Bizarre issue: For loop in DLL (witten in C) breaks early for no obvious reason

[Sebastian M. Ernst]

Hi everyone,

I'd like to draw you attention to an bizarre issue I am experiencing:
https://stackoverflow.com/q/49282888/1672565

Synopsis: I am experimenting with a DLL written in C and callback
functions written in Python. I am working with mingw (32 bit) on top of
64 bit Linux for compiling the DLL. For running the DLL and the Python
script, I am using an official 32 bit release build of CPython 3.5.3 for
Windows on top of 32 bit *Wine* 2.18. My DLL contains a for-loop, which
calls a call-back function in the Python script once per iteration. For
some really odd reason, the for loop breaks early after a fluctuating,
non-deterministic number of loops. The function containing the loop
continues to run as if nothing happened. For more details and code
examples please have a look at the question I posted as SO.

Apparently, my issue is not reproducible on Windows - at least comments
suggest that - so there is a chance that this is related to Wine. Thanks
for any help.

Best regards,
Sebastian

[Stefan Dösinger]

Hi,
> Am 14.03.2018 um 10:43 schrieb Sebastian M. Ernst :
>
> Hi everyone,
>
> I'd like to draw you attention to an bizarre issue I am experiencing:
> https://stackoverflow.com/q/49282888/1672565 https://stackoverflow.com/q/49282888/1672565

The calling convention mismatch that is explained in the comments sounds like a good guess to me because CDECL and STDCALL have different ideas on who cleans up the stack. The value of 'i' will be pushed to the stack before the call, but both conveyor_belt (because it is STDCALL) and the caller (because it thinks conveyor_belt is CDECL) will pop the call arguments, and eventually you'll pop something into i that is larger than len.