ARM Darwin assembly -- looking for system calls (tutorial perhaps) [closed] - iphone

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So I took up assembly programming. It's quite simple on my Ubuntu box: using NASMamd GNU ld, I were able to write more or less complicated HelloWorld-style programs in half an hour.
But when it comes to the iPhone, it's so complicated. First of all, I have a JB'en iPhone 3G on 4.2.1 firmware, which means that I use the ARM port of the Darwin kernel v10.
Second. I have to use GNU as, as there's no NASM for iPhone: the native toolchain (both Xcode on Mac OS X and the opensource tooolchain on linux) use GCC.
So I have gathered together basic info about:
- how to write assembly in GNU as language;
- what are the basic ARM instructions, registers, memory access.
But even HelloWorld requires kernel calls for writing to stdout. My question is: what kernel call to use and how (what arguments go where); I should use the swi # ARM instruction, shouldn't I?
So, can you please post some info/links to tutorials, or somebody with an ARM Darwin Hello world asm code?
As of now, I could do this:
;Hello World for Linux and NASM
section data
hello db "Hello World"
helloLen equ $ - hello
section text
global _start
_start:
mov eax, 4 ; sys_write
mov ebx, 1 ; to stdout
mov ecx, hello ; address of string
mov edx, helloLen ; value (because of eq!!!) of strLen
int 0x80 ; call awesome Linux kernel
mov eax, 1 ; sys_exit
mov ebx, 0 ; "return 0; " if you like C
int 0x80 ; call kernel to end program
on ARM, however, I could only do like this:
.text
start:
mov r0, #0
mov r1, #234
add r2, r0, r1
#all mov and add and other stuff works fine
swi #0xc00
#all that I get is Bad system call error
So, anybody please?

Answer 1

Here's how libc (libSystem) does it:
; ssize_t read(int, void *, size_t)
EXPORT _read
_read
MOV R12, #3 ; SYS_read
SVC 0x80 ; 'А' ; do a syscall
BCC _ok ; carry clear = no error
LDR R12, =(cerror_ptr - . - 8) ; otherwise call error handler
LDR R12, [PC,R12] ; load pointer
B _call_error
DCD cerror_ptr - .
_call_error
BX R12 ; cerror ; jump to it (error number is in R0)
_ok
BX LR ; return to caller
; End of function _read
I.e.:
System call number is in R12 (see sys/syscall.h).
System call instruction is SVC 0x80 (SWI 0x80).
Other parameters are according to the ABI (R0-R3, then stack).
On error, carry flag is set and error number is returned in R0.

Answer 2

Best I can find right quick and yea I realize the initial post is old
http://blog.softboysxp.com/post/7888230192/a-minimal-168-byte-mach-o-arm-executable-for-ios
.text
.globl start
start:
mov r2, #14
adr r1, hello_str
mov r0, #1
mov r12, #4
swi 0x80
mov r0, #0
mov r12, #1
swi 0x80
hello_str:
.ascii "Hello, World!\n"
compile:
as new.asm -o new.o
ld new.o -o new
./new