RFR: JDK-8257828: SafeFetch may crash if invoked in non-JavaThreads

[Thomas Stuefe]

In our primary hotspot signal handlers, SafeFetch handling is limited to JavaThread objects:

  JavaThread* thread = NULL;
...
  if(t->is_Java_thread()) {
    thread = (JavaThread*)t;
  }
...
  if (info != NULL && uc != NULL && thread != NULL) {
    pc = (address) os::Linux::ucontext_get_pc(uc);
    if (StubRoutines::is_safefetch_fault(pc)) {

As a result of this, using SafeFetch may crash non-JavaThreads if the location is invalid. E.g. using SafeFetch inside a VMOperation may crash the VM.

This is unfortunate since SafeFetch is used for os::is_readable_pointer() which explicitly promises to not crash. It is used e.g. in os::print_hex_dump(). There is also no reason why SafeFetch would not work for non-JavaThreads. In fact, SafeFetch handling for the secondary signal handler works just fine for all threads.

----

The patch makes handling of SafeFetch faults independent on whether the crashing thread is a JavaThread (indeed, whether we have a current Thread at all). This had been the case for AIX and Linux ppc, s390 before, since we already fixed this issue for our platform, so we know this works.

I also hauled the SafeFetch handling out of the platform dependent part of the signal handler into the generic signal handler. This removes some duplicate coding.

To be consistent, I moved the SafeFetch handling for Zero up into the generic signal handler too. Zero did not have a problem, but this reduces code.

I added a gtest which reproduces the issue and used that to check that the patch works.

Thanks, Thomas

-------------

Commit messages:
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/1695/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1695&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257828
  Stats: 170 lines in 11 files changed: 94 ins; 74 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1695.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1695/head:pull/1695

PR: https://git.openjdk.java.net/jdk/pull/1695