src/hotspot/os/posix/jvm_posix.cpp

/*
 * Copyright (c) 1999, 2025, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include "jvm.h"
#include "runtime/interfaceSupport.inline.hpp"
#include "runtime/osThread.hpp"
#include "signals_posix.hpp"

#include <signal.h>


// jdk.internal.misc.Signal ///////////////////////////////////////////////////////////

/*
 * This function is included primarily as a debugging aid. If Java is
 * running in a console window, then pressing <CTRL-\\> will cause
 * the current state of all active threads and monitors to be written
 * to the console window.
 */

JVM_ENTRY_NO_ENV(void*, JVM_RegisterSignal(jint sig, void* handler))
  void* newHandler = handler == (void *)2
                   ? PosixSignals::user_handler()
                   : handler;
  switch (sig) {
    /* The following are already used by the VM. */
    case SIGFPE:
    case SIGILL:
    case SIGSEGV:

#if defined(__APPLE__)
    /* On Darwin, memory access errors commonly results in SIGBUS instead
     * of SIGSEGV. */
    case SIGBUS:
#endif

    /* The following signal is used by the VM to dump thread stacks unless
       ReduceSignalUsage is set, in which case the user is allowed to set
       his own _native_ handler for this signal; thus, in either case,
       we do not allow JVM_RegisterSignal to change the handler. */
    case BREAK_SIGNAL:
      return (void *)-1;

    /* The following signals are used for Shutdown Hooks support. However, if
       ReduceSignalUsage (-Xrs) is set, Shutdown Hooks must be invoked via
       System.exit(), Java is not allowed to use these signals, and the
       user is allowed to set his own _native_ handler for these signals and
       invoke System.exit() as needed. Terminator.setup() is avoiding
       registration of these signals when -Xrs is present.
       - If the HUP signal is ignored (from the nohup) command, then Java
         is not allowed to use this signal.
     */

    case SHUTDOWN1_SIGNAL:
    case SHUTDOWN2_SIGNAL:
    case SHUTDOWN3_SIGNAL:
      if (ReduceSignalUsage) return (void*)-1;
      if (PosixSignals::is_sig_ignored(sig)) return (void*)1;
  }

  void* oldHandler = PosixSignals::install_generic_signal_handler(sig, newHandler);
  if (oldHandler == PosixSignals::user_handler()) {
      return (void *)2;
  } else {
      return oldHandler;
  }
JVM_END


JVM_ENTRY_NO_ENV(jboolean, JVM_RaiseSignal(jint sig))
  if (ReduceSignalUsage) {
    // do not allow SHUTDOWN1_SIGNAL,SHUTDOWN2_SIGNAL,SHUTDOWN3_SIGNAL,
    // BREAK_SIGNAL to be raised when ReduceSignalUsage is set, since
    // no handler for them is actually registered in JVM or via
    // JVM_RegisterSignal.
    if (sig == SHUTDOWN1_SIGNAL || sig == SHUTDOWN2_SIGNAL ||
        sig == SHUTDOWN3_SIGNAL || sig == BREAK_SIGNAL) {
      return JNI_FALSE;
    }
  }
  else if ((sig == SHUTDOWN1_SIGNAL || sig == SHUTDOWN2_SIGNAL ||
            sig == SHUTDOWN3_SIGNAL) && PosixSignals::is_sig_ignored(sig)) {
    // do not allow SHUTDOWN1_SIGNAL to be raised when SHUTDOWN1_SIGNAL
    // is ignored, since no handler for them is actually registered in JVM
    // or via JVM_RegisterSignal.
    // This also applies for SHUTDOWN2_SIGNAL and SHUTDOWN3_SIGNAL
    return JNI_FALSE;
  }

  ::raise(sig);
  return JNI_TRUE;
JVM_END