RFR: 8373128: Stack overflow handling for native stack overflows

[David Holmes]

On Wed, 4 Feb 2026 07:19:03 GMT, Thomas Stuefe <stuefe at openjdk.org> 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...

src/hotspot/share/code/nmethod.cpp line 943:

> 941:     // nmethod::continuation_for_implicit_exception runs in a signal handler, and
> 942:     // Method::print_codes_on implicitly assumes (see methodHandle::methodHandle)
> 943:     // that we run on the same stack as the faulting code.

I assume you are referring to:

// Constructor for metadata handles
#define DEF_METADATA_HANDLE_FN(name, type) \
inline name##Handle::name##Handle(Thread* thread, type* obj) : _value(obj), _thread(thread) { \
  if (obj != nullptr) {                                                   \
    assert(((Metadata*)obj)->is_valid(), "obj is valid");              \
    assert(_thread == Thread::current(), "thread must be current");    \
    assert(_thread->is_in_live_stack((address)this), "not on stack?"); \   <===== HERE
    _thread->metadata_handles()->push((Metadata*)obj);                 \
  }                                                                    \
}                                                                      \

but this code means we can't create any metadata handle whilst executing on the alt-stack. I triggered it by running the test `runtime/ErrorHandling/MachCodeFramesInErrorFile.java`. I'd suggest disabling the assert for UseAltSigStacks.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29559#discussion_r2870316016