[OpenBIOS] Implementing a second return stack

Programmingkid programmingkidx at gmail.com
Sun Apr 17 04:44:47 CEST 2016

On Apr 16, 2016, at 10:19 PM, Segher Boessenkool wrote:

> On Sat, Apr 16, 2016 at 10:11:36PM -0400, Programmingkid wrote:
>> Mac OS 9 does alter the return stack in OpenBIOS. This is perceived to be unacceptable. The solution to this issue has been stated as implementing a second return stack. This stack would just be an array that implements push and pull calls. 
>> In the bootinfo_load.c file, in the bootinfo_init_program() function is where the Mac OS 9 boot script is read into memory, into the bootscript variable. What I want to do is replace all >r and r> calls in the bootscript buffer with other words. Something like substitute>r and substitute_r>. These words would use a separate array to push and pop data from. I think this would work because Mac OS 9's boot script only uses the return stack for data storage. Does this sound like the right thing to do?
> [ Please wrap your lines, this is unreadable.  Thanks. ]


> No; just implement a version of >R etc. that work in interpret mode.  Like
> : >r  state @ IF postpone >r EXIT THEN
>      ( and here, do the push to the simulated R stack ) ; IMMEDIATE
> (And easier/cleaner/nicer if your system has separate compile and interpret
> behaviours for all words, or a separate compiler wordlist).

>r is implemented in forth.c in c. So what do you think about this:

 *  >r          ( x -- ) (R: -- x )

static void tor(void)
	ucell tmp = POP();
	printk("  >R: %x\n", tmp);
    if (interpreting_bootscript == true)

The new code would be this part:
    if (interpreting_bootscript == true)

pushR2() would push into another array that isn't the return stack. 

interpreting_bootscript would be a global variable that is set in
the bootinfo_init_program() function right before the call to
feval() that runs the bootscript. This variable would be set to
false right after the call to feval(). Basically this:

interpreting_bootscript = true;
interpreting_bootscript = false;

More information about the OpenBIOS mailing list