[Vm-dev] Re: Cog Crash in allocateOpcodesbytecodes

Fri Apr 27 18:01:10 UTC 2012

On Fri, Apr 27, 2012 at 10:51 AM, Mariano Martinez Peck <
marianopeck at gmail.com> wrote:

>
>
>
> On Fri, Apr 27, 2012 at 7:34 PM, Eliot Miranda <eliot.miranda at gmail.com>wrote:
>
>>
>>
>>
>> On Fri, Apr 27, 2012 at 1:33 AM, Mariano Martinez Peck <
>> marianopeck at gmail.com> wrote:
>>
>>>
>>>
>>>
>>> On Fri, Apr 27, 2012 at 2:00 AM, Eliot Miranda <eliot.miranda at gmail.com>wrote:
>>>
>>>>
>>>>
>>>>
>>>> On Thu, Apr 26, 2012 at 3:26 PM, Mariano Martinez Peck <
>>>> marianopeck at gmail.com> wrote:
>>>>
>>>>>
>>>>>
>>>>>
>>>>>> On Thu, Apr 26, 2012 at 10:42 PM, Mariano Martinez Peck <
>>>>>> marianopeck at gmail.com> wrote:
>>>>>>
>>>>>>> Hi Eliot. We are doing a crazy experiment where we serialize almost
>>>>>>> all PharoCore and we materialize it in a PharoKernel image. During the
>>>>>>> initialization (after the load), there is one line that crashes Cog:
>>>>>>>
>>>>>>> PolymorphSystemSettings showDesktopLogo: true.
>>>>>>>
>>>>>>>
>>>>>
>>>>>> For what I can see, I may be related to the fact that
>>>>>>> #pharoLogoContents is too long or something like that?
>>>>>>>
>>>>>>
>>>>> hehehe now I remember we are putting the source code in the method
>>>>> trailer. And #pharoLogoContents is too much I guess:
>>>>>
>>>>> (PolymorphSystemSettings class >> #pharoLogoContents)  trailer size
>>>>> ->  49726
>>>>>
>>>>> so..is this a known limitation?
>>>>>
>>>>
>>>> It's been invisible until now :)
>>>>
>>>>
>>>>
>>>> Ah!  I see.  The JIT compilation process in Cog goes as follows (see
>>>> Cogit>compileCogMethod:).  Guess the endPC of the method based on its byte
>>>> size.  Stack allocate space for compilation based on this.  Make an initial
>>>> pass over the bytecode to a) initialize fixups for the targets of backward
>>>> jumps, b) count how many blocks the method contains, and c) determine the
>>>> method's real endPC.  Fixups are used to generate code for branches; they
>>>> point from the target instruction back to the jump(s) to this instruction.
>>>>  Since we scan forward we can create the fixups for forward branches when
>>>> we encounter the branch.  But backward jumps have to be done up front.
>>>>
>>>> So there's a chicken-and-egg problem.  The JIT either needs to guess
>>>> how many fixups it needs before it scans, or it needs to make an extra scan
>>>> of the bytecocde to determine the actual endPC before it scans to
>>>> initialize fixups.  I hate to add an extra pass unnecessarily.  So is there
>>>> a simple criterion the JIT can use to know whether it has to make an extra
>>>> pass?
>>>>
>>>>
>>> Hi Eliot. We thought about different possibilities but I think the
>>> easier is to just modify #methodWithHeaderShouldBeCogged: to reject methods
>>> "too long". So apart from checking the number of literals you can also
>>> check the total amount of bytes and be sure to be less that the amount that
>>> causes the crash in allocateOpcodesbytecodes. ?
>>>
>>> Another possibility is to add a word to CompiledMethod header that
>>> stores the endPC, so there is not need to guess. But we will need some
>>> image-changes and break comptatbilty.
>>>
>>
>> I think the right thing to do if for the JIT to do a scan to determine
>> the actual end pc
>>
>
> but how do you determinate the end pc ?
>

Scan the bytecodes.  See Cogit>scanMethod.

