[jdk18] RFR: 8279011: JFR: JfrChunkWriter incorrectly handles int64_t chunk size as size_t

[Aleksey Shipilev]

See the investigation in the bug.

Spot the problem:


int64_t JfrChunkWriter::write_chunk_header_checkpoint(bool flushpoint) {
   ...
   const size_t sz_written = size_written(); // <-- returns int64_t
   write_be_at_offset(sz_written, chunk_size_offset); // <--- template instantiation with type=size_t
   return sz_written;
 }


This would have been nearly fine -- small `size_t` -> `int64_t` conversion is okay value-wise. But `write_be_at_offset` calculates the position for the writeout using `sizeof(T)`, which silently borks the whole thing on at least 32-bit platforms, where `sizeof(size_t)` != `sizeof(int64_t)`. 

Additional testing:
 - [x] Linux x86_64 `jdk_jfr` (no regressions)
 - [x] Linux x86_32 `jdk_jfr` (many failing tests now pass)

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

Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk18/pull/50/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=50&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279011
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/50.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/50/head:pull/50

PR: https://git.openjdk.java.net/jdk18/pull/50