[Vm-dev] Re: Cog Crash in allocateOpcodesbytecodes

Fri Apr 27 17:51:06 UTC 2012

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 ?

> 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
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