Patch by Jan Klötzke (with additional TODO comments):

* Add a "fault_callback" to the thread structure which is called when a
  unhandled page fault happens in user space. A SIGSEGV will only be sent
  if the callback returns "true".


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25609 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/thread_types.h

@@ -224,6 +224,9 @@ struct team {
 
 typedef int32 (*thread_entry_func)(thread_func, void *);
 
+typedef bool (*page_fault_callback)(addr_t address, addr_t faultAddress,
+	bool isWrite);
+
 struct thread {
 	int32			flags;			// summary of events relevant in interrupt
 									// handlers (signals pending, user debugging
@@ -275,7 +278,13 @@ struct thread {
 		cbuf		*buffer;
 	} msg;
 
-	addr_t			fault_handler;
+	union {
+		addr_t		fault_handler;
+		page_fault_callback fault_callback;
+			// TODO: this is a temporary field used for the vm86 implementation
+			// and should be removed again when that one is moved into the
+			// kernel entirely.
+	};
 	int32			page_faults_allowed;
 		/* this field may only stay in debug builds in the future */
 

src/system/kernel/vm/vm.cpp

@@ -3864,8 +3864,13 @@ vm_page_fault(addr_t address, addr_t faultAddress, bool isWrite, bool isUser,
 			release_sem_etc(addressSpace->sem, READ_COUNT, 0);
 			vm_put_address_space(addressSpace);
 #endif
-			if (user_debug_exception_occurred(B_SEGMENT_VIOLATION, SIGSEGV))
+			struct thread *thread = thread_get_current_thread();
-				send_signal(team_get_current_team_id(), SIGSEGV);
+			// TODO: the fault_callback is a temporary solution for vm86
+			if (thread->fault_callback == NULL
+				|| thread->fault_callback(address, faultAddress, isWrite)) {
+				if (user_debug_exception_occurred(B_SEGMENT_VIOLATION, SIGSEGV))
+					send_signal(team_get_current_team_id(), SIGSEGV);
+			}
 		}
 	}