RFR: 8256486: Linux/Windows-x86 builds broken after JDK-8254231 [v4]

[David Holmes]

On Mon, 23 Nov 2020 20:36:11 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> JDK-8254231 breaks the Linux and Windows x86 (32-bit) builds. This contains the needed changes to get it working again.
>> 
>> Perhaps the most interesting change is adding the `JNI_ENTRY_CPP_NOENV` macro. Using just JNI_ENTRY was causing a linkage failure, due to the declaration of the function in the class not having the same linkage specifiers. It looks like we can't just specify C linkage for class member functions.
>> 
>> However, in this case C linkage is not required, so I've added the new macro which doesn't have `extern "C"`. I've also dropped the `JNIEnv*` parameter, since it was not being used, but causing extra work for the caller.
>> 
>> Other than that, it's just about adding default definitions for missing functions, and moving around some code in MacroAssembler to be in the correct `#ifdef` blocks.
>> 
>> Testing: `make images` on Linux and Windows x86_32 platforms.
>
> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use the Unimplemented() macro instead of hlt()

Hi Jorn,

Sorry but I don't agree with the addition of JNI_ENTRY_CPP_NOENV. I think there is a flaw in the way these methods are exposed/structured. See comment below.

Thanks,
David

src/hotspot/share/prims/universalUpcallHandler.cpp line 36:

> 34: extern struct JavaVM_ main_vm;
> 35: 
> 36: JNI_ENTRY_CPP_NOENV(void, ProgrammableUpcallHandler::upcall_helper(jobject rec, address buff))

I do not like this. I think you have a design flaw here. We should not be directly calling member functions like this from other native code! The entry point should be a simple C-linkage function that is a normal JNI_ENTRY (assuming it actually should be a JNI_ENTRY and not JVM_ENTRY?) and that can then call the true target.

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

Changes requested by dholmes (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1266