🚀 go-pugleaf

James Kanze US/ESC 60/3/141 #40763 writes:
|> Konrad Schwarz writes:
|> 
|> |> J. Kanze writes:
|> |> |>     [Concerning alloca...]
|> |> I: As far as I know, implementing alloca via the stack is trivial on
|> |> I: any general-purpose CPU, but I am interested in hearing of counter examples.
|> |> |> 
|> |> |> So what do you do on machines that don't have a stack?
|> 
|> |> General-purpose CPU's have stacks, at least in my book.
|> 
|> IBM mainframes don't have stacks.  Would you not consider them general
|> purpose CPU's?  (While most modern architectures have stacks, I
|> suspect that if you looked at all of the general-purpose CPU's in
|> existance, you'd find more architectures without a stack than with.)

You're telling me that a C implementation on an IBM mainframe doesn't
use a register as a stack pointer or doesn't reserve a continuous
region of memory as a stack?

Note that you'd be hard pressed to find a RISC machine with a dedicated
stack pointer register.

|> |> How do you
|> |> implement C on machines that don't have a stack?
|> 
|> The same way you implement any other language, I suppose.  On the one
|> machine I have any experience with, local frames were allocated and

Is this the afore mentioned IBM mainframe?  Was the language C---or
SIMULA :)?

|> freed using a mechanism similar to malloc/free.  Once allocated, the
|> size of the local frame could not be changed.

See my previous postings for how to implement alloca in this case.

Konrad Schwarz