So, here is the (IMHO) much more clean 64-bit “Hello world”. what OS X contributes to the mix is that you have to add 0x20000000 to the syscall number (still have to figure out why).the call is done via the syscall instruction.arguments are passed on the registers rdi, rsi, rdx, r10, r8 and r9.Jump to section A.2.1 for the syscall calling convention. 32Ħ4-bit is a bit cleaner, but completely different: OS X (and GNU/Linux and everyone except Windows) on 64 architectures adopt the System V AMD64 ABI reference. set the eax register to the write syscall number (4).align the stack by moving the stack pointer 4 more bytes (16 - 4 * 3).push the stdout file descriptor (1) to the stack.push a pointer to the string to the stack.push the length of the string ( int) to the stack.So what we have to do to print a “Hello world” is: arguments passed on the stack, pushed right-to-left.I’m on a Intel machine, so what we are looking for is the x86 syscall calling conventions for the OS X or BSD platform. Compile with nasm or yasm, output format MachO, and link with ld. A cute 32-bit program, written in NASM assembler language. So, to write our proverbial Hello world we will pick the syscall 4 4 AUE_NULL ALL The header also hints at the fact that they are inherited from BSD. The system callsįirst, we need to know what system call we want to make, and what arguments it pretends.Ī full list is hosted by Apple here.

Usually, these are wrapped by C functions in the standard library. Recently my main dev machine is a MacBook running OS X, so it felt reasonable to fiddle with making system calls of that platform.īy the way, a system call is a function of the kernel invoked by a userspace program and it can be something like writing to a file descriptor, or even exiting. The next step in my playing with chroot escapes is crafting some shellcode.

Assembly language on mac