[OpenSmalltalk/opensmalltalk-vm] VM crash (probably wrong forward pointer calculation) (Issue #614) - Vm-dev

18 Feb 2022


      This I what I get in the VS2022 debugger. Of course, at the moment I do not understand the code there, but maybe hopefully Eliot can see something interesting in it.  I leave VS open and look tomorrow at the code, maybe I understand a bit of it :-)
Seems there is something wrong with the forward pointers. I assume the longAt(referent) fails? I guess it is a macro, but VS could not find the definition.
########## Code area - the --> line is failing with access violation ###########
/* begin literalCountOfMethodHeader: */
    assert((((header) & 7) == 1));
    numLiterals = ((header >> 3)) & AlternateHeaderNumLiteralsMask;
    numSlots = numLiterals + LiteralStart;
    l9:	/* end numStrongSlotsOf:format:ephemeronInactiveIf: */;
    for (i = 0; i < numSlots; i += 1) {
    	referent = longAt((referrer + BaseHeaderSize) + (((sqInt)((usqInt)(i) << (shiftForWord())))));
    	if ((!(referent & (tagMask())))) {
/* a forwarding pointer could be because of become: or scavenging. */
-->			if ((!((longAt(referent)) & ((classIndexMask()) - (isForwardedObjectClassIndexPun()))))) {
    			/* begin followForwarded: */
    			assert(isUnambiguouslyForwarder(referent));
    			/* begin fetchPointer:ofMaybeForwardedObject: */
    			referent1 = longAt((referent + BaseHeaderSize) + (0U << (shiftForWord())));
    			while (((!(referent1 & (tagMask()))))
    			 && ((!((longAt(referent1)) & ((classIndexMask()) - (isForwardedObjectClassIndexPun())))))) {
    				/* begin fetchPointer:ofMaybeForwardedObject: */
    				referent1 = longAt((referent1 + BaseHeaderSize) + (0U << (shiftForWord())));
    			}
    			referent = referent1;
########## Call stack ############
Squeak.exe!scavengeReferentsOf(__int64 referrer) Zeile 42680
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\src\spur64.cog\cointerp.c (42680)
Squeak.exe!scavengeRememberedSetStartingAt(__int64 n) Zeile 42760
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\src\spur64.cog\cointerp.c (42760)
Squeak.exe!scavengeLoop() Zeile 42542
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\src\spur64.cog\cointerp.c (42542)
Squeak.exe!doScavenge(__int64 tenuringCriterion) Zeile 47599
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\src\spur64.cog\cointerp.c (47599)
Squeak.exe!scavengingGCTenuringIf(__int64 tenuringCriterion) Zeile 57959
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\src\spur64.cog\cointerp.c (57959)
Squeak.exe!sufficientSpaceAfterGC(__int64 numBytes) Zeile 58691
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\src\spur64.cog\cointerp.c (58691)
Squeak.exe!checkForEventsMayContextSwitch(__int64 mayContextSwitch) Zeile 62762
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\src\spur64.cog\cointerp.c (62762)
Squeak.exe!handleStackOverflowOrEventAllowContextSwitch(__int64 mayContextSwitch) Zeile 66037
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\src\spur64.cog\cointerp.c (66037)
Squeak.exe!ceStackOverflow(__int64 contextSwitchIfNotNil) Zeile 15593
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\src\spur64.cog\cointerp.c (15593)
[Externer Code]
Squeak.exe!ioInitHeartbeat() Zeile 420
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\platforms\win32\vm\sqWin32Heartbeat.c (420)
Squeak.exe!interpret() Zeile 2875
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\src\spur64.cog\cointerp.c (2875)
Squeak.exe!sqMain(int argc, char * * argv) Zeile 1761
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\platforms\win32\vm\sqWin32Main.c (1761)
Squeak.exe!WinMain(HINSTANCE__ * hInst, HINSTANCE__ * hPrevInstance, char * lpCmdLine, int nCmdShow) Zeile 1851
    unter C:\Users\joerg\Persoenlich\Entwicklung\Squeak\vmssource\trunk\platforms\win32\vm\sqWin32Main.c (1851)
[Externer Code]
########## Locals ############
classFormat	662660168776	__int64
    	contextSize	72198296718755736	__int64
    	fmt	2	__int64
    	foundNewReferentOrIsWeakling	0	__int64
    	header	140698790658008	__int64
    	header1	140698758633160	__int64
    	i	37029628	__int64
    	newLocation	811789632	__int64
    	numLiterals	64	__int64
    	numSlots	167772160	__int64
    	numSlots1	255	unsigned __int64
    	numSlots2	167772160	unsigned __int64
    	objOop1	72057594139401638	__int64
    	referent	139599658561184	__int64
    	referent1	0	__int64
    	referrer	140700938141704	__int64
    	sp	72058702004626295	__int64
############## Second try ##################
I needed to restart it again, here are my new local values in debugger
classFormat	973468582328	__int64
    	contextSize	72198310804720808	__int64
    	fmt	2	__int64
    	foundNewReferentOrIsWeakling	0	__int64
    	header	140699864399832	__int64
    	header1	140698758633160	__int64
    	i	81749860	__int64
    	newLocation	2070121416	__int64
    	numLiterals	64	__int64
    	numSlots	335544320	__int64
    	numSlots1	255	unsigned __int64
    	numSlots2	335544320	unsigned __int64
    	objOop1	72057594296693111	__int64
    	referent	139620721982368	__int64
    	referent1	0	__int64
    	referrer	140711869546504	__int64
    	sp	72058702004626295	__int64
numSlots seems to me very wrong. If I do some calculations I get also not the same value that the debugger says me. Here is the code
numLiterals = ((header >> 3)) & AlternateHeaderNumLiteralsMask;
    numSlots = numLiterals + LiteralStart;
AlternateHeaderNumLiteralsMask seems to be 0x7fff
    LiteralStart seems to be 1
For me is:
numLiterals = ((140699864399832 >> 3)) & 0x7fff = 32763		—> does not match the debugger local, where is the 64 coming from
Seems to me somebody has overridden already the „header“ variable, which seems to be wrong. Could it be that some other thread is writing in the wrong memory area and override my values?
Jörg
##########  System Information ##############
Gerätename	timemachine
Prozessor	AMD Ryzen 9 3900X 12-Core Processor               3.80 GHz
Installierter RAM	32,0 GB
Geräte-ID	F6FA897B-DDB1-44D6-9BF3-8BD1110AA754
Produkt-ID	00326-10048-08575-AA867
Systemtyp	64-Bit-Betriebssystem, x64-basierter Prozessor
Stift- und Toucheingabe	Für diese Anzeige ist keine Stift- oder Toucheingabe verfügbar.
Edition	Windows 10 Home
Version	20H2
Installiert am	‎23.‎03.‎2021
Betriebssystembuild	19042.1526
Leistung	Windows Feature Experience Pack 120.2212.4170.0
Visual Studio 2022
win64x64\squeak.cog.spur
VM version ???   I ask Eliot how i can see that on my current local github clone and post it later
############# Code for reproducation ##############
Simply execute the following Smalltalk code. Maybe you need to run it multiple times, for me the crash happens sometimes at the 3rd or 4th try.
| oc |
oc := OrderedCollection new.
400000000 timesRepeat: [oc add: Object new]
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