X-Git-Url: https://git.rrq.au/?a=blobdiff_plain;f=main.asm;h=183be74435f3b7091edd50c08ce92d3076434640;hb=412aa1087846d432ddc5bb93c3dcb2acf292010c;hp=626de1610f6d360e0331ce54ea12338f194bc84e;hpb=28f8191da1b2b3131946545a2a62d7ed558ee625;p=rrq%2Fjonasforth.git diff --git a/main.asm b/main.asm index 626de16..183be74 100644 --- a/main.asm +++ b/main.asm @@ -4,90 +4,399 @@ 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 } +;; The following macro generates the dictionary header. It updates the +;; initial_latest_entry variable, which is used as the initial value of the +;; latest_entry variable that is made available at runtime. +;; +;; The header contains a link to the previous entry, the length of the name of +;; the word and the word itself as a string literal. +;; +;; This macro also defines a label LABEL_entry. +initial_latest_entry = 0 +macro header label, name { + local .string_end + +label#_entry: + dq initial_latest_entry + db .string_end - ($ + 1) + db name + .string_end: +label: + +initial_latest_entry = label#_entry +} + +;; Define a Forth word that is implemented in assembly. See 'header' for details. +macro forth_asm label, name { + header label, name + dq .start +.start: +} + +;; Define a Forth word that is implemented in Forth. (The body will be a list of +;; 'dq' statements.) +macro forth label, name { + header label, name + dq docol +} + + + segment readable executable +entry main + +include "impl.asm" + 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 rax, MAIN + jmp qword [rax] -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 +forth_asm EXIT, 'EXIT' + popr rsi + next -EMIT: - 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 - -PUSH_HELLO_CHARS: - 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 +;; LIT is a special word that reads the next "word pointer" and causes it to be +;; placed on the stack rather than executed. +forth_asm LIT, 'LIT' + lodsq + push rax + next + +;; Given a string (a pointer following by a size), return the location of the +;; dictionary entry for that word. If no such word exists, return 0. +forth_asm FIND, 'FIND' + mov [.rsi], rsi + + pop [find.search_length] + pop [find.search_buffer] + mov rsi, [latest_entry] ; Start with the last added word + call find + push rsi + + mov rsi, [.rsi] + next + push rsi + + mov rsi, [.rsi] + next + +;; Given an entry in the dictionary, return a pointer to the codeword of that +;; entry. +forth_asm TCFA, '>CFA' + pop rax + add rax, 8 ; [rax] = length of name + movzx rbx, byte [rax] + inc rax + add rax, rbx ; [rax] = codeword + push rax + next + +;; BRANCH is the fundamental mechanism for branching. BRANCH reads the next word +;; as a signed integer literal and jumps by that offset. +forth_asm BRANCH, '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 + +;; 0BRANCH is like BRANCH, but it jumps only if the top of the stack is zero. +forth_asm ZBRANCH, '0BRANCH' + ;; Compare top of stack to see if we should branch + pop rax + cmp rax, 0 + jnz .dont_branch +.do_branch: + jmp BRANCH.start +.dont_branch: + add rsi, 8 ; We need to skip over the next word, which contains the offset. + next + +;; Duplicate the top of the stack. +forth_asm DUP_, 'DUP' + push qword [rsp] + next + +;; Execute the codeword at the given address. +forth_asm EXEC, 'EXEC' + pop rax + jmp qword [rax] + +;; Expects a character on the stack and prints it to standard output. +forth_asm EMIT, 'EMIT' + 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. +forth NEWLINE, 'NEWLINE' + dq LIT, $A + dq EMIT + dq EXIT + +;; Prints a space to standard output. +forth SPACE, 'SPACE' + dq LIT, ' ' + 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. +forth_asm READ_WORD, 'READ-WORD' + mov [.rsi], rsi + + call read_word + push rdi ; Buffer + push rdx ; Length + + mov rsi, [.rsi] + next + +;; Takes a string on the stack and replaces it with the decimal number