elf executable with dynamic linker... from scratch

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snify

Joined: 02 Dec 2004
Posts: 39

snify 14 Oct 2007, 11:20

dude, same problem. *please* check this cause I need it for my compiler
32bit elf gtk example (fixed):

Code:

use32
BASE=BASE32
ENTRYPOINT=start
ELF_TYPE=ET_EXEC
ELF_PHEADER_ENTRY_SIZE=ELF_PHEADER_ENTRY_SIZE32
SYMENT_SIZE=SYMENT_SIZE32
RELOCENT_SIZE=RELOCENT_SIZE32
CLASS=ELF_CLASS32
MACHINE=EM_386
program_header_entry fix program_header_entry32
symbol fix symbol32
reloc fix reloc32
addr fix addr32
offs fix offs32
interpreter fix interpreter32

;ELF32
BASE32=0x8048000
ELF_PHEADER_ENTRY_SIZE32 = 32
SYMENT_SIZE32=16
RELOCENT_SIZE32=8
;ELF64
BASE64=0x400000
ELF_PHEADER_ENTRY_SIZE64 = 56
SYMENT_SIZE64=24
RELOCENT_SIZE64=24

;ELF constants
ELF_CLASS32=1
ELF_CLASS64=2
ET_EXEC=2
ET_DYN=3
EM_386=3
EM_X86_64=62
DT_NEEDED=1
DT_STRTAB=5
DT_SYMTAB=6
DT_STRSZ=10
DT_SYMENT=11
DT_REL=17
DT_RELSZ=18
DT_RELENT=19
DT_RELA=7
DT_RELASZ=8
DT_HASH=4  ;; <--
DT_RELAENT=9
PT_INTERP=3
PT_DYNAMIC=2
PT_LOAD=1
R_386_32=1
R_X86_64_64=1
STB_GLOBAL=1
STT_FUNCTION=2
read=4
write=2
execute=1
xo=1
wo=2
wx=3
ro=4
rx=5
;rw=6
rwx=7
;end ELF constants

define interpreter64 "/lib/ld-linux-x86-64.so.2"
define interpreter32 "/lib/ld-linux.so.2"

macro program_header {label program_header}
macro program_header_entry32 type, location, access, align, size, memsize {
 dd type
 dd OFFSETOF location, location, 0
 if type <> PT_LOAD
  dd location#.SIZE, location#.MEMSIZE
 else
  dd size, memsize
 end if
 dd access, align
}
macro end_program_header {
 .SIZE=$-program_header
 .MEMSIZE=.SIZE
}

macro program_header_entry64 type, location, access, align, size, memsize {
 dd type, access
 dq OFFSETOF location, location, 0
 if type <> PT_LOAD
  dq location#.SIZE, location#.MEMSIZE
 else
  dq size, memsize
 end if
 dq align
}

macro symbol_table {label symbol_table}
macro end_symbol_table {
 .SIZE=$-symbol_table
 .MEMSIZE=.SIZE
}
macro symbol32 name, str, bind, type {
 name = ($-symbol_table)/SYMENT_SIZE
 if str eq
  times 16 db 0
 else
  dd str, 0, 0
  db bind shl 4 + 2, 0
  dw 0
 end if
}
macro symbol64 name, str, bind, type {
 name = ($-symbol_table)/SYMENT_SIZE
 if str eq
  times 24 db 0
 else
  dd str
  db bind shl 4 + 2, 0
  dw 0
  dq 0, 0
 end if
}

macro reloc_table {label reloc_table}
macro end_reloc_table {
 .SIZE=$-reloc_table
 .MEMSIZE=.SIZE
 restore reloc_table
}
macro reloc32 label, symbol, type {dd label, symbol shl 8 + type}
macro reloc64 label, symbol, type {dq label, symbol shl 32 + type, 0}

macro string_table {label string_table}
macro string name, str {
 name=$-string_table
 if str eq
  db 0
 else
  db str, 0
 end if
}
macro end_string_table {
 .SIZE=$-string_table
 .MEMSIZE=.SIZE
}


macro addr32 [value] {dd value}
struc addr32 [value] {. dd value}
macro offs32 [value] {dd value}
struc offs32 [value] {. dd value}
macro addr64 [value] {dq value}
struc addr64 [value] {. dq value}
macro offs64 [value] {dq value}
struc offs64 [value] {. dq value}

