hello world using fasm (arm) for android

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sleepsleep

Joined: 05 Oct 2006
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sleepsleep

if there are a guide on, how to do hello world using fasm (arm) for android, maybe kinda cool,

09 May 2014, 06:47

typedef

Joined: 25 Jul 2010
Posts: 2913
Location: 0x77760000

typedef

sleepsleep wrote:

if there are a guide on, how to do hello world using fasm (arm) for android, maybe kinda cool,

Compile with FASMARM (1.71.13)

Code:

        format ELF executable
        entry start

        segment readable executable

start:
        mov     r0, 1
        mov     r1, hello
        mov     r2, len
        mov     r7, 4 ; sys_write
        svc     0
    
        mov     r0, 1
        mov     r7, 1 ; sys_exit
        svc     0

hello:
        db      'Hello world android',10
len  =  $-hello

Using adb.exe

Code:

adb push hello_world /sbin/hello_world
adb shell chmod 777 /sbin/hello_world
adb shell /sbin/hello_world

Above code can also be included in an app and executed at run time.

NOTE: I have a rooted phone so I'm able to throw stuff in that directory.

31 May 2014, 07:46

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17484
Location: In your JS exploiting you and your system

revolution

To make the code a bit more flexible you can do this:

Code:

;...
adr r1,hello
;...

31 May 2014, 08:07

typedef

Joined: 25 Jul 2010
Posts: 2913
Location: 0x77760000

typedef

Oh. Lol, after banging my head I thought you'd moved it here.

And yup,

mov r1, hello
ldr r1, [hello]
adr r1, hello

31 May 2014, 08:24

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17484
Location: In your JS exploiting you and your system

revolution

ldr won't do it for you unless you put a pointer there.

31 May 2014, 08:26

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17484
Location: In your JS exploiting you and your system

revolution

Note that the reason I suggest using adr instead of mov is because by default fasmarm will use all available instructions from all architecture versions. So the mov will use the v7/T2 wide encoding to create "movw r1,0x8074". Whereas using adr will encode "add r1,r15,0x14" which is relocatable.

BTW: It is also advisable to use the processor and coprocessor directives to tell fasmarm which instructions are available. Without these you may get unavailable encodings for your particular CPU.

31 May 2014, 11:38

sleepsleep

ok, this is cool, and i wanna say thank you first to typedef.

31 May 2014, 17:21

Picnic

Joined: 05 May 2007
Posts: 1288
Location: behind the arc

Picnic

Hi all,

I have tested typedef's example using fasmarm and adb.exe as suggested above (day 1 in arm).
Then i try a string copy, but the code outputs nothing.

Code:

 format ELF executable
 entry start 

 segment readable executable 

start:
 mov    r1, src
 mov    r0, dest

strcopy: 
 ldrb   r2, [r1], 1
 strb   r2, [r0], 1
 tst    r2, r2
 bne    strcopy

 mov     r0, 1
 mov     r1, dest
 mov     r2, 5
 mov     r7, 4   ; write syscall
 svc     0

 mov    r0, 0  ; exit
 mov    r7, 1
 svc    0

 src    db "12345",0
 dest   db "00000",0

01 Feb 2015, 11:54

Picnic

Joined: 05 May 2007
Posts: 1288
Location: behind the arc

Picnic

I would really appreciate a hint.

01 Feb 2015, 19:22

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17484
Location: In your JS exploiting you and your system

revolution

Which system are you using? Perhaps "svc 0", or the parameters you are passing, or the file format, is the problem because the copy code appears to be fine. Also the the note above about using "adr" instead of "mov" to get your code relocatable. And use the "processor" directive to avoid any silliness with incompatible CPUs.

02 Feb 2015, 00:45

Picnic

Joined: 05 May 2007
Posts: 1288
Location: behind the arc

Picnic

Hi revolution,

I have windows xp connected with my android phone (CPU:ARM Cortex A7, GPU:ARM Mali-400 MP1) via usb cable. typedef's code along with few other tiny scripts i wrote are working, but the code above outputs "Segmentation fault" at my phone's terminal window. How to workaround this?

02 Feb 2015, 20:09

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17484
Location: In your JS exploiting you and your system

revolution

Did you try with ADR? Did you use the proper PROCESSOR setting?

03 Feb 2015, 01:07

Picnic

Joined: 05 May 2007
Posts: 1288
Location: behind the arc

Picnic

I used adr but the error remains. What can be the correct settings in my case, can you show me a processor setting example ?
I noticed that whenever i use strb i am getting a "Segmentation fault".

p.s. I appreciate the assistance.

03 Feb 2015, 07:19

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17484
Location: In your JS exploiting you and your system

revolution

Perhaps the Android system enforces the read only attribute you used?

Code:

segment readable executable

03 Feb 2015, 07:24

Picnic

Joined: 05 May 2007
Posts: 1288
Location: behind the arc

Picnic

Golden reply, thank you. Smile

I struggled enough and lost my temper for a while.

03 Feb 2015, 17:04

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