/* A sometimes minimal FORTH compiler and tutorial for Linux / i386 systems. -*- asm -*-
By Richard W.M. Jones <rich@annexia.org> http://annexia.org/forth
This is PUBLIC DOMAIN (see public domain release statement below).
- $Id: jonesforth.S,v 1.36 2007-09-27 23:09:39 rich Exp $
+ $Id: jonesforth.S,v 1.40 2007-09-29 22:12:07 rich Exp $
gcc -m32 -nostdlib -static -Wl,-Ttext,0 -o jonesforth jonesforth.S
*/
- .set JONES_VERSION,36
+ .set JONES_VERSION,39
/*
INTRODUCTION ----------------------------------------------------------------------
push %ecx
NEXT
+ defcode "?DUP",4,,QDUP // duplicate top of stack if non-zero
+ pop %eax
+ test %eax,%eax
+ jz 1f
+ push %eax
+1: push %eax
+ NEXT
+
defcode "1+",2,,INCR
incl (%esp) // increment top of stack
NEXT
*/
defvar "STATE",5,,STATE
defvar "HERE",4,,HERE,user_defs_start
- defvar "LATEST",6,,LATEST,name_SYSEXIT // SYSEXIT must be last in built-in dictionary
+ defvar "LATEST",6,,LATEST,name_SYSCALL3 // SYSCALL3 must be last in built-in dictionary
defvar "_X",2,,TX
defvar "_Y",2,,TY
defvar "_Z",2,,TZ
F_IMMED The IMMEDIATE flag's actual value.
F_HIDDEN The HIDDEN flag's actual value.
F_LENMASK The length mask in the flags/len byte.
+
+ SYS_* and the numeric codes of various Linux syscalls (from <asm/unistd.h>)
*/
+//#include <asm-i386/unistd.h> // you might need this instead
+#include <asm/unistd.h>
+
.macro defconst name, namelen, flags=0, label, value
defcode \name,\namelen,\flags,\label
push $\value
defconst "F_HIDDEN",8,,__F_HIDDEN,F_HIDDEN
defconst "F_LENMASK",9,,__F_LENMASK,F_LENMASK
+ defconst "SYS_EXIT",8,,SYS_EXIT,__NR_exit
+ defconst "SYS_OPEN",8,,SYS_OPEN,__NR_open
+ defconst "SYS_CLOSE",9,,SYS_CLOSE,__NR_close
+ defconst "SYS_READ",8,,SYS_READ,__NR_read
+ defconst "SYS_WRITE",9,,SYS_WRITE,__NR_write
+ defconst "SYS_CREAT",9,,SYS_CREAT,__NR_creat
+
/*
RETURN STACK ----------------------------------------------------------------------
exits the program, which is why when you hit ^D the FORTH system cleanly exits.
*/
-#include <asm-i386/unistd.h>
-
defcode "KEY",3,,KEY
call _KEY
push %eax // push return value on stack
NEXT
/*
- PRINTING STRINGS ----------------------------------------------------------------------
+ LITERAL STRINGS ----------------------------------------------------------------------
- LITSTRING and EMITSTRING are primitives used to implement the ." and S" operators
- (which are written in FORTH). See the definition of those operators below.
+ LITSTRING is a primitive used to implement the ." and S" operators (which are written in
+ FORTH). See the definition of those operators later.
+
+ TELL just prints a string. It's more efficient to define this in assembly because we
+ can make it a single Linux syscall.
*/
defcode "LITSTRING",9,,LITSTRING
andl $~3,%esi
NEXT
- defcode "EMITSTRING",10,,EMITSTRING
+ defcode "TELL",4,,TELL
mov $1,%ebx // 1st param: stdout
pop %edx // 3rd param: length of string
pop %ecx // 2nd param: address of string
// COLD must not return (ie. must not call EXIT).
defword "COLD",4,,COLD
.int INTERPRETER // call the interpreter loop (never returns)
- .int LIT,1,SYSEXIT // hmmm, but in case it does, exit(1).
/* This interpreter is pretty simple, but remember that in FORTH you can always override
* it later with a more powerful one!
CHAR puts the ASCII code of the first character of the following word on the stack. For example
CHAR A puts 65 on the stack.
- SYSEXIT exits the process using Linux exit syscall.
+ SYSCALL3 makes a standard Linux system call. (See <asm/unistd.h> for a list of system call
+ numbers). This is the form to use when the function takes up to three parameters.
- In this FORTH, SYSEXIT must be the last word in the built-in (assembler) dictionary because we
+ In this FORTH, SYSCALL3 must be the last word in the built-in (assembler) dictionary because we
initialise the LATEST variable to point to it. This means that if you want to extend the assembler
- part, you must put new words before SYSEXIT, or else change how LATEST is initialised.
+ part, you must put new words before SYSCALL3, or else change how LATEST is initialised.
*/
defcode "CHAR",4,,CHAR
push %eax // Push it onto the stack.
NEXT
- // NB: SYSEXIT must be the last entry in the built-in dictionary.
- defcode SYSEXIT,7,,SYSEXIT
- pop %ebx
- mov $__NR_exit,%eax
+ defcode "SYSCALL3",8,,SYSCALL3
+ pop %eax // System call number (see <asm/unistd.h>)
+ pop %ebx // First parameter.
+ pop %ecx // Second parameter
+ pop %edx // Third parameter
int $0x80
+ push %eax // Result (negative for -errno)
+ NEXT
/*
START OF FORTH CODE ----------------------------------------------------------------------
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