[Vm-dev] Difficult to debug VM crash with full blocks and Sista V1
Eliot Miranda
eliot.miranda at gmail.com
Sun Sep 29 23:27:58 UTC 2019
Hi Nicolas,
On Wed, Sep 25, 2019 at 12:32 AM Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> wrote:
>
> I noticed that many crash happen in testSendTimeout.
> This test is organizing a race:
> - Smalltalk fill the socket send buffer
> - the OS tries to drain
>
> The other thing I noticed is that [SocketTest suite run] takes 7 to 8s on
> macos while only 2 to 3s on ubuntu and windows
> So it might be that some test times out on macos, while it doesn't on
> other OS.
>
> This would explain that many crash also happen in JITted Timer loop, and
> that we cannot observe it in other OSes.
>
Yes, that is, I think, an important clue. The other one is that, given
that the crash always happens only early in a run, plus the address at
which it crashes in machine code, suggests to me that the crash occurs when
the interpreter invokes a block in the JITted startTimerLoop.
What worries me is that the JITted code for startTimerLoop looks completely
corrupted, not merely moved or overwritten (the method header looks OK up
to the selector field, which is the last field in the header). So I'm
wondering whether it could be a bug in support code overwriting machine
code, and hence that not might be related to a 32-bit vs 64-bit code
issue. I was hoping your recent sqUnixSocket.c changes might work but I'm
sure they have no bearing.
The access to OS ressources and the race may also explain some
> randomization of the crash...
>
> So one idea would be to make the test timeout in linux too, see if we can
> make it crash then try using rr.
> Maybe it's possible with a huge Socket buffer, a smaller image side buffer
> (we could reduce the size from 1000 to 1 so as to increase overhead).
>
Yes, that's a good idea. But I do think we need to set up a reliable
remote server, som thing that acts like an infinite sink for receiving a
par4ticular large Monticello package, so that ev very time the example runs
the same package is indeed copied to a remote server. Would it be possible
to construct such a fake Monticello server?
What I'm wanting the server to do is
a) take a while to respond to the Monticello package contents request
b) to never include a particular package which the example would always try
and upload
The test case would be to copy a particular version of VMMaker from
package-cache to the remote "fake" server
>
> It's just theories I tried to construct while biking, not in front of a
> keyboard, and I won't be able to verify until this evening...
> But the watchpoint strategy is too much vain shooting in the dark, we need
> more ellaborated plans ;)
>
Does anyone see the crash on macOS in 32 bits?
Le mar. 24 sept. 2019 à 00:28, Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com> a écrit :
>
>>
>>
>> Le mar. 24 sept. 2019 à 00:25, Nicolas Cellier <
>> nicolas.cellier.aka.nice at gmail.com> a écrit :
>>
>>> Follow up: so we have a problem of repeatability...
>>> I found nothing like rr for macos, and CPU watchpoint capability is too
>>> restricted to be usefull.
>>>
>>> So what I did is save a crash.image attempting to crash at resumption
>>> time:
>>> Smalltalk saveAs: 'crash'.
>>> Smalltalk snapshot: true andQuit: true.
>>> 5 timesRepeat: [SocketTest suite run].
>>>
>>> Then I launched the vm under lldb and gathered $pc stats to see if I
>>> could observe some reproducibility
>>> (lldb) p/x $pc - methodZoneBase
>>> 0x00000000000a0e94
>>> 0x0000000000090f70
>>> 0x000000000009f824
>>> 0x000000000009bfc8
>>> 0x000000000009d030
>>> 0x000000000009c7c0
>>> 0x00000000000951e0
>>> 0x00000000000949c8 <- once
>>> 0x0000000000094418
>>> 0x00000000000949c8 <— twice
>>> 0x000000000009b848
>>> 0x00000000000a0e94 <- twice
>>> 0x000000000009a176
>>> 0x000000006dfff2e0 ???
>>> 0x00000000000996d1
>>> 0x00000000000949c8 <- thrice good candidate for watchpoint set
>>> 0x000000000009ae70
>>> 0x000000000009ae70
>>> 0x00000000000a18e7
>>> 0x0000000000095470
>>> 0x000000000009c458
>>> 0x00000000000a0a7c
>>> 0x0000000000093e89
>>> 0x000000000009beb0
>>> 0x0000000000095a37
>>> 0x0000000000095408
>>> 0x00000000000a06bc
>>> 0x000000000009cd48
>>> 0x0000000000095408 <- twice
>>> 0x000000000009ba41
>>> 0x0000000000095408 <- thrice new candidate for watchpoint set
>>> 0x0000000000045258 <— smallest ever
>>> 0x000000000009c7c0
>>> 0x0000000000095408 <- fourth ! the watch point was set here, why didn’t
>>> it stop??? argh methodZoneBase was incremented after I set the watchpoint!!!
