[Vm-dev] Difficult to debug VM crash with full blocks and Sista V1

[Phil B]

It sounds like simulating a terrible (dropping packets) or painfully slow
(kbps speeds) network connection might be a more controlled way to
reproduce the issue:
https://apple.stackexchange.com/questions/24066/how-to-simulate-slow-internet-connections-on-the-mac

On Fri, Sep 13, 2019 at 11:16 PM Eliot Miranda <eliot.miranda at gmail.com>
wrote:

>
> Hi All,
>
>     there is a VM bug in 64-bit Spur with the Sista V1 bytecode set and
> full blocks.  The symptom is that when waiting for a remote Monticello
> repository to update and/or deliver a package version the system crashes in
> JITTED code after what appears to be some kind of wait.
>
> This is a reliably occurring bug b ut maddeningly difficult to reproduce.
> The bug reliably occurs when interacting with a remote rep[ository (e.g.
> http://source.squeak.org/VMMaker) when the server is "cold", and hence
> makes the image wait.  Every time I have tried to repeat the failing
> sequence the crash has not occurre3d, I think because the server is now
> "hot" and serves up the version quickly.  Today I even tried shutting down
> my machine for over an hour and rebooting.  But I could not get the crash
> to occur even though it seems to me that every time I try it the first time
> in the4 day it does crash.
>
> This is an important bug to fix.  If it cannot be fixed then full blocks
> and Sista V1 are not ready for use in the upcoming Squeak release.  I am
> looking for help in debugging this.
>
> - is anyone else uising the 64-bit VM with full blocks and Sista V1 who
> sees hard VM crashes?  If so, under what circumstances?
>
> - is it possible to flush caches in the http://source.squeak.org/VMMaker
> server, or could people tolerate me rebooting the server?
>
> - is there a way of introducing network delays in Mac OS that might help
> me induce the bug?
>
> - can anyone think of any other strategies I might take to try and
> reproduce this?
>
> I may have to try and reproduce e the bug in the simulator to have a
> chance of identifying the bug.  Does anyone have a good enough mental model
> of the Monticello server interaction and have energy to help me figure this
> one out?
>
> Here is some information from the last crash I did see in the debugger
> (alas it is incomplete; there are a number of additional pieces of info I
> could have collected).
>
> (lldb) thr b
>
> * thread #1, queue = 'com.apple.main-thread', stop reason =
> EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
>
>   * frame #0: 0x000000010de5700a
>
>     frame #1: 0x000000010dd7b174
>
>     frame #2: 0x000000010dd45f1c
>
>     frame #3: 0x000000010dd44534
>
>     frame #4: 0x000000010dd44c60
>
> (lldb) x/10i 0x000000010de5700a
>
>
> (lldb) call printStackCallStackOf($rbp)
>
>     0x7ffeefbdfc30 M Heap>upHeap: 0x11273ca90: a(n) Heap
>
>     0x7ffeefbdfc68 M Heap>add: 0x11273ca90: a(n) Heap
>
>     0x7ffeefbdfca0 M Delay class>scheduleDelay:from: 0x1123ebfb8: a(n)
> Delay class
>
>     0x7ffeefbdfcf0 M Delay class>handleTimerEvent 0x1123ebfb8: a(n) Delay
> class
>
>     0x7ffeefbdfd20 M Delay class>runTimerEventLoop 0x1123ebfb8: a(n) Delay
> class
>
>
> (lldb) x/10i 0x000000010dd7b174
>
>     0x10dd7b174: 48 8b 55 10  movq   0x10(%rbp), %rdx
>
>     0x10dd7b178: 48 89 ec     movq   %rbp, %rsp
>
>     0x10dd7b17b: 5d           popq   %rbp
>
>     0x10dd7b17c: c2 10 00     retq   $0x10
>
>     0x10dd7b17f: cc           int3
>
>     0x10dd7b180: cc           int3
>
>     0x10dd7b181: cc           int3
>
>     0x10dd7b182: cc           int3
>
>     0x10dd7b183: cc           int3
>
>     0x10dd7b184: cc           int3
>
> (lldb) print whereIs(0x000000010dd7b174)
>
> (char *) $0 = 0x00000001000f83ff " is in generated methods"
>
> (lldb) call printCogMethodFor((void *)0x000000010dd7b174)
>
>        0x10dd7afc0 <->        0x10dd7b198: method:        0x112f23c10
> selector:        0x112232c20 add:
>
> (lldb) print whereIs(0x000000010de5700a)
>
> (char *) $1 = 0x00000001000f83ff " is in generated methods"
>
> (lldb) call printCogMethodFor((void *)0x000000010de5700a)
>
>        0x10de56ba0 <->        0x10de57078: method:        0x1126ec218 prim
> 23856 selector:     0x7ffeefbf3d20
>
> this method ends up being the fitted version of Delay class>>
>  startTimerEventLoop
> _,,,^..^,,,_
> best, Eliot
>
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