throwing `NullPointerException` when the `caller`’s `ClassLoader` is `null`[^1] or when `caller` itself is `null`[^2]?
> 
> [^1]: This happens when `caller` is on the bootstrap classpath.
> [^2]: This happens when `SymbolLookup.loaderLookup()` is called by native code and no **Java** code is on the call stack.

Good points. Regarding `ClassLoader` being null, I think we can still return something using the `BootLoader`'s `NativeLibraries` object - that would allow this method to be called internally. @mlchung Can you please confirm?

As for the caller sensitive having no real caller (e.g. because method is called directly from native code), I think we should add a check in `Reflection::ensureNativeAccess`. Few weeks ago I verified that adding such a check does not compromise upcall stub created via the Linker interface (e.g. a Java upcall might require to perform restricted operations - but those operation always happen inside the upcall MH, which is always associated with some class).

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PR: https://git.openjdk.java.net/jdk/pull/7888