[SystemZ] Support System Z as host architecture

The llvm::sys::AddSignalHandler function (as well as related routines) in
lib/Support/Unix/Signals.inc currently registers a signal handler routine
via "sigaction".  When this handler is called due to a SIGSEGV, SIGILL or
similar signal, it will show a stack backtrace, deactivate the handler,
and then simply return to the operating system.  The intent is that the
OS will now retry execution at the same location as before, which ought
to again trigger the same error condition and cause the same signal to be
delivered again.  Since the hander is now deactivated, the OS will take
its default action (usually, terminate the program and possibly create
a core dump).

However, this method doesn't work reliably on System Z:  With certain
signals (namely SIGILL, SIGFPE, and SIGTRAP), the program counter stored
by the kernel on the signal stack frame (which is the location where
execution will resume) is not the instruction that triggered the fault,
but then instruction *after it*.  When the LLVM signal handler simply
returns to the kernel, execution will then resume at *that* address,
which will not trigger the problem again, but simply go on and execute
potentially unrelated code leading to random errors afterwards.

To fix this, the patch simply goes and re-raises the signal in question
directly from the handler instead of returning from it.  This is done
only on System Z and only for those signals that have this particular
problem.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181010 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Support/Unix/Signals.inc b/lib/Support/Unix/Signals.inc
index fcb12e353401f06e3294dae3641ce05a6695e38a..64d1fc1c0807798ad653e251d2e00c29e8b5fe5f 100644 (file)
--- a/lib/Support/Unix/Signals.inc
+++ b/lib/Support/Unix/Signals.inc
@@ -186,6 +186,15 @@ static RETSIGTYPE SignalHandler(int Sig) {
   // Otherwise if it is a fault (like SEGV) run any handler.
   for (unsigned i = 0, e = CallBacksToRun.size(); i != e; ++i)
     CallBacksToRun[i].first(CallBacksToRun[i].second);
+
+#ifdef __s390__
+  // On S/390, certain signals are delivered with PSW Address pointing to
+  // *after* the faulting instruction.  Simply returning from the signal
+  // handler would continue execution after that point, instead of
+  // re-raising the signal.  Raise the signal manually in those cases.
+  if (Sig == SIGILL || Sig == SIGFPE || Sig == SIGTRAP)
+    raise(Sig);
+#endif
 }
 
 void llvm::sys::RunInterruptHandlers() {