Update JNI Target relocation record to have offset to the reloLocation.

[dsouzai]

On x86, the JNI Target relocation puts the incorrect address when
generating a Runtime Assumption. However, the address that the
relocation infra itself needs to patch is correct. Thus, the relo record
has to hold not just the location to patch but also the location to
register the assumption against. This is the same on most platforms, but
different on x86.

eclipse-openj9/openj9#14421 depends on this change; OpenJ9 will be broken without a coordinated merge.

[mstoodle]

the changes look ok to me, given what's in the OpenJ9 pull request.

[mstoodle]

did you want to add the < 256 assertion here as well as in OpenJ9 when the actual relocation record is created? I could understand if not (you could view as a requirement imposed by a downstream component) but given it's JNI and likely not to be reused by anything else, maybe catching a problem here is desirable? I'll leave it as optional, because I can see it both ways.

[dsouzai]

I was thinking about it, but I think I mainly didn't add it here it so that there if, for whatever reason (perhaps on a different platform) the offset had to be increased to fit in a bigger type, then there would have to be an OMR PR just to update the assert. As such I figured it's probably best to just have the assert close to where the data in the relo header is actually stored.

[mstoodle]

jenkins build all

[mstoodle]

hm, guess I could have only tested x86 and z...oh well :(

[dsouzai]

Windows build error is because of a warning that's treated as an error, namely:

[2022-02-03T14:28:09.333Z]          C:\jenkins\workspace\PullRequest-win_x86-64\Build\compiler\x\codegen\X86BinaryEncoding.cpp(1103): warning C4345: behavior change: an object of POD type constructed with an initializer of the form () will be default-initialized [C:\jenkins\workspace\PullRequest-win_x86-64\Build\build\jitbuilder\jitbuilder.vcxproj]

This is because of the line

TR_RelocationRecordInformation *info = new (comp->trHeapMemory()) TR_RelocationRecordInformation();

MSVC does not like the fact that TR_RelocationRecordInformation is a POD object and we're calling the empty constructor on it which will be default initialized. I guess I have to use the other way of allocating this object, namely:

TR_RelocationRecordInformation *info = 
   reinterpret_cast<TR_RelocationRecordInformation *>(
      comp->trMemory()->allocateHeapMemory(sizeof(TR_RelocationRecordInformation));

[mstoodle]

I think you could also just new it without the trailing () if it's a POD, but using allocateHeapMemory() certainly works.

[mstoodle]

jenkins build all