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|
; (hint:tabulation size is 3)
; (date-dd-mm-yyyy:03/01/2007)
; Creating a fully functional ELF file without even GNU/ld
; ---------------------------------------------------------
;
; This a pattern file which allow you to create ELF executable without
; even a linker in hands. This is useful for custom installation with
; low resource, such as old PC. Indeed, the usual way is to use GNU/ld,
; but unfortunatly, ld rely on glibc, which is very-very hugh en
; outrageously resource consuming.
;
; You can use it with nasm (the syntax used here is the one of nasm).
; A static version of nasm if very light (between 150 and 200KB). So
; with a static version of e3 (which is no more than 13KB), and
; a few text files documentations about syscalls and some other good
; stuff, you can have a real developpement environement under less
; than the quarter of an 1.44M floppy disk.
;
; Please visit http://www.les-ziboux.rasama.org/elf-without-ld.html
; for updates. In the futur, I will mirror a very small static version
; of nasm (102KB), a static version of e3, and some useful texte
; documentation.
;
; You can use this pattern in any project... it is not mandatory, but this
; would be very nice of you to put this url on top of your product sources :
; http://www.les-ziboux.rasama.org/elf-without-ld.html
; Thank you :)
;
; To use this pattern, just edit the place between the BEGIN and END mark,
; both in code and data segment.
;
; If you code only adress read-only data, then you can use the other
; "elf-simple.asm", beceause is there are only read-only datas, it is
; best to put them in code segment.
;
; Finaly you have to compile your code with "nasm -f bin [-O2] yourcode.asm"
; (the -O parameter is optional, alghtough often requited because of
; short-jumps and some stuff like that).
; This file is full of comments... you may remove them after reading ;)
;
; Comments are welcome : les-ziboux@rasama.org (fr/en)
; You wanna learn Arabic ? -> http://www.les-ziboux.rasama.org (fr)
cpu 386
bits 32
org 0x08048000 ; Linux applications are loaded at this virtual address.
; === Header ================================================================
elf_header:
.start
db 0x7F, "ELF" ; ELF signature -- constant
db 1 ; Architecture(1) -- 1 = 32 bits
db 1 ; Data enconding -- 1 = LSB-First
db 1 ; File version -- 1 = v1
db 0,0,0,0,0,0,0,0,0 ; 9 bytes padding -- should be zero
dw 2 ; Type -- 2 = executable
dw 3 ; Architecture(2) -- 3 = i386
dd 1 ; ELF Version -- 1 = ELF-v1
dd _start ; Entry point adress in memory -- virtual adress
dd segments_table - $$ ; Segments table offset in file
dd 0 ; Sections table offset in file -- 0 = none)
dd 0 ; File's flags
dw elf_header.size ; ELF Header's size
dw 32 ; Segments table entries's size
dw 2 ; Number of segment descriptors
dw 0 ; Sections table entries's size -- 0 = none
dw 0 ; Number of sections descriptor -- 0 = none
dw 0 ; String table index -- 0 = none
.size equ $ - .start
segments_table:
code_segment_descriptor:
.start:
dd 1 ; Type -- 1 = loadable into memory
dd 0 ; Offset in file -- include ELF header and table
dd $$ ; Virtual address in memory
dd 0 ; Physical adress -- 0 = no physical address
dd code_size ; Size in file
dd code_size ; Size in memory
dd 5 ; Permission flags -- 0x4 + 0x1 = read and execute
dd 0x4 ; Alignment in memory (and in file)
.size equ $ - .start
data_segment_descriptor:
.start:
dd 1 ; Type -- 1 = loadable into memory
dd _data - $$ ; Offset in file
dd _data ; Virtual adress in memory
dd 0 ; Physical adress -- 0 = no physical address
dd data_size ; Size in file
dd data_size ; Size in memory
dd 6 ; Permission flags -- 0x4 + 0x2 = read and write
dd 0x4 ; Alignment in memory (and in file)
.size equ $ - .start
; === Code ==================================================================
_code :
_start: ; You can move the start label where-ever you want in code segment.
; ----- BEGIN of your code -----
; Here is a sample code which simply say good bye and terminate.
; It give an example of usage of both code segment and data
; segment. Although this example does write to data segment,
; the data segment is still fully writable. Note that read-only
; datas can also reside in code segment (you should use
; the pattern "elf-simple.asm" for this purpose).
; You can put your own code between the BEGIN and END mark.
; Do not modify something else, unless you're sure about what
; you are playing with.
mov eax, 4 ; function id for sys_write
mov ebx, 1 ; descriptor of standard output
mov ecx, message ; offset of bytes to write
mov edx, message.length ; number of bytes to write
int 0x80 ; syscall
mov eax, 1 ; function id for sys_exit
mov ebx, 0 ; return code from the program (0 mean Ok)
int 0x80 ; syscall
; ----- END of your code -----
align 4
code_size equ $ - $$
; === Data ==================================================================
align 4
_data:
; ----- BEGIN of your datas -----
; This is a simple data example. This data segment is writable.
; Note that you can put read-only data in the code segment. If you
; only have read-only data, and no writable data in you application,
; then putting them in code segmet, avoid the creation of a data
; segment, reducing a bit the size of the executable. For this
; purpose, use the other patten name "elf-simple.asm".
; You can put your own datas between the BEGIN and END mark.
; Do not modify something else, unless you're sure about what
; you are playing with.
message:
db "Bye, Au-revoir, Ma'a as-salama, Bisbald ... :)", 10
.length equ $ - message
; ----- END of your datas -----
align 4
data_size equ $ - _data |
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