>>> 0x00000000000a12dc
>>> 0x00000000000951e0
>>> 0x00000000000a0e24
>>> 0x000000000009ff8c
>>> 0x000000000009c7f6
>>> 0x000000000009a626
>>>
>>> Then I have chosen to watch the most frequent crash address,
>>> that is methodZoneBase+0x0000000000095408,
>>> Unfortunately, s commented above, I missed one (I set the watchpoint too
>>> early, before methodZoneBase took its definitive address).
>>>
>>> And after a few (a bunch of) trials, here is what I found:
>>>
>>> (lldb) run ../../image/crash.image
>>> There is a running process, kill it and restart?: [Y/n]
>>> Process 28175 exited with status = 9 (0x00000009)
>>> Process 28185 launched:
>>> '/Users/nicolas/Smalltalk/OpenSmalltalk/opensmalltalk-vm/build.macos64x64/squeak.cog.spur/Squeak.app/Contents/MacOS/Squeak'
>>> (x86_64)
>>> Squeak was compiled with optimization - stepping may behave oddly;
>>> variables may not be available.
>>> Process 28185 stopped
>>> * thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint
>>> 6.1
>>> frame #0: 0x000000010007bc22 Squeak`-[sqSqueakOSXApplication
>>> doHeadlessSetup](self=0x000000010066fc00, _cmd="doHeadlessSetup") at
>>> sqSqueakOSXApplication.m:125 [opt]
>>> 122 //No super call here as we've already set headless from command
>>> line or info.plist
>>> 123 extern BOOL gSqueakHeadless;
>>> 124 // Notice that setActivationPolicy: is available in OSX 10.6
>>> and later
>>> -> 125 if ([NSApp respondsToSelector:@selector(setActivationPolicy:)])
>>> {
>>> 126 if (gSqueakHeadless) {
>>> 127 [NSApp
>>> setActivationPolicy:NSApplicationActivationPolicyProhibited];
>>> 128 } else {
>>> Target 0: (Squeak) stopped.
>>> (lldb) wa s e -s 1 -- methodZoneBase+0x0000000000095408
>>> Watchpoint created: Watchpoint 33: addr = 0x107c58138 size = 1 state =
>>> enabled type = w
>>> new value: -3689348814741910324
>>> (lldb) cont
>>> Process 28185 resuming
>>>
>>> Watchpoint 33 hit:
>>> old value: -3689348814741910324
>>> new value: -3689348814741910836
>>> Process 28185 stopped
>>> * thread #1, queue = 'com.apple.main-thread', stop reason = watchpoint 33
>>> frame #0: 0x00000001000731dc
>>> Squeak`fillInMethodHeadersizeselector(method=0x0000000107c58130, size=544,
>>> selector=4435118304) at cogitX64SysV.c:6320 [opt]
>>> 6317 sqInt rawHeader;
>>> 6318
>>> 6319 (method->cmType = CMMethod);
>>> -> 6320 (method->objectHeader = nullHeaderForMachineCodeMethod());
>>> 6321 (method->blockSize = size);
>>> 6322 (method->methodObject = methodObj);
>>> 6323
>>> Target 0: (Squeak) stopped.
>>> (lldb)
>>> Process 28185 resuming
>>>
>>> Watchpoint 33 hit:
>>> old value: -3689348814741910836
>>> new value: -3689571654825360894
>>> Process 28185 stopped
>>> * thread #1, queue = 'com.apple.main-thread', stop reason = watchpoint 33
>>> frame #0: 0x0000000100073255
>>> Squeak`fillInMethodHeadersizeselector(method=0x0000000107c58130, size=544,
>>> selector=4435118304) at cogitX64SysV.c:6339 [opt]
>>> 6336 (method->selector = selector);
>>> 6337 (method->cmNumArgs = argumentCountOfMethodHeader(methodHeader));
>>> 6338 (method->cmHasMovableLiteral = hasMovableLiteral);
>>> -> 6339 if ((method->cmRefersToYoung = hasYoungReferent)) {
>>> 6340 addToYoungReferrers(method);
>>> 6341 }
>>> 6342 (method->cmUsageCount = initialMethodUsageCount());
>>> Target 0: (Squeak) stopped.
