On Wed, 4 Feb 2026 07:19:03 GMT, Thomas Stuefe <[email protected]> wrote:
> Still Draft, pls ignore for now. Patch is not done yet. > > This patch enables hs-err file generation for native out-of-stack cases. It > is an optional analysis feature one can use when JVMs mysteriously vanish - > typically, vanishing JVMs are either native stack overflows or OOM kills. > > This was motivated by the analysis difficulties of bugs like > https://bugs.openjdk.org/browse/JDK-8371630. There are many more examples. > > ### Motivation > > Today, when native stack overflows, the JVM dies immediately without an > hs-err file. This is because C++-compiled code does not bang - if the stack > is too small, we walk right into whatever caps the stack. That might be our > own yellow/red guard pages, native guard pages placed by libc or kernel, or > possibly unmapped area after the end of the stack. > > Since we don't have a stack left to run the signal handler on, we cannot > produce the hs-err file. If one is very lucky, the libc writes a short "Stack > overflow" to stderr. But usually not: if it is a JavaThread and we run into > our own yellow/red pages, it counts as a simple segmentation fault from the > OS's point of view, since the fault address is inside of what it thinks is a > valid pthread stack. So, typically, you just see "Segmentation fault" on > stderr. > > ***Why do we need this patch? Don't we bang enough space for native code we > call?*** > > We bang when entering a native function from Java. The maximum stack size we > assume at that time might not be enough; moreover, the native code may be > buggy or just too deeply or infinitely recursive. > > ***We could just increase `ShadowPages`, right?*** > > Sure, but the point is we have no hs-err file, so we don't even know it was a > stack overflow. One would have to start debugging, which is work-intensive > and may not even be possible in a customer scenario. And for buggy recursive > code, any `ShadowPages` value might be too small. The code would need to be > fixed. > > ### Implementation > > The patch uses alternative signal stacks. That is a simple, robust solution > with few moving parts. It works out of the box for all cases: > - Stack overflows inside native JNI code from Java > - Stack overflows inside Hotspot-internal JavaThread children (e.g. > CompilerThread, AttachListenerThread etc) > - Stack overflows in non-Java threads (e.g. VMThread, ConcurrentGCThread) > - Stack overflows in outside threads that are attached to the JVM, e.g. > third-party JVMTI threads > > The drawback of this simplicity is that it is not suitable for always-on > production use. That is du... This also seems to break the SA core dump analysis when used. The main thread (that triggers the crash for core dump analysis) gives: sun.jvm.hotspot.debugger.DebuggerException: get_thread_regs failed for a lwp at jdk.hotspot.agent/sun.jvm.hotspot.debugger.bsd.BsdDebuggerLocal.getThreadIntegerRegisterSet0(Native Method) at jdk.hotspot.agent/sun.jvm.hotspot.debugger.bsd.BsdDebuggerLocal.getThreadIntegerRegisterSet(BsdDebuggerLocal.java:472) at jdk.hotspot.agent/sun.jvm.hotspot.debugger.bsd.BsdThread.getContext(BsdThread.java:68) at jdk.hotspot.agent/sun.jvm.hotspot.debugger.bsd.BsdCDebugger.topFrameForThread(BsdCDebugger.java:88) at jdk.hotspot.agent/sun.jvm.hotspot.tools.PStack.run(PStack.java:103) And if we do trigger a crash whilst on the alt-stack, we can't report it properly: # # A fatal error has been detected by the Java Runtime Environment: # # Internal Error (/System/Volumes/Data/mesos/work_dir/slaves/da1065b5-7b94-4f0d-85e9-a3a252b9a32e-S104193/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/c9064ba7-6869-444d-8711-6d351e4aef68/runs/13a2783a-fcf1-4587-9b41-fa976ba25ed0/workspace/open/src/hotspot/share/runtime/thread.hpp:469), pid=61163, tid=25603 # assert(stack_base() > limit && limit >= stack_end()) failed: limit is outside of stack # ... --------------- T H R E A D --------------- Current thread (0x000000013d057e10): [error occurred during error reporting (printing current thread), id 0xe0000000, Internal Error (/System/Volumes/Data/mesos/work_dir/slaves/da1065b5-7b94-4f0d-85e9-a3a252b9a32e-S104193/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/c9064ba7-6869-444d-8711-6d351e4aef68/runs/13a2783a-fcf1-4587-9b41-fa976ba25ed0/workspace/open/src/hotspot/share/runtime/thread.hpp:469)] Stack: [0x000000016ce30000,0x000000016ceb3000], sp=0x0000000105d89920 **OUTSIDE STACK**. Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code) V [libjvm.dylib+0x1250500] VMError::report(outputStream*, bool)+0x1d1c (thread.hpp:469) Interestingly a few tests seem to fail only on macOS. ------------- PR Comment: https://git.openjdk.org/jdk/pull/29559#issuecomment-3982244026 PR Comment: https://git.openjdk.org/jdk/pull/29559#issuecomment-3982248264