that the +;; string represents. +forth_asm PARSE_NUMBER, 'PARSE-NUMBER' + pop [parse_number.length] ; Length + pop [parse_number.buffer] ; String pointer + + push rsi + call parse_number + pop rsi + + push rax ; Result + next + +forth READ_NUMBER, 'READ-NUMBER' + dq READ_WORD + dq PARSE_NUMBER + dq EXIT + +;; Takes a string (in the form of a pointer and a length on the stack) and +;; prints it to standard output. +forth_asm TELL, 'TELL' + 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. +forth_asm TERMINATE, 'TERMINATE' + mov rax, $3C + mov rdi, 0 + syscall + +forth HELLO, 'HELLO' + 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 + +;; Duplicate a pair of elements. +forth_asm PAIRDUP, '2DUP' + pop rbx + pop rax + push rax + push rbx + push rax + push rbx + next + +;; Swap the top two elements on the stack. +forth_asm SWAP, 'SWAP' + pop rax + pop rbx + push rax + push rbx + next + +;; Remove the top element from the stack. +forth_asm DROP, 'DROP' + add rsp, 8 + next + +;; The INTERPRET word reads and interprets user input. It's behavior depends on +;; the current STATE. It provides special handling for integers. (TODO) +forth INTERPRET, 'INTERPRET' + ;; Read word + dq READ_WORD + dq PAIRDUP + ;; Stack is (word length word length). + dq FIND ; Try to find word + dq DUP_ + dq ZBRANCH, 8 * 8 ; Check if word is found + + ;; Word is found, execute it + dq TCFA + ;; Stack is (word length addr) + dq SWAP, DROP + dq SWAP, DROP + ;; Stack is (addr) + dq EXEC + dq EXIT + + ;; No word is found, assume it is an integer literal + ;; Stack is (word length addr) + dq DROP + dq PARSE_NUMBER + dq EXIT + +;; .U prints the value on the stack as an unsigned integer in hexadecimal. +forth_asm DOTU, '.U' + mov [.length], 0 + mov [.printed_length], 1 + pop rax ; RAX = value to print + push rsi ; Save value of RSI + + ;; We start by constructing the buffer to print in reverse + +.loop: + mov rdx, 0 + mov rbx, $10 + div rbx ; Put remainer in RDX and quotient in RAX + + ;; Place the appropriate character in the buffer + mov rsi, .chars + add rsi, rdx + mov bl, [rsi] + mov rdi, .rbuffer + add rdi, [.length] + mov [rdi], bl + inc [.length] + + ;; .printed_length is the number of characters that we ulitmately want to + ;; print. If we have printed a non-zero character, then we should update + ;; .printed_length. + cmp bl, '0' + je .skip_updating_real_length + mov rbx, [.length] + mov [.printed_length], rbx +.skip_updating_real_length: + + cmp [.length], 16 + jle .loop + + ;; Flip buffer around, since it is currently reversed + mov rcx, [.printed_length] +.flip: + mov rsi, .rbuffer + add rsi, rcx + dec rsi + mov al, [rsi] + + mov rdi, .buffer + add rdi, [.printed_length] + sub rdi, rcx + mov [rdi], al + + loop .flip + + ;; Print the buffer + mov rax, 1 + mov rdi, 1 + mov rsi, .buffer + mov rdx, [.printed_length] + syscall + + ;; Restore RSI and continue execution + pop rsi + next + +;; Takes a value and an address, and stores the value at the given address. +forth_asm PUT, '!' + pop rbx ; Address + pop rax ; Value + mov [rbx], rax + next + +;; Takes an address and returns the value at the given address. +forth_asm GET, '@' + pop rax + mov rax, [rax] + push rax + next + +;; Get the location of the STATE variable. It can be set with '!' and read with +;; '@'. +forth STATE, 'STATE' + dq LIT, var_STATE + dq EXIT + +forth MAIN, 'MAIN' + dq HELLO + dq INTERPRET + dq BRANCH, -8 * 2 + dq TERMINATE segment readable writable +latest_entry dq initial_latest_entry + +;; The STATE variable is 0 when the interpreter is executing, and non-zero when +;; it is compiling. +var_STATE dq 0 + +FIND.rsi dq ? + +READ_WORD.rsi dq ? +READ_WORD.rbp dq ? + +DOTU.chars db '0123456789ABCDEF' +DOTU.buffer rq 16 ; 64-bit number has no more than 16 digits in hex +DOTU.rbuffer rq 16 +DOTU.length dq ? +DOTU.printed_length dq ? + ;; Return stack rq $2000 return_stack_top: