<p>Hi Eliot,</p>
<p>Tracing back from the first time a warning is printed in the assert VM, it looks like what is happening is that a <code>BlockClosure</code> in the currently executing context is being moved during garbage collection, but that the FP isn't being updated.</p>
<p>I have a script which walks gdb to the point where the FP corruption occurs, but ignoring the multiple steps it takes to get to the correct iteration:</p>
<p>Setting a breakpoint in <code>scavengeReferentsOf()</code> at line 42259 in <code>gcc3x-cointerp.c</code> and then:</p>
<pre><code>(gdb) list
42254                                   if (oopisGreaterThanOrEqualToandLessThan(referent, ((futureSpace()).start), futureSurvivorStart())) {
42255                                           newLocation = referent;
42256                                           foundNewReferentOrIsWeakling = 1;
42257                                   }
42258                                   else {
42259                                           newLocation = copyAndForward(referent);
42260                                           if (((newLocation & (tagMask())) == 0)
42261                                            && (oopisLessThan(newLocation, GIV(newSpaceLimit)))) {
42262                                                   foundNewReferentOrIsWeakling = 1;
42263                                           }
(gdb) call printCallStack()
    0x7ffffffe3f70 I SessionManager>launchSnapshot:andQuit: 0x1508860: a(n) SessionManager
    0x7ffffffe3fe0 I [] in SessionManager>snapshot:andQuit: 0x1508860: a(n) SessionManager
    0x7ffffffe4020 I [] in BlockClosure>newProcess 0x118a728: a(n) BlockClosure

(gdb) n
(gdb) call printCallStack()
    0x7ffffffe3f70 I SessionManager>launchSnapshot:andQuit: 0x1508860: a(n) SessionManager
    0x7ffffffe3fe0 I [] in SessionManager>snapshot:andQuit: 0x1508860: a(n) SessionManager
    0x7ffffffe4020 I [] in INVALID RECEIVER>newProcess 0x118a728         0x118a728 is a forwarded object to          0x488fca0 of slot size 7 hdr8 .....
</code></pre>
<p>Setting a breakpoint at line 46909:</p>
<pre><code>(gdb) list
46904           /* begin initFutureSpaceStart */
46905           oldStart = GIV(futureSurvivorStart);
46906           GIV(futureSurvivorStart) = (GIV(futureSpace).start);
46907           GIV(pastSpaceStart) = oldStart;
46908           assert(oopisGreaterThanOrEqualToandLessThanOrEqualTo(GIV(pastSpaceStart), ((pastSpace()).start), ((pastSpace()).limit)));
46909           GIV(freeStart) = ((eden()).start);
46910           /* begin initSpaceForAllocationCheck:limit: */
46911           aNewSpace = (&(eden()));
46912           if (!(GIV(memory) == null)) {
46913                   if (checkAllocFiller()) {
(gdb) call printCallStack()
    0x7ffffffe3f70 I SessionManager>launchSnapshot:andQuit: 0x1508860: a(n) SessionManager
    0x7ffffffe3fe0 I [] in SessionManager>snapshot:andQuit: 0x1508860: a(n) SessionManager
    0x7ffffffe4020 I [] in INVALID RECEIVER>newProcess 0x118a728         0x118a728 is a forwarded object to          0x488fca0 of slot size 7 hdr8 .....
(gdb) n
46911           aNewSpace = (&(eden()));
(gdb) call printCallStack()
    0x7ffffffe3f70 I SessionManager>launchSnapshot:andQuit: 0x1508860: a(n) SessionManager
    0x7ffffffe3fe0 I [] in SessionManager>snapshot:andQuit: 0x1508860: a(n) SessionManager
    0x7ffffffe4020 I [] in INVALID RECEIVER>newProcess 0x118a728 is in new space
(gdb) 
</code></pre>
<p>The VM actually crashes some time later, however the call stack shows the an invalid receiver.</p>
<p>Shouldn't the FP be updated to point to the moved <code>BlockClosure</code>?</p>

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