>>> (lldb) bt
>>> * thread #1, queue = 'com.apple.main-thread', stop reason = watchpoint 33
>>> * frame #0: 0x0000000100073255
>>> Squeak`fillInMethodHeadersizeselector(method=0x0000000107c58130, size=544,
>>> selector=4435118304) at cogitX64SysV.c:6339 [opt]
>>> frame #1: 0x000000010004f90c Squeak`compileCogMethod [inlined]
>>> generateCogMethod(selector=<unavailable>) at cogitX64SysV.c:7098 [opt]
>>> frame #2: 0x000000010004f7a5
>>> Squeak`compileCogMethod(selector=4435118304) at cogitX64SysV.c:27780 [opt]
>>> frame #3: 0x000000010004bc54
>>> Squeak`cogselector(aMethodObj=4468481712, aSelectorOop=4435118304) at
>>> cogitX64SysV.c:4833 [opt]
>>> frame #4: 0x0000000100013d4d Squeak`primitiveClosureValue at
>>> gcc3x-cointerp.c:27237 [opt]
>>> frame #5: 0x0000000107bd1925
>>> frame #6: 0x000000010000236b Squeak`interpret at
>>> gcc3x-cointerp.c:2767 [opt]
>>> frame #7: 0x000000010008ed55 Squeak`-[sqSqueakMainApplication
>>> runSqueak](self=0x000000010066fc00, _cmd=<unavailable>) at
>>> sqSqueakMainApplication.m:201 [opt]
>>> frame #8: 0x00007fff44b077b8 Foundation`__NSFirePerformWithOrder +
>>> 360
>>> frame #9: 0x00007fff4297cf57
>>> CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__
>>> + 23
>>> frame #10: 0x00007fff4297ce7f CoreFoundation`__CFRunLoopDoObservers
>>> + 527
>>> frame #11: 0x00007fff4295f3f8 CoreFoundation`__CFRunLoopRun + 1240
>>> frame #12: 0x00007fff4295ec93 CoreFoundation`CFRunLoopRunSpecific +
>>> 483
>>> frame #13: 0x00007fff41c49d96 HIToolbox`RunCurrentEventLoopInMode +
>>> 286
>>> frame #14: 0x00007fff41c49a0f HIToolbox`ReceiveNextEventCommon + 366
>>> frame #15: 0x00007fff41c49884
>>> HIToolbox`_BlockUntilNextEventMatchingListInModeWithFilter + 64
>>> frame #16: 0x00007fff3fef9a73 AppKit`_DPSNextEvent + 2085
>>> frame #17: 0x00007fff4068fe34 AppKit`-[NSApplication(NSEvent)
>>> _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 3044
>>> frame #18: 0x00007fff3feee885 AppKit`-[NSApplication run] + 764
>>> frame #19: 0x00007fff3febda72 AppKit`NSApplicationMain + 804
>>> frame #20: 0x00007fff6a88c015 libdyld.dylib`start + 1
>>> (lldb)
>>>
>>> Here I don't know how to proceed, because I have no knowledge of this
>>> part of the VM, it's also quite late now...
>>> Eliot, does it ring some bell?
>>>
>>>
>> Ah, forget it, I thought it was overwriting, but it is the first write on
>> yet virgin methodeZone...
>> (it's just that the scenario was different from all the previous run)
>>
>> Le dim. 22 sept. 2019 à 11:21, Jan Vrany <jan.vrany at fit.cvut.cz> a
>>> écrit :
>>>
>>>>
>>>> On 2019-09-22 10:57, Nicolas Cellier wrote:
>>>> > Hi Jan,
>>>> > Thanks, a recording debugger would indeed be a tremendous help!
>>>> > Unfortunately, I'm unable to reproduce the bug under linux, only
>>>> > macosx...
>>>> > Do you know something equivalent to rr for mac?
>>>>
>>>> No, I don't. There might be something though, I never had a mac...
>>>>
>>>> Jan
>>>>
>>>> >
>>>> > Le dim. 22 sept. 2019 à 09:55, Jan Vrany <jan.vrany at fit.cvut.cz> a
>>>> > écrit :
>>>> >
>>>> >> Hi,
>>>> >>
>>>> >>>
>>>> >>> - can anyone think of any other strategies I might take to try and
>>>> >>> reproduce this?
>>>> >>>
>>>> >> at the risk of stating the obvious, in cases similar to this rr (+
>>>> >> VDB)
>>>> >> helped
>>>> >> me many times. See https://www.youtube.com/watch?v=Qbu4ED8wPYE
>>>> >>
>>>> >> Never used with opensmalltalk VM, though.
>>>> >>
>>>> >> HTH, Jan
>>>>
>>>
--
_,,,^..^,,,_
best, Eliot
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