X-Git-Url: https://git.rrq.au/?a=blobdiff_plain;f=main.asm;h=af84a66631a0d17d5abb5922a220130f9135f8b4;hb=3e2708b7e8434cc0678c8ee0c315166704c8f31a;hp=c5758d8b23adfc1104682493de7efebd39634fc3;hpb=8c833141e36f00610bee5d20d058815423533b57;p=rrq%2Fjonasforth.git diff --git a/main.asm b/main.asm index c5758d8..af84a66 100644 --- a/main.asm +++ b/main.asm @@ -4,97 +4,233 @@ format ELF64 executable ;; 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 HELLO +program: dq MAIN ;; The codeword is the code that will be executed at the beginning of a forth ;; 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 codeword is called at the end of a Forth definition. It just needs to +;; 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: - popr rsi - next +EXIT: + dq .start +.start: + popr rsi + next + +;; LIT is a special word that reads the next "word pointer" and causes it to be +;; placed on the stack rather than executed. +LIT: + dq .start +.start: + lodsq + push rax + next +;; 0BRANCH is the fundamental mechanism for branching. If the top of the stack +;; is zero, we jump by the given offset. 0BRANCH is given the offset as an +;; integer after the word. +ZBRANCH: + dq .start +.start: + ;; Compare top of stack to see if we should branch + pop rax + cmp rax, 0 + jnz .dont_branch +.do_branch: + add rsi, [rsi] ; [RSI], which is the next word, contains the offset; we add this to the instruction pointer. + next ; Then, we can just continue execution as normal +.dont_branch: + add rsi, 8 ; We need to skip over the next word, which contains the offset. + next + +;; Expects a character on the stack and prints it to standard output. 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 + +;; Prints a newline to standard output. +NEWLINE: + dq docol + dq LIT, $A + dq EMIT + dq EXIT + +;; Read a word from standard input and push it onto the stack as a pointer and a +;; size. The pointer is valid until the next call to READ_WORD. +READ_WORD: ; 400170 + 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 + mov [.rsi], rsi + mov [.rax], rax + +.skip_whitespace: + ;; Read characters into .char_buffer until one of them is not whitespace. + mov rax, 0 + mov rdi, 0 + mov rsi, .char_buffer + mov rdx, 1 + syscall + + cmp [.char_buffer], ' ' + je .skip_whitespace + cmp [.char_buffer], $A + je .skip_whitespace + +.alpha: + ;; We got a character that wasn't whitespace. Now read the actual word. + mov [.length], 0 + +.read_alpha: + mov al, [.char_buffer] + movzx rbx, [.length] + mov rsi, .buffer + add rsi, rbx + mov [rsi], al + inc [.length] + + mov rax, 0 + mov rdi, 0 + mov rsi, .char_buffer + mov rdx, 1 + syscall + + cmp [.char_buffer], ' ' + je .end + cmp [.char_buffer], $A + jne .read_alpha + +.end: + push .buffer + movzx rax, [.length] + push rax + + mov rsi, [.rsi] + mov rax, [.rax] + + next + +;; Takes a string (in the form of a pointer and a length on the stack) and +;; prints it to standard output. +TYPE: + dq .start +.start: + mov rbx, rsi + mov rcx, rax + + mov rax, 1 + mov rdi, 1 + pop rdx ; Length + pop rsi ; Buffer + syscall + + mov rax, rcx + mov rsi, rbx + next + +;; Exit the program cleanly. +TERMINATE: + dq .start +.start: + mov rax, $3C + mov rdi, 0 + syscall PUSH_HELLO_CHARS: - dq .start + dq docol + dq LIT, $A + dq LIT, 'o' + dq LIT, 'l' + dq LIT, 'l' + dq LIT, 'e' + dq LIT, 'H' + dq EXIT + +PUSH_YOU_TYPED: + dq .start .start: - push $A - push 'o' - push 'l' - push 'l' - push 'e' - push 'H' - next + push you_typed_string + push you_typed_string.length + next HELLO: - dq docol - dq PUSH_HELLO_CHARS - dq EMIT - dq EMIT - dq EMIT - dq EMIT - dq EMIT - dq EMIT - dq exit - -PROGRAM: - dq docol - dq HELLO - dq HELLO - dq HELLO - dq exit + dq docol + dq LIT, 'H', EMIT + dq LIT, 'e', EMIT + dq LIT, 'l', EMIT + dq LIT, 'l', EMIT + dq LIT, 'o', EMIT + dq LIT, '!', EMIT + dq NEWLINE + dq EXIT + +MAIN: + dq docol + dq HELLO + dq READ_WORD + dq LIT, you_typed_string + dq LIT, you_typed_string.length + dq TYPE + dq TYPE + dq NEWLINE + dq HELLO + dq TERMINATE segment readable writable +you_typed_string db 'You typed: ' +.length = $ - you_typed_string + +READ_WORD.rsi dq ? +READ_WORD.rax dq ? +READ_WORD.max_size = $FF +READ_WORD.buffer rb READ_WORD.max_size +READ_WORD.length db ? +READ_WORD.char_buffer db ? + ;; Return stack rq $2000 return_stack_top: