* cygtls.cc (_cygtls::init_exception_handler): Fix comment.

	* cygtls.cc (_cygtls::handle_threadlist_exception): Make it clear that
	the function never actually returns.
	* exceptions.cc (_cygtls::handle_exceptions): Jump out of function
	rather than returning to avoid meddling by previously installed
	exception handlers.

3 files changed, 31 insertions, 10 deletions

diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 23268473026..ca3a0cf4a9f 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,15 @@
+2008-02-27  Corinna Vinschen  <corinna@vinschen.de>
+
+	* cygtls.cc (_cygtls::init_exception_handler): Fix comment.
+
+2008-02-27  Christopher Faylor  <me+cygwin@cgf.cx>
+
+	* cygtls.cc (_cygtls::handle_threadlist_exception): Make it clear that
+	the function never actually returns.
+	* exceptions.cc (_cygtls::handle_exceptions): Jump out of function
+	rather than returning to avoid meddling by previously installed
+	exception handlers.
+
 2008-02-21  Christopher Faylor  <me+cygwin@cgf.cx>
 
 	* dtable.cc (dtable::init_std_file_from_handle): Try harder to make a
diff --git a/winsup/cygwin/cygtls.cc b/winsup/cygwin/cygtls.cc
index 0b37ed6b379..c2d7c2ed72e 100644
--- a/winsup/cygwin/cygtls.cc
+++ b/winsup/cygwin/cygtls.cc
@@ -222,7 +222,7 @@ _cygtls::set_siginfo (sigpacket *pack)
   infodata = pack->si;
 }
 
-extern "C" DWORD __stdcall RtlUnwind (void *, void *, void *, DWORD);
+extern "C" DWORD __stdcall RtlUnwind (void *, void *, void *, DWORD) __attribute__ ((noreturn));
 int
 _cygtls::handle_threadlist_exception (EXCEPTION_RECORD *e, exception_list *frame, CONTEXT *c, void *)
 {
@@ -249,7 +249,7 @@ _cygtls::handle_threadlist_exception (EXCEPTION_RECORD *e, exception_list *frame
   cygheap->threadlist[threadlist_ix]->remove (INFINITE);
   threadlist_ix = 0;
   RtlUnwind (frame, threadlist_exception_return, e, 0);
-  return 0;
+  /* Never returns */
 }
 
 /* Set up the exception handler for the current thread.  The x86 uses segment
@@ -270,13 +270,8 @@ _cygtls::init_exception_handler (exception_handler *eh)
      At one point this was a loop (el.prev = &el;).  This outsmarted the
      above behaviour.  Unfortunately this trick doesn't work anymore with
      Windows 2008, which irremediably gets into an endless loop, taking 100%
-     CPU.  That's why we reverted to a normal SEH chain.
-
-     On the bright side, Windows' behaviour is covered by POSIX:
-
-     "If and when the function returns, if the value of sig was SIGFPE,
-     SIGILL, or SIGSEGV or any other implementation-defined value
-     corresponding to a computational exception, the behavior is undefined." */
+     CPU.  That's why we reverted to a normal SEH chain and changed the way
+     the exception handler returns to the application. */
   el.prev = _except_list;
   _except_list = &el;
 }
diff --git a/winsup/cygwin/exceptions.cc b/winsup/cygwin/exceptions.cc
index ad0af387166..2c9e0cb645f 100644
--- a/winsup/cygwin/exceptions.cc
+++ b/winsup/cygwin/exceptions.cc
@@ -664,7 +664,21 @@ _cygtls::handle_exceptions (EXCEPTION_RECORD *e, exception_list *frame, CONTEXT
   sig_send (NULL, si, &me);	// Signal myself
   me.incyg--;
   e->ExceptionFlags = 0;
-  return 0;
+  /* The OS adds an exception list frame to the stack.  It expects to be
+     able to remove this entry after the exception handler returned.
+     However, when unwinding to our frame, our frame becomes the uppermost
+     frame on the stack (%fs:0 points to frame).  This way, our frame
+     is removed from the exception stack and just disappears.  So, we can't
+     just return here or things will be screwed up by the helpful function
+     in (presumably) ntdll.dll.
+
+     So, instead, we will do the equivalent of a longjmp here and return
+     to the caller without visiting any of the helpful code installed prior
+     to this function.  This should work ok, since a longjmp() out of here has
+     to work if linux signal semantics are to be maintained. */
+
+  SetThreadContext (GetCurrentThread (), in);
+  return 0; /* Never actually returns.  This is just to keep gcc happy. */
 }
 
 /* Utilities to call a user supplied exception handler.  */