Preliminary infrastructure to implement alternate stack

	* libc/include/sys/signal.h: Define SS_ONSTACK and SS_DISABLE
	unconditionally.
	(sigaltstack): Enable prototype on Cygwin.

	* common.din (sigaltstack): Export.
	* cygtls.cc (_cygtls::init_thread): Initialize altstack.
	* cygtls.h (__tlsstack_t): Rename from __stack_t to distinguish
	more clearly from stack_t.  Accommodate throughout.
	(_cygtls): Add altstack member.
	* exceptions.cc (exception::handle): Set SIGSEGV handler to SIG_DFL
	if we encounter a stack overflow, and no alternate stack has been
	defined.
	* include/cygwin/signal.h (MINSIGSTKSZ): Define
	(SIGSTKSZ): Define.
	(SA_ONSTACK): Define.
	* signal.cc (sigaltstack): New function.
	* tlsoffset.h: Regenerate.
	* tlsoffset64.h: Ditto.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

1 files changed, 39 insertions, 1 deletions

diff --git a/winsup/cygwin/signal.cc b/winsup/cygwin/signal.cc
index d2ca81e..7cb668c 100644
--- a/winsup/cygwin/signal.cc
+++ b/winsup/cygwin/signal.cc
@@ -587,7 +587,7 @@ sigwaitinfo (const sigset_t *set, siginfo_t *info)
 		*info = _my_tls.infodata;
 	      res = _my_tls.infodata.si_signo;
 	      _my_tls.sig = 0;
-	      if (_my_tls.retaddr () == (__stack_t) sigdelayed)
+	      if (_my_tls.retaddr () == (__tlsstack_t) sigdelayed)
 		_my_tls.pop ();
 	      _my_tls.unlock ();
 	    }
@@ -624,3 +624,41 @@ sigqueue (pid_t pid, int sig, const union sigval value)
   si.si_value = value;
   return sig_send (dest, si);
 }
+
+extern "C" int
+sigaltstack (const stack_t *ss, stack_t *oss)
+{
+  _cygtls& me = _my_tls;
+
+  if (ss)
+    {
+      if (me.altstack.ss_flags == SS_ONSTACK)
+	{
+	  set_errno (EPERM);
+	  return -1;
+	}
+      if (ss->ss_flags == SS_DISABLE)
+	{
+	  me.altstack.ss_sp = NULL;
+	  me.altstack.ss_flags = 0;
+	  me.altstack.ss_size = 0;
+	}
+      else
+	{
+	  if (ss->ss_flags)
+	    {
+	      set_errno (EINVAL);
+	      return -1;
+	    }
+	  if (ss->ss_size < MINSIGSTKSZ)
+	    {
+	      set_errno (ENOMEM);
+	      return -1;
+	    }
+	  memcpy (&me.altstack, ss, sizeof *ss);
+	}
+    }
+  if (oss)
+    memcpy (oss, &me.altstack, sizeof *oss);
+  return 0;
+}