On Tue, 19 May 2026 05:46:24 GMT, Thomas Stuefe <[email protected]> wrote:
>> 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 due t... > > Thomas Stuefe has updated the pull request with a new target base due to a > merge or a rebase. The incremental webrev excludes the unrelated changes > brought in by the merge/rebase. The pull request contains 26 additional > commits since the last revision: > > - Merge branch 'openjdk:master' into altsigstack > - fix runtime/ErrorHandling/ReattemptErrorTest.java > - fix windows build > - feedback yasumasa > - fix MachCodeFramesInErrorFile > - feedback david > - Update test/hotspot/jtreg/gtest/NativeStackOverflowGtest.java > > Co-authored-by: David Holmes > <[email protected]> > - fix gtests > - default-off > - reduce diff > - ... and 16 more: https://git.openjdk.org/jdk/compare/52d56e5e...e247a6cf not yet bot ------------- PR Comment: https://git.openjdk.org/jdk/pull/29559#issuecomment-4726069891
