On 18.04.2016 12:53, Alexandre Julliard wrote:
Yes, MSYS2/Cygwin will switch to its own stack and deallocate the old one. This patch alone is not sufficient because there are still a couple of other references to the old stack (like the debug_info struct in start_thread).
If preferred, this issue can also be solved differently by calculting exit_frame dynamically based on StackBase (after a couple of other bugs are fixed). Disadvantage is that if applications mess around with StackBase, I'm not sure if we should trust that the new stack is set up properly.
The reason for exit_frame is to prevent pthread_exit from trying to unwind the stack. I'm wondering how that will work if it was deallocated. Did you look into this? Does pthread detect that we are on a different stack? And doesn't pthread also put its own structures on the stack?
Some versions of pthread indeed put internal structures at the top of the stack. To solve that, the current Staging patchset allocates threads with a dummy pthread, and then switches to the real stack, see: https://github.com/wine-compholio/wine-staging/blob/master/patches/ntdll-Thr... Unless there is something weird going on, thanks to the CFI annotations in wine_switch_to_stack() pthread should be able to unwind the stack correctly despite the stack switch inbetween. At least I have not found any problems so far ;)
You are right that ignoring exit_frame might (under specific circumstances) run language handlers, but I'm not yet aware of a better way to deal with this. The only alternative would be to calculate it based on StackBase, but its also far from perfect.