[Vm-dev] new Cog VMs available [please read]

Eliot Miranda eliot.miranda at gmail.com
Thu Sep 22 17:37:22 UTC 2011

...in http://www.mirandabanda.org/files/Cog/VM/VM.r2493/.  These VMs are not
much changed from the 2487 VMs, BUT the 2487 VMs introduced a bug while
providing faster doesNotUnderstand: processing.  These 2493 VMs contain code
to help identify that bug.  If you're already using a 2487 VM or newer
/please/ upgrade to these 2493 VMs asap.  I want to see C stack backtraces
from these VMs whenever they crash.  Typically the VMs produce a crash.dmp
file somewhere in the file system (may be / on Mac OS, may be in the
directory containing the VM or the current directory on other OSs, but it
will be called crash.dmp, and on Mac OS info will be printed to the console
or to a crash report window).  The C backtrace part of things looks like

this on windows:
Stack backtrace:
[004193EA] ??? + 4297706 in CogCode
[00442337] ??? + 4465463 in CogCode
[00442685] ??? + 4466309 in CogCode
[00583018] ??? + 5779480 in CogCode
[0040124B] ??? + 4198987 in CogCode
[00401298] ??? + 4199064 in CogCode
[7C816FE7] RegisterWaitForInputIdle + 73 in kernel32.dll
[7C913BA7] RtlDosApplyFileIsolationRedirection_Ustr + 1824 in ntdll.dll

this on Mac
C stack backtrace:
0   nsvm                                0x00038689 reportStackState + 105
1   nsvm                                0x0003893e sigsegv + 110
2   libsystem_c.dylib                   0x9b2e259b _sigtramp + 43
3   ???                                 0xffffffff 0x0 + 4294967295
4   nsvm                                0x0008b2a5 sufficientSpaceAfterGC +
5   nsvm                                0x0008d11d primitiveNewWithArg + 221
6   ???                                 0x068b9899 0x0 + 109811865
7   nsvm                                0x00098d10
initStackPagesAndInterpret + 512
8   nsvm                                0x0002c530 EventLoopEventHandler +

Etc.  So please feel free to email me the crash.dmp's and/or the C
backtraces of any crashes you have with 2493 VMs.  Hopefully I'll track down
this regression quickly.

For the curious, what's the bug?  I don't know yet. The symptom is that very
rarely the inline cache linking machinery for MNU PICs relinks the call of
an MNU PIC to the address 0x00000013, which causes a crash when the call is
next executed, long after the bug bit.  These VMs contain code that will
raise an error when the relinking attempt is made, which should reveal the

Here's the 2493 readme:

CogVM binaries as per VMMaker.oscog-eem.125/r2493.  Add callsite link/relocate
checks to catch the call 0x00000013 MNU callsite relinking bug.
Reduce the size of the simStack to something proportional to LargeContextSize.

In the Newspeak VM, don't cd to the image's directory on win32.  Fix off-by-one
error in Win32OSProcessPlugin>primitiveGetCurrentWorkingDirectory so it doesn't
include an erroneous trailing null.

Fix the 1Gb allocation bug.

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