Would executable files be Machine Code - made for the hardware?

Question

Here is from Wiki .

"In computing, an executable file causes a computer "to perform indicated tasks according to encoded instructions," ( Machine Code ?? )

"Modern operating systems retain control over the computer's resources, requiring that individual programs make system calls to access privileged resources. Since each operating system family features its own system call architecture, executable files are generally tied to specific operating systems."

Well this is my perspective . Executables cannot be Machine Code as they need to tal to the OS for hardware services ( system calls) Hence executable is just not yet "Machine Code" ... Perhaps it is like some part of the code is actual Machine Code and some parts are just meant to call the Machine code embedded in the Operating system ? Overall it contains some junks of Machine Code - and some junks of codes to call the operating system .

Edited after Damon's Answer : In the end OS is a set of machine codes . Basically OS would be doing the job of copy pasting user's Machine Code ( created by C Compiler ) and then if the instruction is a system call , the transfer goes to OS memory region for handling it . Now the question is what Machine Code generated in C can do this part ? Like asking to transfer control to OS etc - I suppose its system calls at higher abstraction but under the hood - how does it work .

I get a feeling its similar to chicken egg problem , C creates OS and C uses OS Cant find the exactly how the process goes . Can anyone break the puzzle for me ?

Answer 1

One thing does not exclude the other. Executables are (unless they are some form of bytecode running in a virtual machine) machine code. However, there are different kinds of instructions, some of which are not usable at certain privilegue levels.

That is where the operating system comes in, it is "machine code" that runs at the highest privilegue level, working as arbiter for the "important" parts and tasks, such as deciding who gets CPU time and what value goes into some hardware register.

(originally comment, made an answer by request)

EDIT: About your extended question, this works approximately as follows. When the computer is turned on, the processor runs at its highest privilegue level. In this "mode", the BIOS, the boot loader, and the operating system can do just what they want. This sounds great, but you don't want any kind of code being able to do just whatever it wants.

For example, the code can tell the MMU which memory pages are allowed to be read or written to, and which ones are not. Or, it can define what address is called if "something special" such as a trap or interrupt happens. Or, it can directly write to some special memory addresses that map ports of some devices (disk, network, whatever).

Eventually, the OS switches to "unprivileged" mode and calls some non-OS code. When a trap or interrupt happens, execution is interrupted and continues elsewhere (as specified by the OS previously), and the privilege level is upped again. Once the interrupt has been dealt with, privilege is taken away, and user code is called again.
If a user program needs the OS to do something "OS like", it sets up parameters according to an agreed scheme (for example in some particular registers) and executes a trap instruction.

This is for example how things like multithreading or virtual memory are implemented. In regular intervals, a timer fires off an interrupt, which stops execution of "normal" code, and calls some code in the kernel (in privileged mode). That code then decides what user process control should returned to, after some kind of priority scheme. Those are the "CPU time slices" that are handed out. If some process reads from or writes to a page that it isn't allowed, a trap is generated by the MMU. The OS then looks at what happened and where, and decides whether to load some data from disk into some memory region (and possibly purge something else) and change the process' mappings, or whether to kill the process with a "segmentation fault" error.

Of course in reality, it is a million times more complicated, but in principle that's about as it works.

It does not really matter whether the OS or the programs were originally written in C or with an assembler. To the processor, it's just a sequence of machine instructions. Even a python or perl script is "just machine instructions" in the end, only with a detour via the interpreter.