On Sat, 3 Oct 2026 23:45:18 GMT, Justus Garbe <[email protected]> wrote:
> A rare bug with the jdk has recently been filed again: > https://github.com/adoptium/adoptium-support/issues/1538, which reports the > already seen behavior in JDK-8352077: `unhandled instruction`. The original > issue was closed with no reproduction. I have managed to write a reproduction > with the new data. > > It seems that it is caused by a missing null check in the > `BreakpointInfo::set` path, which calls into: > `incr_number_of_breakpoints` which calls `build_method_counters`. Which has > multiple ways to return `nullptr` if either the oom flag is already set or > the allocation fails, which is done via allocate_no_exception since it runs > on a VMThread, therefore it cant actually call a GC or raise the metadata > limit. Therefore incr_number_of_breakpoints, never increases the number > (since method counters is nullptr). Compilation is then paused, because the > method cannot increase it's invocation counter, then after a purge caused by > a gc pass, the mark is unset. After that it can correctly create it's > counter, but since it never captured the breakpoints, the breakpoint is 0. > > The method then can be picked up by a compiler thread since > `number_of_breakpoints` is now 0 and a counter is real it falsely passes > `Method::is_not_compilable`. Then it copies the bytecode containing the > `breakpoint` instruction, and doesn't invoke the clean function since the > breakpoint count reports '0'. This causes a crash in the `ciBytecodeStream` > since `ciBytecodeStream::next_wide_or_table` assumes the only special > bytecodes can be `wide` or a type of switch, and bytecode is a special length > instruction. > > This also explains why this happens so rarely. For this to happen the > following need to happen in succession: > - The debugger must try to set breakpoints > - The method must never have been run > - Metadata space needs to be at the limit and not resized when its setting > the breakpoints and set the oom flag > - Class unloading must purge the flag afterwards > - The method must get compiled hot while the breakpoint is still installed > > 3 of the 5 conditions already happen when debugging with jdwp normally, from > platforms like intellij, the others are race / resource conditions that seem > happen very rarely. > > For the fix i propose to check the method counter allocation before actually > requesting a breakpoint set. Here done by checking if method counters are not > null before sending the vm request. I also had to expand the user facing > method to make sure the OOM error code is propagated properly (JVMTI_... Nice. ------------- PR Comment: https://git.openjdk.org/jdk/pull/33191#issuecomment-5984401960
