Hello World on FreeBSD

Index > Unix > Hello World on FreeBSD

Author

Thread

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 19 Nov 2006, 14:10

What's wrong here?

Code:

$ uname -vmp
FreeBSD 6.1-RELEASE #0: Sun May  7 04:32:43 UTC 2006     root@opus.cse.buffalo.e
du:/usr/obj/usr/src/sys/GENERIC  i386 i386
$ cat hello-exe.asm
format ELF executable
entry main

main:
push    mensaje.size
push    mensaje
push    1               ; stdout
mov     eax, 4          ; sys_write
push    0               ; dummy argument
int     $80

xor     eax, eax        ; sys_exit
int     $80

mensaje         db      "Hello World ", 10
mensaje.size    =       $-mensaje
$ ./fasm hello-exe.asm
flat assembler  version 1.67.14  (16384 kilobytes memory)
3 passes, 121 bytes.
$ chmod +x hello-exe
$ ./hello-exe
ELF binary type "0" not known.
./hello-exe: 1: Syntax error: "(" unexpected
$ file hello-exe
hello-exe: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically
linked, stripped
$

Note that producing an ELF object first and then using gcc to produce the executable works fine

Code:

$ uname -vmp
FreeBSD 6.1-RELEASE #0: Sun May  7 04:32:43 UTC 2006     root@opus.cse.buffalo.e
du:/usr/obj/usr/src/sys/GENERIC  i386 i386
$ cat hello.asm
format ELF
public main

main:
push    mensaje.size
push    mensaje
push    1               ; stdout
mov     eax, 4          ; sys_write
push    0               ; dummy argument
int     $80

xor     eax, eax        ; sys_exit
int     $80

mensaje         db      "Hello World ", 10
mensaje.size    =       $-mensaje
$ ./fasm hello.asm
flat assembler  version 1.67.14  (16384 kilobytes memory)
3 passes, 377 bytes.
$ gcc hello.o -o hello
$ ./hello
Hello World :D
$ file hello
hello: ELF 32-bit LSB executable, Intel 80386, version 1 (FreeBSD), dynamically
linked (uses shared libs), not stripped
$ file hello.o
hello.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped
$

Is the last one method the unique available to produce executables for FreeBSD?

19 Nov 2006, 14:10

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 19 Nov 2006, 15:25

Perhaps you need to use the "brandelf -t FreeBSD" command, or something like?

19 Nov 2006, 15:25

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 19 Nov 2006, 15:49

Code:

$ brandelf -t FreeBSD hello-exe                                                
$ file hello-exe                                                               
hello-exe: ELF 32-bit LSB executable, Intel 80386, version 1 (FreeBSD), statica
ly linked, stripped                                                            
$ ./hello-exe                                                                  
Hello World :D                                                                 
$

Thanks!!

BTW, this utility just sets "FreeBSD" and doesn't do anything else? If it is the case then it could be great to add some feature in fasm to override the SYSV built-in default (but doing it inside the source, not a comand line parameter, something like "abi FreeBSD" or "abi number").

[edit] Or maybe better, something like "format ELF {FreeBSD|SYSV|number|etc} executable " / "format ELF {FreeBSD|SYSV|number|etc}"[/edit]

19 Nov 2006, 15:49

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 19 Nov 2006, 16:30

Well, it was already requested: http://board.flatassembler.net/topic.php?t=6163
I certainly should consider this.

19 Nov 2006, 16:30

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 19 Nov 2006, 18:09

Thanks for consider this Smile

19 Nov 2006, 18:09

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 30 Nov 2006, 21:23

Code:

$ brandelf -t Linux hello-exe
$ file hello-exe                                                               
hello-exe: ELF 32-bit LSB executable, Intel 80386, version 1 (GNU/Linux), statically linked, stripped
$ ./hello-exe
Segmentation fault (core dumped)

Now I see why the Linux examples doesn't work in FreeBSD, because fasm produces SYSV executables instead. Is there some difference between Unix SysV ABI and Linux ABI or just FreeBSD is too strict?

PS: Note that the Segmentation fault is OK since the way I'm calling the kernel is for FreeBSD (I'm using the same source from the first post).
PS2: And I have Linux ABI compatibility enabled of course

30 Nov 2006, 21:23

crc

Joined: 21 Jun 2003
Posts: 637
Location: Penndel, PA [USA]

crc 02 Dec 2006, 04:58

The Linux ABI is different. The BSDs (at least on 32-bit) pass arguments to syscalls via the stack, where Linux uses registers. I believe that at least some of the function numbers differ as well.

FreeBSD does support the Linux ABI, but if you brand a FreeBSD executable as "Linux", it will try to run it with the Linux ABI and have problems quickly.

As a side note, not all BSD's make use of branding. NetBSD for example checks for a ".note.netbsd.ident" section for branding information, rather than use a "brandelf" type tool. Given this, it is possible to make a program that works on both FreeBSD (after branding) and NetBSD (no branding needed if this section exists with the proper values).

