why procsupt.asm executes code on stack?

[stsp]

https://github.com/dosemu2/fdpp/blob/master/kernel/procsupt.asm#L187

@bartoldeman @ecm-pushbx
could you please hint me why
that code creates an on-stack
trampoline? Do other DOSes
have the same? Or should I
change it to plain code?

[ecm-pushbx]

I think this is probably an attempt to implement the retf vs retf 2 vs iret semantics of calling int 23h. However, it is incorrect in that the int 23h is supposed to run on the original int 21h stack, which is why lDOS put the int 23h caller into DOSDATA so that it can access DOS variables using cs: overrides: https://hg.pushbx.org/ecm/msdos4/file/fdd6a0a0fcac/src/DOS/ctrlc.nas#l313

The fact that int 23h runs with the int 21h stack frame isn't directly listed in the interrupt list: https://fd.lod.bz/rbil/interrup/dos_kernel/23.html#4153

[stsp]

Ok, done.
The interesting thing is that
once again I removed more
lines than added, so this is
actually simpler than running
on a DOS stack.

[ecm-pushbx]

Ok, better, but you still modify bp and push its old value to the stack: 4c349d8#diff-1194af90460449def6e5129526dad8e3008c0a36203dfe1bb56604478355d278L110

That's a smaller modification than the trampoline business but still not passing the exact sp and bp to the int 23h handler.

[stsp]

In #291 I implemented fn
0x8c which does a very
similar thing.

[ecm-pushbx]

I don't understand how this relates to calling int 23h

[stsp]

It doesn't, just a very similar
thing.