m-schmidt / HelloSilicon

An attempt with assembly on the machine we must not speak about

HelloSilicon

An attempt with assembly on the machine we must not speak about

So this is a little attempt to invoke syscalls on a machine running a Mach Kernel on an ARM64-like architecture.

The code is taken from the book Programming with 64-Bit ARM Assembly Language

What Works

The MacAs Target runs. Here, a C main calls the assembly routine _start.

What Doesn't Work

Anything without C. In the AsMain target there is a file ´main.s´, in which I renamed _start to _main. I can successfully build, and even run, but the executable crashes with an EXC_BAD_ACCESS

Trying to build the file by itself fails.

% make
as -o HelloWorld.o main.s
ld -o HelloWorld HelloWorld.o
ld: warning: arm64 function not 4-byte aligned: _main from HelloWorld.o
ld: warning: arm64 function not 4-byte aligned: helloworld from HelloWorld.o
ld: dynamic main executables must link with libSystem.dylib for architecture arm64

Adding -lSystem doesn't make it much better:

make           
as -o HelloWorld.o main.s
ld -o HelloWorld HelloWorld.o -lSystem
ld: library not found for -lSystem

Interesting:

The alignment warning only appears in the AsMain target not when the code is succesfully built.