I think most of these solutions probably predate 8051 and ST7 cores(which both have stack pointers) where I ran into them but reduced memory models are still pretty useful for them, due to the overhead vs RAM usually fitted. It's too late to edit my comment. I'll mostly discuss the fallout from static stack variable allocation.

From https://www.st.com/resource/en/user_manual/um0015-st7-8bit-m... (8.3.5 Limitations put on the full implementation of C language)(I think this is talking about Hicross C, but COSMIC and Raisonance work the same depending on stack memory model): The ST7 family provides a limited RAM size, of which the stack takes only a part, that can be as small as 64 bytes. This does not allow the use of the stack for parameter passing. Thus, the implementation of C for the ST7 uses registers and a few memory locations to pass the parameters, and allocates local variables to RAM just like global variables. This works the same way as in a typical implementation, but with the following restrictions...

You can still get an evaluation copy of COSMIC C and try this out. Here I made a function call itself void port_init(void){port_init();}. Note that this error comes from the linker, clnk, not the compiler, because the linker is responsible for stack allocation globally, as described above): #error clnk vumeter.lkf:1 function _port_init is recursive.

There's a similar error if you call a function from anything called from main() and also from any interrupt entry point. This is because the memory model isn't re-entrant, so calling the same function from >1 path can cause them to overlap, corrupting their staticly allocated variables.

https://www.cosmicsoftware.com/pdf/RX.pdf has an explanation for "is recursive" and "is reentrant".

COMSIC C will also let you compile enum {x = x}, but I don't know what value x gets.