;;; -*-scheme-*-

;;; Mes --- Maxwell Equations of Software
;;; Copyright © 2016 Jan Nieuwenhuizen <janneke@gnu.org>
;;;
;;; scm.mes: This file is part of Mes.
;;;
;;; Mes is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; Mes is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with Mes.  If not, see <http://www.gnu.org/licenses/>.

(define (int->bv32 value)
  (let ((bv (make-bytevector 4)))
    (bytevector-u32-native-set! bv 0 value)
    bv))

(define (int->bv16 value)
  (let ((bv (make-bytevector 2)))
    (bytevector-u16-native-set! bv 0 value)
    bv))

(define elf32-addr int->bv32)
(define elf32-half int->bv16)
(define elf32-off int->bv32)
(define elf32-word int->bv32)

(define (make-elf text data)
 (define vaddress #x08048000)

 (define ei-magic `(#x7f ,@(string->list "ELF")))
 (define ei-class '(#x01)) ;; 32 bit
 (define ei-data '(#x01)) ;; little endian
 (define ei-version '(#x01))
 (define ei-osabi '(#x00))
 (define ei-pad '(#x0 #x0 #x0 #x0 #x0 #x0 #x0 #x0))
 (define e-ident
   (append
    ei-magic
    ei-class
    ei-data
    ei-version
    ei-osabi
    ei-pad))

 (define ET-EXEC 2)
 (define EM-386 3)
 (define EV-CURRENT 1)

 (define p-filesz (elf32-word 0))
 (define p-memsz (elf32-word 0))
 (define PF-X 1)
 (define PF-W 2)
 (define PF-R 4)
 (define p-flags (elf32-word (logior PF-X PF-W PF-R)))
 (define p-align (elf32-word 1))

 (define (program-header type offset text)
   (append
    (elf32-word type)
    (elf32-off offset)
    (elf32-addr (+ vaddress offset))
    (elf32-addr (+ vaddress offset))
    (elf32-word (length text))
    (elf32-word (length text))
    p-flags
    p-align
    ))

 (define (section-header name type offset text)
   (append
    (elf32-word name)
    (elf32-word type)
    (elf32-word 3) ;; write/alloc must for data hmm
    (elf32-addr (+ vaddress offset))
    (elf32-off offset) 
    (elf32-word (length text))
    (elf32-word 0)
    (elf32-word 0)
    (elf32-word 1)
    (elf32-word 0)))


 (define e-type (elf32-half ET-EXEC))
 (define e-machine (elf32-half EM-386))
 (define e-version (elf32-word EV-CURRENT))
 (define e-entry (elf32-addr 0))
 ;;(define e-entry (elf32-addr (+ vaddress text-offset)))
 ;;(define e-phoff (elf32-off 0))
 (define e-shoff (elf32-off 0))
 (define e-flags (elf32-word 0))
 ;;(define e-ehsize (elf32-half 0))
 (define e-phentsize (elf32-half (length (program-header 0 0 '()))))
 (define e-phnum (elf32-half 1))
 (define e-shentsize (elf32-half (length (section-header 0 0 0 '()))))
 (define e-shnum (elf32-half 5))
 (define e-shstrndx (elf32-half 4))

 (define (elf-header size entry sections)
   (append
    e-ident
    e-type
    e-machine
    e-version
    (elf32-addr (+ vaddress entry)) ;; e-entry
    (elf32-off size) ;; e-phoff
    (elf32-off sections) ;; e-shoff
    e-flags
    (elf32-half size) ;; e-ehsize
    e-phentsize
    e-phnum
    e-shentsize
    e-shnum
    e-shstrndx
    ))

 (define elf-header-size
   (length (elf-header 0 0 0)))

 (define program-header-size
   (length (program-header 0 0 '())))

 (define text-offset
   (+ elf-header-size program-header-size))

 (define (program-headers)
   (append
    (program-header 1 text-offset (text 0))
    ))


 (define note
   (string->list
    (string-append
     "MES"
     ;;"Mes -- Maxwell Equations of Software\n"
     ;;"https://gitlab.com/janneke/mes"
     )
    ;; #x05 #x00 #x00 #x00 #x00 #x00 #x00 #x00 #x02 #x00 #x00 #x00
    ;; #\i #\3 #\8 #\6 #x00 #x00 #x00 #x00
    ))

 (define tab
   `(
     #x00 ,@(string->list ".shstrtab")
          #x00 ,@(string->list ".text")
          #x00 ,@(string->list ".data")
          #x00 ,@(string->list ".note")
          #x00 #x00 #x00 #x00
          ))

 (define text-length
   (length (text 0)))

 (define data-offset
   (+ text-offset text-length))

 (define data-address (+ data-offset vaddress))

 (define data-length
   (length data))

 (define note-length
   (length note))

 (define note-offset
   (+ data-offset data-length))

 (define tab-offset
   (+ note-offset note-length))

 (define tab-length
   (length tab))

 (define section-headers-offset
   (+ tab-offset tab-length))


 (define SHT-PROGBITS 1)
 (define SHT-STRTAB 3)
 (define SHT-NOTE 7)
 (define (section-headers)
   (append
    (section-header 0 0 0 '())
    (section-header 11 SHT-PROGBITS text-offset (text 0))
    (section-header 17 SHT-PROGBITS data-offset data)
    (section-header 23 SHT-NOTE note-offset note)
    (section-header 1 SHT-STRTAB tab-offset tab)
    ))

 (define exe
   (append
    (elf-header elf-header-size text-offset section-headers-offset)
    (program-headers)
    (text data-address)
    data
    note
    tab
    (section-headers)
    ))
 exe)