Changeset 12907

Timestamp:

Oct 4, 2009, 6:46:58 PM (15 years ago)

Author:

R. Matthew Emerson

Message:

Offer an "allow this write" restart in response to a
write-to-watched-object condition. There's a dangerous flaw here: if
another thread unwatches the object while we're in the handler,
unpleasantness is likely to ensue.

File:

• branches/watchpoints/level-1/x86-trap-support.lisp (modified) (2 diffs)

branches/watchpoints/level-1/x86-trap-support.lisp

@@ -432 +432 @@
              ((= code 2)
               ;; Write to a watched object.
+              ;; We somehow need to guard against another thread unwatching
+              ;; the object out from underneath us.
               (flet ((%int-to-object (i)
                        (rlet ((a :address))
@@ -445 +447 @@
                                            :object object)
                                           nil frame-ptr)
+                      ;; This certainly has the potential to cause amusing
+                      ;; errors.
+                      (allow ()
+                        :report "Allow this write."
+                        (let ((result nil)
+                              (ptr (%int-to-ptr
+                                    (logandc2 addr (1- *host-page-size*)))))
+                          (with-other-threads-suspended
+                            (#_mprotect ptr *host-page-size*
+                                        #$PROT_WRITE)
+                            (setq result (x86-emulate-write-instruction xp insn addr object))
+                            (#_mprotect ptr *host-page-size*
+                                        (logior #$PROT_READ #$PROT_EXEC)))
+                          (if result
+                            (setq skip insn-length)
+                            (error "can't emulate this write"))))
                       (ignore ()
                         :report "Ignore this write."