02 Dec 2006, 04:58

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 02 Dec 2006, 14:16

crc, yes, I know that Linux ABI is different to FreeBSD ABI. My question was

Quote:

Is there some difference between Unix SysV ABI and Linux ABI or it is just FreeBSD that is too much strict? bold=corrections

Thanks for the note about NetBSD, now we know that http://board.flatassembler.net/topic.php?t=6163 is not enough (if fasm just brands the executable instead of adding a note when found NetBSD)

PD: Not that by strict I mean that FreeBSD refuses to execute SYSV executables when the same executables works on Linux with "SYSV" brand and "Linux" brand.

02 Dec 2006, 14:16

hamoz

Joined: 14 Dec 2006
Posts: 29

hamoz 20 Feb 2007, 18:26

LocoDelAssembly, that is your hello world example

I didnt use gcc to link the hello coz the current fasm gave me an

executable file no hello.o < no object file Confused

> it works well after I have

been allowed it as a root

Quote:

# ./fasm hello.asm
flat assembler version 1.67.21 (16384 kilobytes memory)
3 passes, 129 bytes.
# brandelf -t freebsd hello
# ./hello
./hello: Permission denied.
#chmod 777 hello
#./hello
hello world very happy
# file hello
hello: ELF 32-bit LSB executable, Intel 80386, version 1 (FreeBSD), statically linked, stripped

tell me why I didnt need to gcc is it an advantage in the current fasm

because the fasm is linked by gcc first time and we dont need it again

I did it easily than yours

thanks alot Smile

20 Feb 2007, 18:26

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 20 Feb 2007, 23:09

Not sure if you are asking or not Razz

You don't need gcc for your files assembled with fasm because since you have specified "format ELF executable" it produces an executable and for that reason no linking is needed but a branding is required since fasm brands the executable as SysV and that doesn't work.

20 Feb 2007, 23:09

hamoz

Joined: 14 Dec 2006
Posts: 29

hamoz 20 Feb 2007, 23:35

exactly I have been specified " format ELF executable "

but one question what does the brandelf command brand to if it is not

SYSV.... Very Happy

20 Feb 2007, 23:35

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 21 Feb 2007, 00:17

The branding specifies which type of ABI (Application Binary Interfase) the executable has, for example FreeBSD supports Linux executables so if you brand it as Linux, FreeBSD will execute it but since the kernel on FreeBSD is called different than Linux the executable will produce errors at runtime (The parameters on FreeBSD system call are passed in stack but on Linux are passed with registers).

21 Feb 2007, 00:17

hamoz

Joined: 14 Dec 2006
Posts: 29

hamoz 21 Feb 2007, 00:24

LocoDelAssembly, I really thank you so much Smile

cheers

newbie

21 Feb 2007, 00:24

jb

Joined: 26 Mar 2007
Posts: 5
Location: Holland

jb 26 Mar 2007, 23:23

I have a small patch for fasm to create an elf note for NetBSD 3.1/i386 executables. It allows a new flag (`note') in the segment directive. Here's a small example of how to use it:

$ cat test.asm
format elf executable
entry start
start:
push 47
push eax
xor eax,eax
inc eax
int 0x80
include 'note.inc'
$ cat note.inc
segment note
dd 0x00000007
dd 0x00000004
dd 0x00000001
dd 0x4274654e
dd 0x00004453
dd 0x11f0e540
$ fasm test.asm
flat assembler version 1.67.21 (16384 kilobytes memory)
3 passes, 148 bytes.
$ file test
test: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for NetBSD 3.1, statically linked, stripped
$ ./test; echo $?
47
$ readelf -l test

Elf file type is EXEC (Executable file)
Entry point 0x8048074
There are 2 program headers, starting at offset 52

Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x000074 0x08048074 0x08048074 0x00008 0x00008 RWE 0x1000
NOTE 0x00007c 0x0804907c 0x0804907c 0x00018 0x00018 0x4

To keep `file' accurate the alignment was changed from 4K to 4. RWE is a don't care.

The note itself was created by picking a random executable (i.e. /bin/ls), looking at the segment header for the note to get offset and size (0x00018=24 bytes), and then doing a hexdump -e '6/4 "dd 0x%08x\n"' -n 24 -s 0x108 on /bin/ls.

Here's the patch:

$ rcsdiff -r1.1 -rnote formats.inc
===================================================================
RCS file: formats.inc,v
retrieving revision 1.1
retrieving revision 1.2
diff -r1.1 -r1.2
3630a3631,3632
> cmp ah,4
> je elf_note
3643a3646,3649
> elf_note:
> mov byte [ebx],4
> mov word [ebx+1Ch],4
> jmp elf_segment_flags
$ rcsdiff -r1.1 -rnote tables.inc
===================================================================
RCS file: tables.inc,v
retrieving revision 1.1
retrieving revision 1.2
diff -r1.1 -r1.2
273a274
> db 'note',19h,32

Crude, but effective.

26 Mar 2007, 23:23

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 13 Jul 2010, 23:41

Well, I can't remember how I managed to copy the text from the VirtualPC (or maybe changed the copy behavior in some version?), so I'll have to post a screenshot instead...

It is essentially the same code I posted at the beginning of this thread but now the linker nor brandelf are needed anymore (due to the latest changes in the ELF formatter)

PS: Notice the "9" in the first line of the code, that is the value for FreeBSD ABI.

Description:
Filesize:	13.02 KB
Viewed:	24537 Time(s)

13 Jul 2010, 23:41

< Last Thread | Next Thread >

Forum Rules:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum