;; vim: syntax=fasm
-format ELF64 executable
-
-;; "Syscalls" {{{
-
-;; [NOTE] Volatile registers Linux (syscalls) vs UEFI
+;; At compile-time we load the module given by the environment variable
+;; OS_INCLUDE. All of the following these procedures should preserve the value
+;; of RSI and RSP. They may use other registers as they like.
;;
-;; Linux syscalls: RAX, RCX, R11
-;; UEFI: RAX, RCX, R11, RDX, R8, R9, R10
-
-;; We are in the process of replacing our dependency on Linux with a dependency
-;; on UEFI. The following macros attempt to isolate what would be syscalls in
-;; Linux; thus, we will be able to replace these with UEFI-based implementations,
-;; and in theory we should expect the program to work.
-
-;; Print a string of a given length.
+;; The module should provide the following:
;;
-;; Input:
-;; - RCX = Pointer to buffer
-;; - RDX = Buffer length
+;; os_code_section
+;; Macro to start the text segment.
;;
-;; Clobbers: RAX, RCX, R11, RDI, RSI
-macro sys_print_string {
- mov rax, 1
- mov rdi, 1
- mov rsi, rcx
- syscall
-}
-
-;; Read a character from the user into the given buffer.
+;; os_data_section
+;; Macro to start the data segment.
;;
-;; Input:
-;; - RSI = Character buffer
+;; os_initialize
+;; Called at initialization.
;;
-;; Output:
-;; - BYTE [RSI] = Character
+;; os_print_string
+;; Takes a string buffer in RCX and the length in RDX, and prints the string
+;; to the console.
;;
-;; Clobbers: RAX, RCX, R11, RDI, RSI, RDX
-macro sys_read_char {
- mov rax, 0
- mov rdi, 0
- mov rdx, 1
- syscall
-}
-
-macro sys_terminate code {
- mov rax, $3C
- mov rdi, code
- syscall
-}
-
-;; }}}
+;; os_read_char
+;; Wait for the user to type a key, and then put the corresponding ASCII byte
+;; into RAX.
+;;
+;; os_terminate
+;; Shut down the system, returning the error code given in RAX.
+include '%OS_INCLUDE%'
;; The code in this macro is placed at the end of each Forth word. When we are
;; executing a definition, this code is what causes execution to resume at the
.start:
}
-segment readable executable
-
-entry main
+os_code_section
include "impl.asm" ; Misc. subroutines
include "bootstrap.asm" ; Forth words encoded in Assembly
cld ; Clear direction flag so LODSQ does the right thing.
mov rbp, return_stack_top ; Initialize return stack
+ call os_initialize
+
mov rax, MAIN
jmp qword [rax]
push rax
next
+;; When LITSTRING is encountered while executing a word, it instead reads a
+;; string from the definition of that word, and places that string on the stack
+;; as (buffer, length).
+forth_asm LITSTRING, 'LITSTRING'
+ lodsb
+ push rsi ; Buffer
+ movzx rax, al
+ push rax ; Length
+ add rsi, rax ; Skip over string before resuming execution
+ 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'
lea rcx, [rsp]
mov rdx, 1
- sys_print_string
+ call os_print_string
add rsp, 8
popr rax
popr rsi
next
-;; Read a word 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'
+;; Read a single character from the current input stream. Usually, this will wait
+;; for the user to press a key, and then return the corresponding character. When
+;; reading from a special buffer, it will instead return the next characater from
+;; that buffer.
+;;
+;; The ASCII character code is placed on the stack.
+forth_asm KEY, 'KEY'
+ call .impl
+ push rax
+ next
+
+;; Result in RAX
+.impl:
;; Are we reading from user input or from the input buffer?
cmp [input_buffer], 0
jne .from_buffer
;; Reading user input
- mov [.rsi], rsi
-
- call read_word
- push rdi ; Buffer
- push rdx ; Length
-
- mov rsi, [.rsi]
- next
+ call os_read_char
+ ret
.from_buffer:
;; Reading from buffer
- mov [.rsi], rsi
+ mov rax, [input_buffer]
+ movzx rax, byte [rax]
- mov rsi, [input_buffer]
- mov rcx, [input_buffer_length]
+ inc [input_buffer]
+ dec [input_buffer_length]
+ ret
- call pop_word
+;; Read a word 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'
+ push rsi
+.skip_whitespace:
+ ;; Read characters until one of them is not whitespace.
+ call KEY.impl
+ ;; We consider newlines and spaces to be whitespace.
+ cmp al, ' '
+ je .skip_whitespace
+ cmp al, $A
+ je .skip_whitespace
+
+ ;; We got a character that wasn't whitespace. Now read the actual word.
+ mov [.length], 0
- mov [input_buffer], rsi ; Updated buffer
- mov [input_buffer_length], rcx ; Length of updated buffer
- push rdi ; Word buffer
- push rdx ; Length of word buffer
+.read_alpha:
+ movzx rbx, [.length]
+ mov rsi, .buffer
+ add rsi, rbx
+ mov [rsi], al
+ inc [.length]
+
+ call KEY.impl
+
+ cmp al, ' '
+ je .end
+ cmp al, $A
+ jne .read_alpha
+
+.end:
+ pop rsi
+ push .buffer
+ movzx rax, [.length]
+ push rax
- mov rsi, [.rsi]
next
;; Takes a string on the stack and replaces it with the decimal number that the
pop rdx ; Length
pop rcx ; Buffer
- sys_print_string
+ call os_print_string
popr rsi
popr rax
;; Exit the program cleanly.
forth_asm TERMINATE, 'TERMINATE'
- sys_terminate 0
+ mov rax, 0
+ call os_terminate
;; Duplicate a pair of elements.
forth_asm PAIRDUP, '2DUP'
;; Print the buffer
mov rcx, .buffer
mov rdx, [.printed_length]
- sys_print_string
+ call os_print_string
;; Restore RSI and continue execution
pop rsi
mov [.length], 0
.read_char:
- mov rsi, .char_buffer
- sys_read_char
-
- mov al, [.char_buffer]
+ call os_read_char
cmp al, '"'
je .done
dq LIT, input_buffer_length
dq EXIT
-segment readable writable
+os_data_section
;; The LATEST variable holds a pointer to the word that was last added to the
;; dictionary. This pointer is updated as new words are added, and its value is
DOTU.length dq ?
DOTU.printed_length dq ?
+KEY.buffer dq ?
+
+READ_WORD.buffer rb $FF
+READ_WORD.length db ?
+
;; Reserve space for compiled words, accessed through HERE.
here dq here_top
here_top rq $4000
rq $2000
return_stack_top:
-segment readable
-
;; We store some Forth code in sys.f that defined common words that the user
;; would expect to have available at startup. To execute these words, we just
;; include the file directly in the binary, and then interpret it at startup.
-sysf file 'sys.f'
+sysf:
+file 'sys.f'
+file 'example.f'
sysf.len = $ - sysf
projects / rrq / jonasforth.git / blobdiff