OFFSETOF equ -BASE+
org BASE

Elf_EHdr:
db 0x7F, "ELF", CLASS, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0  ;
dw ELF_TYPE
dw MACHINE
dd 1
addr ENTRYPOINT                                         ;entrypoint
offs OFFSETOF program_header
offs 0
dd 0
dw Elf_EHdr.SIZE
dw ELF_PHEADER_ENTRY_SIZE
dw program_header.SIZE/ELF_PHEADER_ENTRY_SIZE
dw 0, 0, 0
.SIZE=$-Elf_EHdr

program_header
 program_header_entry PT_INTERP, _interpreter_name_, ro, 1
 program_header_entry PT_DYNAMIC, _dynamic_, ro, 4
 program_header_entry PT_LOAD, Elf_EHdr, rwx, 0x1000, FILE.SIZE, FILE.SIZE
end_program_header


align 4
_dynamic_ :
addr DT_NEEDED, strtab@libc
addr DT_NEEDED, strtab@gtkx11
addr DT_NEEDED, strtab@gobject
addr DT_STRTAB, string_table
addr DT_SYMTAB, symbol_table
addr DT_STRSZ, string_table.SIZE
addr DT_SYMENT, SYMENT_SIZE
addr DT_HASH, hash_table
addr DT_RELA, reloc_table
addr DT_RELASZ, reloc_table.SIZE
addr DT_RELAENT, RELOCENT_SIZE
addr 0, 0                               ;terminator
.SIZE=$-_dynamic_
.MEMSIZE=.SIZE

;; here comes the hash table
hash_table:
dd 1, 1
.bucket:
rd 1
.chain:
rd 1

string_table
 string strtab@null
 string strtab@libc, "libc.so.6"
 string strtab@printf, "printf"
 string strtab@gtk_init_check, "gtk_init_check"
 string strtab@gtk_window_new, "gtk_window_new"
 string strtab@gtk_widget_show, "gtk_widget_show"
 string strtab@gtk_main, "gtk_main"
 string strtab@gtkx11, "libgtk-x11-2.0.so.0"
 string strtab@exit, "exit"
 string strtab@gtk_main_quit, "gtk_main_quit"
 string strtab@g_signal_connect_data, "g_signal_connect_data"
 string strtab@gobject, "libgobject-2.0.so.0"
 string strtab@gtk_window_set_title, "gtk_window_set_title"
end_string_table

align 8
symbol_table
 symbol symtab@null
 symbol symtab@printf, strtab@printf, STB_GLOBAL, STT_FUNCTION
 symbol symtab@gtk_init_check, strtab@gtk_init_check, STB_GLOBAL, STT_FUNCTION
 symbol symtab@gtk_window_new, strtab@gtk_window_new, STB_GLOBAL, STT_FUNCTION
 symbol symtab@gtk_widget_show, strtab@gtk_widget_show, STB_GLOBAL, STT_FUNCTION
 symbol symtab@gtk_main, strtab@gtk_main, STB_GLOBAL, STT_FUNCTION
 symbol symtab@exit, strtab@exit, STB_GLOBAL, STT_FUNCTION
 symbol symtab@gtk_main_quit, strtab@gtk_main_quit, STB_GLOBAL, STT_FUNCTION
 symbol symtab@g_signal_connect_data, strtab@g_signal_connect_data, STB_GLOBAL, STT_FUNCTION
 symbol symtab@gtk_window_set_title, strtab@gtk_window_set_title, STB_GLOBAL, STT_FUNCTION
end_symbol_table

align 8
reloc_table
 reloc _printf_, symtab@printf, R_386_32
 reloc _gtk_init_check_, symtab@gtk_init_check, R_386_32
 reloc _gtk_window_new_, symtab@gtk_window_new, R_386_32
 reloc _gtk_widget_show_, symtab@gtk_widget_show, R_386_32
 reloc _gtk_main_, symtab@gtk_main, R_386_32
 reloc _exit_, symtab@exit, R_386_32
 reloc _gtk_main_quit_, symtab@gtk_main_quit, R_386_32
 reloc _g_signal_connect_data_, symtab@g_signal_connect_data, R_386_32
 reloc _gtk_window_set_title_, symtab@gtk_window_set_title, R_386_32
end_reloc_table

_interpreter_name_ db interpreter, 0
.SIZE=$-_interpreter_name_
.MEMSIZE=.SIZE

start:
        lea     eax, [esp]
        lea     ecx, [esp+4]
        push    ecx
        lea     ecx, [esp]
        push    ecx eax
        call    [_gtk_init_check_]
        add     esp, 8+4
        test    eax, eax
        jz      _error_init_gtk

        push    0
        call    [_gtk_window_new_]
        pop     ecx
        mov     ebx, eax

        xor     eax, eax
        push    eax eax eax destroy_handler signame_destroy ebx
        call    [_g_signal_connect_data_]
        add     esp, 24

        push    app_title ebx
        call    [_gtk_window_set_title_]
        add     esp, 8

        push    ebx
        call    [_gtk_widget_show_]
        pop     ecx

        call    [_gtk_main_]
        jmp     _exit

_error_init_gtk:
        xor     eax, eax
        push    msg_error_gtk_init_fail
        call    [_printf_]
        pop     eax
_exit:
        xor     eax, eax
        push    eax
        call    [_exit_]

destroy_handler:
        call    [_gtk_main_quit_]
        ret

msg_error_gtk_init_fail db "GTK+ Initialization fails!", 10, 0
app_title db "GTK+ from scratch", 0
signame_destroy db "destroy", 0

align 4
_printf_ addr ?
_gtk_init_check_ addr ?
_gtk_window_new_ addr ?
_gtk_widget_show_ addr ?
_gtk_main_ addr ?
_gtk_main_quit_ addr ?
_g_signal_connect_data_ addr ?
_gtk_window_set_title_ addr ?
_exit_ addr ?

