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Re: Forth on ARM64

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On Thu, 3 Sep 2026 20:51:14 -0000 (UTC)
antispam@fricas.org (Waldek Hebisch) wrote:

> Under Linux on ARM64 trying to set machine stack pointer to
> value which is not divisible by 16 leads to error.  AFAICS this
> means that in default setting machine stack pointer is not
> usable as as Forth user stack pointer or return stack pointer.
> I wonder what Forth implementation do?  Do they use different
> registers as user and return stack pointer?  Maybe they use
> machine stack pointer for control and locals?  Or maybe some
> system magic removes the restriction?
> 

Here is the register assignments for the token VM I wrote for 
ARM64 for lxf 64

/*
VM8 assembler based aarch64 vm for lxf64 Forth
Copyright 2020 Peter Fälth

Register usage
	X19	ip	vm instruction pointer
    	x20	TOP	top of stack cached in x20
	x21	sp	vm stack pointer
    	x22	rp	vm return stack pointer
	x23	fp	vm floating point stack pointer
	x24	lp	vm local stack pointer
	x25	idx	loop index of innermost loop
    	x26 	limit 	loop limit of innermost loop
	x27	address of jump table
	d8	FTOP	top of float stack cached in d8

sequence to nest to next opcode is RELOAD

	ldrb	w0, [x19], 1			load opcode byte at ip, advance ip by 1
	ldr	x2, [x27, x0, lsl 3]		load address of machine code from jmptable+opcode*8
	br	x2				jump to next machine code

*/

There are just 2 calls in the hole VM, in these cases 2 registers are 
pushed to maintain 16 byte alignment.

You can avoid the 16 byte alignment by using a register other then sp
for the processor stack. My tests showed this code to be about 30% slower
in execution speed.

BR
Peter

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Thread

Forth on ARM64 antispam@fricas.org (Waldek Hebisch) - 2026-09-03 20:51 +0000
  Re: Forth on ARM64 peter <peter.noreply@tin.it> - 2026-09-04 07:33 +0200
    Re: Forth on ARM64 albert@spenarnc.xs4all.nl - 2026-09-04 10:21 +0200
      Re: Forth on ARM64 antispam@fricas.org (Waldek Hebisch) - 2026-09-04 21:19 +0000
        Re: Forth on ARM64 peter <peter.noreply@tin.it> - 2026-09-04 23:51 +0200
        Re: Forth on ARM64 albert@spenarnc.xs4all.nl - 2026-09-05 13:11 +0200
        Re: Forth on ARM64 Paul Rubin <no.email@nospam.invalid> - 2026-09-05 15:49 -0700
          Re: Forth on ARM64 antispam@fricas.org (Waldek Hebisch) - 2026-09-05 23:39 +0000
    Re: Forth on ARM64 antispam@fricas.org (Waldek Hebisch) - 2026-09-04 22:25 +0000
      Re: Forth on ARM64 peter <peter.noreply@tin.it> - 2026-09-05 09:54 +0200

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