Re: [Valgrind-developers] drd 2006-12-30

[Duncan S. <bal...@fr...>]

On Tuesday 2 January 2007 13:59, Bart Van Assche wrote:
> On 1/1/07, Duncan Sands <bal...@fr...> wrote:
> > Hi Bart,
> >
> > > A new drd version is available at
> > > http://home.euphonynet.be/bvassche/valgrind/valgrind-6458-drd-2006-12-30.patch.gz.
> >
> > thanks for doing this.  I gave it a whirl and it seems to work fine.  However it
> > reported a false positive: two threads, thread 1 and thread 2, write to the same
> > memory location in an unsynchronized way, but they write *the same value* to it.
> > Thread 1 then reads the value, which may have last been written by thread 1 or
> > thread 2.  This gets reported as a race, even though there is no race since the
> > value read is independent of the order in which the threads wrote it:
> 
> It wouldn't be easy to recognize this pattern in the drd tool.

Drat.

> Is it 
> possible to generate a suppression pattern with Valgrind's option
> --gen-suppressions=all ? If it is the conflicting accesses are
> triggered by the Ada implementation, I can add them to the default drd
> suppression file.

It is indeed in the Ada implementation.  The following seems to work:

--- default.supp	2007-01-02 14:18:33.000000000 +0100
+++ /usr/local/lib/valgrind/drd/default.supp	2007-01-02 14:42:49.000000000 +0100
@@ -188,3 +188,10 @@
    drd:ConflictingAccess
    fun:_pthread_cleanup_push_defer
 }
+{
+   gnat@create_task
+   drd:ConflictingAccess
+   fun:system__task_primitives__operations__set_priority
+   fun:system__task_primitives__operations__create_task
+   fun:system__tasking__stages__activate_tasks
+}

Best wishes,

Duncan.