FILE.SIZE=$-BASE

gives me:

Quote:

andLinux:/mnt/e# ./testelf
Inconsistency detected by ld.so: dynamic-link.h: 163: elf_get_dynamic_info: Assertion `info[9]->d_un.d_val == sizeof (Elf32_Rela)' failed!

14 Oct 2007, 11:20

nocona

Joined: 04 Aug 2007
Posts: 35

nocona 16 Oct 2007, 04:07

change line

Code:

addr DT_RELA, reloc_table 
addr DT_RELASZ, reloc_table.SIZE

Code:

addr DT_REL, reloc_table 
addr DT_RELSZ, reloc_table.SIZE

as i said before, x86 use DT_REL type.

16 Oct 2007, 04:07

snify

Joined: 02 Dec 2004
Posts: 39

snify 16 Oct 2007, 07:55

now it gives Segmentation Fault. whatever, thanks Smile

16 Oct 2007, 07:55

nocona

Joined: 04 Aug 2007
Posts: 35

nocona 27 Oct 2007, 03:37

could u please provide some info on where it segfault? it's in ld.so code or the program itself? i ran it on my system with glibc-2.4 installed and it execute fine.

27 Oct 2007, 03:37

Raedwulf

Joined: 13 Jul 2005
Posts: 375
Location: United Kingdom

Raedwulf 06 Nov 2007, 21:24

<Ooops post deleted> found your shared library sample Razz

.

Edit: Maybe show an example using a proper hash table for exported symbols?

Last edited by Raedwulf on 07 Nov 2007, 14:18; edited 2 times in total

06 Nov 2007, 21:24

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 07 Nov 2007, 06:48

nocona: wow, OOP called from assembly, this is pretty cool hack.

by the way, you could assign nicer local names to decorated method names, like "QWidget.setVisible" etc...

07 Nov 2007, 06:48

Raedwulf

Joined: 13 Jul 2005
Posts: 375
Location: United Kingdom

Raedwulf 07 Nov 2007, 07:55

Yea that would be even cooler Smile

All I can say is once Tomasz wakes up, he should take a look at this elf from scratch Smile

07 Nov 2007, 07:55

nocona

Joined: 04 Aug 2007
Posts: 35

nocona 08 Nov 2007, 06:13

Quote:

Maybe show an example using a proper hash table for exported symbols?

i didn't really quite understand ur question. that was a proper hash table, otherwise linker couldn't find any symbols from the shared library. maybe you means a macro that create hash table automatically?

thanks vid..i actually don't have any needs to use these libraries and that time I want to know how it is possible to call C++ libraries (e.g qt) from asm source.. it is strictly for my learning purpose so i just leave the name that way Smile

.

btw.. i tested the 32-bit example in my PCBSD installation and it run without modification (no need for brandelf -f linux!). it seems the loader knows about linux binary just by looking the interpreter name.. also if we want to use bsd dynamic linker, we need to change the interpreter name to /libexec/ld-elf.so.1.. not just that, we need to define 2 symbols ( i think) "environ" and "__progname" because libc imported it and it seems every bsd program define them.. so we need proper hash table here also.. next time i will put the example source for BSD.. but not here of course Wink

08 Nov 2007, 06:13

Raedwulf

Joined: 13 Jul 2005
Posts: 375
Location: United Kingdom

Raedwulf 08 Nov 2007, 08:43

Yea I meant a hash table with some macro magic Wink

.

Oh yea just to note:
define interpreter64 "/lib/ld-linux-x86-64.so.2"

There's sometimes no link between that and "/lib64/ld-linux-x86-64.so.2" so it may not run on some systems - as I've discovered Smile

.
Better use lib64.

There's also an extra DT_RPATH which is useful for specifying library paths.

e.g.

Code:

rpath fix rpath64 ; or rpath32
define rpath64 ".:/lib64:/usr/lib64:/usr/local/lib64"
define rpath32 ".:/lib:/usr/lib:/usr/local/lib"

_dynamic_ :
addr DT_RPATH, strtab@rpath
.....
.....
addr 0, 0                               ;terminator
.SIZE=$-_dynamic_
.MEMSIZE=.SIZE

string_table
 string strtab@null
 string strtab@rpath, rpath ; HERE
....
....
end_string_table

Otherwise the binary can't find a linked .so in the same path as the file (or so i've discovered on my test system (University of York Slackware 12.0)).

_________________
Raedwulf

08 Nov 2007, 08:43

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