[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. ]
ok.
>
> 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();
#ifdef CONFIG_DEBUG_RSTACK
printk(" >R: %x\n", tmp);
#endif
if (interpreting_bootscript == true)
pushR2(tmp);
else
PUSHR(tmp);
}
The new code would be this part:
if (interpreting_bootscript == true)
pushR2(tmp);
else
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;
feval(bootscript);
interpreting_bootscript = false;
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