arch_setup_signal_frame(): panic() if we don't have a user iframe.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@26808 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/arch/x86/arch_thread.cpp

@@ -439,6 +439,11 @@ arch_setup_signal_frame(struct thread *thread, struct sigaction *action,
 	int signal, int signalMask)
 {
 	struct iframe *frame = get_current_iframe();
+	if (!IFRAME_IS_USER(frame)) {
+		panic("arch_setup_signal_frame(): No user iframe!");
+		return B_BAD_VALUE;
+	}
+
 	uint32 *signalCode;
 	uint32 *userRegs;
 	struct vregs regs;