>
>
>
>>  if the method's byte codes are greater than some limit, e.g. 1024 bytes
>> of bytecodes.  It then rejects the method if the actual end pc is greater
>> than some limit that we find empirically causes the JIT to crash because of
>> the size of the alloca.
>>
>>
>>> Cheers
>>>
>>>
>>>
>>>
>>>
>>>>
>>>>
>>>>>
>>>>> thanks!
>>>>>
>>>>>
>>>>>>  the same experiment with StackVM works fine.
>>>>>>> Of course in a normal image (without this experiment) I can do
>>>>>>> PolymorphSystemSettings showDesktopLogo: true. without problems.
>>>>>>>
>>>>>>>
>>>>>>> From gdb i see:
>>>>>>>
>>>>>>> (gdb) bt
>>>>>>> #0  0x0000a190 in compileCogMethod (selector=528828260) at
>>>>>>> /Users/mariano/Pharo/VM/git/cogVMBlessedSSH/blessed/build/../src/vm/cogit.c:
>>>>>>> 3601
>>>>>>> #1  0x00009088 in cogselector (aMethodObj=531503072,
>>>>>>> aSelectorOop=528828260) at
>>>>>>> /Users/mariano/Pharo/VM/git/cogVMBlessedSSH/blessed/build/../src/vm/cogit.c:
>>>>>>> 3129
>>>>>>> #2  0x0003268b in ceSendsupertonumArgs (selector=528828260,
>>>>>>> superNormalBar=0, rcvr=536158520, numArgs=0) at
>>>>>>> /Users/mariano/Pharo/VM/git/cogVMBlessedSSH/blessed/build/../src/vm/gcc3x-cointerpmt.c:11007
>>>>>>> #3  0x1f40006c in ?? ()
>>>>>>> #4  0x00067350 in threadSchedulingLoop (vmThread=0x1030c00) at
>>>>>>> /Users/mariano/Pharo/VM/git/cogVMBlessedSSH/blessed/build/../src/vm/gcc3x-cointerpmt.c:44006
>>>>>>> #5  0x0003d2cb in initialEnterSmalltalkExecutive () at
>>>>>>> /Users/mariano/Pharo/VM/git/cogVMBlessedSSH/blessed/build/../src/vm/gcc3x-cointerpmt.c:17788
>>>>>>> #6  0x0003df8f in initStackPagesAndInterpret () at
>>>>>>> /Users/mariano/Pharo/VM/git/cogVMBlessedSSH/blessed/build/../src/vm/gcc3x-cointerpmt.c:18208
>>>>>>> #7  0x00022618 in interpret () at
>>>>>>> /Users/mariano/Pharo/VM/git/cogVMBlessedSSH/blessed/build/../src/vm/gcc3x-cointerpmt.c:2066
>>>>>>> #8  0x0006dc60 in -[sqSqueakMainApplication runSqueak]
>>>>>>> (self=0x1d0ca60, _cmd=0x124ebf) at
>>>>>>> /Users/mariano/Pharo/VM/git/cogVMBlessedSSH/blessed/build/../platforms/iOS/vm/Common/Classes/sqSqueakMainApplication.m:174
>>>>>>> #9  0x93ad586c in __NSFirePerformWithOrder ()
>>>>>>> #10 0x908b8dd2 in __CFRunLoopDoObservers ()
>>>>>>> #11 0x90874ced in __CFRunLoopRun ()
>>>>>>> #12 0x908743c4 in CFRunLoopRunSpecific ()
>>>>>>> #13 0x908741f1 in CFRunLoopRunInMode ()
>>>>>>> #14 0x97760e04 in RunCurrentEventLoopInMode ()
>>>>>>> #15 0x97760af5 in ReceiveNextEventCommon ()
>>>>>>> #16 0x97760a3e in BlockUntilNextEventMatchingListInMode ()
>>>>>>> #17 0x96d1a595 in _DPSNextEvent ()
>>>>>>> #18 0x96d19dd6 in -[NSApplication
>>>>>>> nextEventMatchingMask:untilDate:inMode:dequeue:] ()
>>>>>>> #19 0x96cdc1f3 in -[NSApplication run] ()
>>>>>>> #20 0x96cd4289 in NSApplicationMain ()
>>>>>>> #21 0x0006b9f9 in main (argc=1, argv=0xbffff688, envp=0xbffff690) at
>>>>>>> /Users/mariano/Pharo/VM/git/cogVMBlessedSSH/blessed/build/../platforms/iOS/vm/Common/main.m:52
>>>>>>>
>>>>>>>
>>>>>>> And the line that fails is:
>>>>>>> allocateOpcodesbytecodes((numBytecodes + extra) * 10, numBytecodes);
>>>>>>>
>>>>>>> numBytecodes is 49729 and extra is 10.
>>>>>>>
>>>>>>> Any idea?
>>>>>>>
>>>>>>> thanks!
>>>>>>>
>>>>>>> --
>>>>>>> Mariano
>>>>>>> http://marianopeck.wordpress.com
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Mariano
>>>>>> http://marianopeck.wordpress.com
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Mariano
>>>>> http://marianopeck.wordpress.com
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> best,
>>>> Eliot
>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>> Mariano
>>> http://marianopeck.wordpress.com
>>>
>>>
>>>
>>
>>
>> --
>> best,
>> Eliot
>>
>>
>>
>
>
> --
> Mariano
> http://marianopeck.wordpress.com
>
>
>

-- 
best,
Eliot
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