Le lun 21/04/2003 à 03:31, Pierre Pronchery a écrit :
> On Mon, 21 Apr 2003 00:31:13 +0200
> Lucas Nussbaum <lucas@???> wrote:
> > > Créer un programme Hello, World!, le plus petit possible. Le
> > > programme doit afficher Hello, World! à l'écran quand il est
> > > appelé sans arguments. Il doit ensuite se terminer en renvoyant
> > > au shell un code de retour de zéro. Tout ça sous Linux,
> > > évidemment !
> > $ wc -c hello
> > 716 hello
> Pas mal du tout, bonne idee.
> Peut mieux faire? En C cela ne doit pas etre evident.
> Aide par google, j'avoue, j'ai obtenu le fichier suivant:
>
> New record!
>
> --
> Pierre
Google trouve mieux....
i386, linux 2.4.21-pre5-ac3-jna3, nasm 0.98
[jnavila@origan jnavila]$ cat hello-2.2.17.asm
;; hello.asm: Copyright (C) 2001 by Brian Raiter, under the GNU
;; General Public License (version 2 or later). No warranty.
;;
;; To build:
;; nasm -f bin -o hello hello-2.2.17.asm && chmod +x hello
BITS 32
org 0x05936000
db 0x7F, "ELF"
dd 1
dd 0
dd $$
dw 2
dw 3
_start: inc eax ; 1 == exit syscall no.
mov dl, 13 ; set edx to length of
message
cmp al, _start - $$
pusha ; save eax and ebx
xchg eax, ebx ; set ebx to 1 (stdout)
add eax, dword 4 ; 4 == write syscall no.
mov ecx, msg ; point ecx at message
int 0x80 ; eax = write(ebx, ecx,
edx)
popa ; set eax to 1 and ebx
to 0
int 0x80 ; exit(bl)
dw 0x20
dw 1
msg: db 'hello, world', 10
;; This is how the file looks when it is read as an ELF header,
;; beginning at offset 0:
;;
;; e_ident: db 0x7F, "ELF" ; required
;; db 1 ; 1 = ELFCLASS32
;; db 0 ; (garbage)
;; db 0 ; (garbage)
;; db 0x00, 0x00, 0x00, 0x00, 0x00 ; (unused)
;; db 0x00, 0x60, 0x93, 0x05
;; e_type: dw 2 ; 2 = ET_EXE
;; e_machine: dw 3 ; 3 = EM_386
;; e_version: dd 0x3C0DB240 ; (garbage)
;; e_entry: dd 0x05936014 ; program starts
here
;; e_phoff: dd 4 ; phdrs located
here
;; e_shoff: dd 0x93602EB9 ; (garbage)
;; e_flags: dd 0x6180CD05 ; (unused)
;; e_ehsize: dw 0x80CD ; (garbage)
;; e_phentsize: dw 0x20 ; phdr entry
size
;; e_phnum: dw 1 ; one phdr in
the table
;; e_shentsize: dw 0x6568 ; (garbage)
;; e_shnum: dw 0x6C6C ; (garbage)
;; e_shstrndx: dw 0x2C6F ; (garbage)
;;
;; This is how the file looks when it is read as a program header
;; table, beginning at offset 4:
;;
;; p_type: dd 1 ; 1 = PT_LOAD
;; p_offset: dd 0 ; read from top
of file
;; p_vaddr: dd 0x05936000 ; load at this
address
;; p_paddr: dd 0x00030002 ; (unused)
;; p_filesz: dd 0x3C0DB240 ; a tad bit
large ...
;; p_memsz: dd 0x0593600D ; also excessive
;; p_flags: dd 4 ; 4 = PF_R (no
PF_X?)
;; p_align: dd 0x2EB9 ; (garbage)
;;
;; Note that the top three bytes of the file's origin (0x60 0x93 0x68)
;; translate to "pusha", "xchg eax, ebx", and the first byte of "add
;; eax, IMM".
;;
;; The fields marked as unused are either specifically documented as
;; not being used, or not being used with 386-based implementations.
;; Some of the fields marked as containing garbage are not used when
;; loading and executing programs. Other fields containing garbage are
;; accepted because Linux currently doesn't examine then.
[jnavila@origan jnavila]$ nasm -f bin -o hello hello-2.2.17.asm && chmod
+x hello
[jnavila@origan jnavila]$ wc -c hello
59 hello
[jnavila@origan jnavila]$ ./hello && echo ni!
hello, world
ni!
Le gars utilise des champs du header elf pour son programme.
Effectivement, c'est impressionnant...
