[Vm-dev] [OpenSmalltalk/opensmalltalk-vm] Reproduceable Segmentation fault while saving images (#444)

[Pavel Krivanek]

I tried to investigate the sensitivity of crashes probability on the eden
size and there is definitely some.
In my testing setup, if the eden size was set around 2 MB, it crashed.
For values around 1MB or 10 MB, there were no crashes or were significantly
less probable. However, there seems to be no strict limit.

-- Pavel

st 20. 11. 2019 v 12:59 odesílatel Alistair Grant <notifications at github.com>
napsal:

>
>
> Hi Eliot,
>
> Tracing back from the first time a warning is printed in the assert VM, it
> looks like what is happening is that a BlockClosure in the currently
> executing context is being moved during garbage collection, but that the FP
> isn't being updated.
>
> 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:
>
> Setting a breakpoint in scavengeReferentsOf() at line 42259 in
> gcc3x-cointerp.c and then:
>
> (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 .....
>
> Setting a breakpoint at line 46909:
>
> (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)
>
> The VM actually crashes some time later, however the call stack shows the
> an invalid receiver.
>
> Shouldn't the FP be updated to point to the moved BlockClosure?
>
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