;; executing a definition, this code is what causes execution to resume at the
;; next word in that definition.
macro next {
- ;; RSI points to the address of the definition of the next word to execute.
- lodsq ; Load value at RSI into RAX and increment RSI
- ;; Now RAX contains the location of the next word to execute. The first 8
- ;; bytes of this word is the address of the codeword, which is what we want
- ;; to execute.
- jmp qword [rax] ; Jump to the codeword of the current word
+ ;; RSI points to the address of the definition of the next word to execute.
+ lodsq ; Load value at RSI into RAX and increment RSI
+ ;; Now RAX contains the location of the next word to execute. The first 8
+ ;; bytes of this word is the address of the codeword, which is what we want
+ ;; to execute.
+ jmp qword [rax] ; Jump to the codeword of the current word
}
;; pushr and popr work on the return stack, whose location is stored in the
;; register RBP.
macro pushr x {
- sub rbp, 8
- mov qword [rbp], x
+ sub rbp, 8
+ mov qword [rbp], x
}
macro popr x {
- mov x, [rbp]
- add rbp, 8
+ mov x, [rbp]
+ add rbp, 8
}
segment readable executable
main:
- cld ; Clear direction flag so LODSQ does the right thing.
- mov rbp, return_stack_top ; Initialize return stack
+ cld ; Clear direction flag so LODSQ does the right thing.
+ mov rbp, return_stack_top ; Initialize return stack
- mov rsi, program
- next
+ mov rsi, program
+ next
program: dq MAIN
;; word. It needs to save the old RSI and update it to point to the next word to
;; execute.
docol:
- pushr rsi ; Save old value of RSI on return stack; we will continue execution there after we are done executing this word
- lea rsi, [rax + 8] ; RAX currently points to the address of the codeword, so we want to continue at RAX+8
- next ; Execute word pointed to by RSI
+ pushr rsi ; Save old value of RSI on return stack; we will continue execution there after we are done executing this word
+ lea rsi, [rax + 8] ; RAX currently points to the address of the codeword, so we want to continue at RAX+8
+ next ; Execute word pointed to by RSI
;; This word is called at the end of a Forth definition. It just needs to
;; restore the old value of RSI (saved by 'docol') and resume execution.
EXIT:
- dq .start
+ dq .start
.start:
- popr rsi
- next
+ popr rsi
+ next
EMIT:
- dq .start
+ dq .start
.start:
- pushr rsi
- pushr rax
- mov rax, 1
- mov rdi, 1
- lea rsi, [rsp]
- mov rdx, 1
- syscall
- add rsp, 8
- popr rax
- popr rsi
- next
+ pushr rsi
+ pushr rax
+ mov rax, 1
+ mov rdi, 1
+ lea rsi, [rsp]
+ mov rdx, 1
+ syscall
+ add rsp, 8
+ popr rax
+ popr rsi
+ next
PUSH_HELLO_CHARS:
- dq .start
-.start:
- push $A
- push 'o'
- push 'l'
- push 'l'
- push 'e'
- push 'H'
- next
+ dq .start
+ .start:
+ push $A
+ push 'o'
+ push 'l'
+ push 'l'
+ push 'e'
+ push 'H'
+ next
HELLO:
- dq docol
- dq PUSH_HELLO_CHARS
- dq EMIT
- dq EMIT
- dq EMIT
- dq EMIT
- dq EMIT
- dq EMIT
- dq EXIT
+ dq docol
+ dq PUSH_HELLO_CHARS
+ dq EMIT
+ dq EMIT
+ dq EMIT
+ dq EMIT
+ dq EMIT
+ dq EMIT
+ dq EXIT
TERMINATE:
- dq .start
-.start:
- mov rax, $3C
- mov rdi, 0
- syscall
+ dq .start
+ .start:
+ mov rax, $3C
+ mov rdi, 0
+ syscall
MAIN:
- dq docol
- dq HELLO
- dq HELLO
- dq HELLO
- dq TERMINATE
+ dq docol
+ dq HELLO
+ dq HELLO
+ dq HELLO
+ dq TERMINATE
segment readable writable