[Vm-dev] Corrupt Stack When Trying To Simulate Cogged SmallInteger>>#+

Kruck, Bastian Bastian.Kruck at student.hpi.de
Thu Jan 19 10:09:46 UTC 2017

Hi Folks,

Do you have a moment to give me a hint on the following error?

I’m currently trying to get the result of the cogged version of SmallInteger>>#+ by simulating it in VMMaker. So I initialise the simulator, lookup the method in the loaded image and finally start Bochs by calling simulator activateCoggedNewMethod: false.

Now I can see the primitiveSingleStepInMemoryMinimumAddressReadWrite failing when trying trying to return to esp=16r11 which is my receiver. So it seems my stack gets corrupted at some point. So I start tracing what the processor is doing:

- starts at ceEnterCogCodePopReceiverReg (pc=16r1128)
- then it enters the compiled SmallInteger>>#+ (pc= 16r1462, the position with HasByteCodePC)
- then it enters ceSuperSend1Args (pc=16r570)
- and runs further up to the return (at pc=16r5aa) where it will have the esp=16r11

Can you give me a hint on what’s happening here? I put the notes while tracing into a txt file that you can find attached. If you want to try it out yourself, I uploaded the image and the VM version here https://www.dropbox.com/sh/6sevutlcpx3of42/AAA9ScgmvK5IeLaCxE6yWJ8Ua?dl=0

The Background: I’m currently working on my master thesis on Multi-Level Debugging where I’m building a debugger that is supposed to detect erroneous code transformations by redundantly executing the Slang, the running vm, the fallback code and also the JIT-compiled fallbacks.

Thank you so much!

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