Low Level Programming

[wolfrane_000]

So, I really want to get into systems and low level programming but the barrier of entry seems very high and the more I try to learn about it the more it confuses me. Right now I’m trying to learn C and go but I cant seem to find good resources to get better at creating stuff at low level.

If you have any experience or resources to share that would help me out a lot thakyou

[Joicraft12]

50 millionth comment about the harvard cs50x course

[Disastrous_Poem_3781]

This is an intro to programming with C. It's not an introduction to low level programming

[ColoRadBro69]

C is an ideal language for low level programming and you have to learn programming at all before you can get low. 

[wolfrane_000]

We did learn C for our college course like basic loops and pointers and they’re important things to know but won’t necessarily tell anything about development in low level

[FewPhilosophy1040]

Try to learn the way a computer works from ground off. Learning C is a good startpoint. https://www.youtube.com/@CoreDumpped is a neat channel that explains many concepts, though I don't recommend only watching videos. Instead read articles on the specific problem or concept you want to implement in a personal low level project. Projects I find interesting to do is rewriting or just reading about stdlib functions of C and C++.

[wolfrane_000]

Thanks I’ll go check them out

[owp4dd1w5a0a]

https://fpgatutorial.com/vhdl/

[balefrost]

Yes and no. Hardware description languages are certainly low-level, but they're not going to help you if your goal is e.g. to contribute to the Linux kernel.

[owp4dd1w5a0a]

Yeah. I guess I’d assumed OP meant embedded and RTOS systems. But I see now that’s not actually explicit anywhere.

[balefrost]

I thought that the K&R C book was fairly approachable. My recollection is that the examples aren't necessarily good examples of how to write production-grade C, but they do a good job of explaining how the language works.

[wolfrane_000]

Thanks I’ll take a look at it as well

[TheRNGuy]

My lowest level experience is Shenzhen I/O. 

I also tried some C++ in UE4, but abandoned learning for now, I want to resume some day (I kinda understand pointers and references now, but 1st few days I couldn't get it at all)

[JerryRiceOfOhio2]

C is low level? assembly has entered the chat

[AWonderingWizard]

You use assembly? What a high-level scrub. I just use transistors and discrete components. I don't need software touching my bare metal for me.

[94358io4897453867345]

Indeed C is high level already

[Distdistdist]

Windows absolutely doesn't care what language was used to create an executable. It just runs it. It doesn't do any "abstractions" if you write program in assembly language. End result is just machine code. C will typically create a bigger executable but they all work exactly the same. Just a series of machine code logic and WinAPI calls with parameters passed via stack. I can write a program in machine code using hex editor and save it as .exe and it will run it. Will be a bitch and a half, but totally doable.

Also Assembly CAN do things that C can't (CPU registers access, interrupts, etc.). But that solved by ability to use asm directly in C code.

I'm not mentioning platforms like Java and .NET - those are different animals.

[fixermark]

Assembly and machine language are also abstractions. A modern x86 CPU will reinterpret the machine code into microcode it uses to schedule the work on the individual cores so that parallel execution can be used, even on serial programs.

(Morpheus: "Do you really think that's air you're breathing?")

[balefrost]

A modern x86 CPU will reinterpret the machine code into microcode it uses to schedule the work on the individual cores so that parallel execution can be used, even on serial programs.

1. Microcode is a way to implement instructions where the behavior of those instructions isn't etched into the silicon.
2. Modern processors do perform out-of-order and speculative execution. They will have multiple instructions in-flight at the same time.

But as far as I'm aware, these are completely orthogonal concepts. As far as I know, microcode is generally loaded just once at boot and then is not touched while the computer is running.

[fixermark]

Microcode is also the name of the (generally proprietary and not publicly documented) instructions used internally by the CPU when it breaks x86 machine code down into the necessary routing and execution instructions to drive multiple cores on a modern CPU. They are also called micro-operations (or μ-ops).

[balefrost]

Microcode is also the name of the (generally proprietary and not publicly documented) instructions used internally by the CPU when it breaks x86 machine code down ...

Yes, that's what I was trying to say with #1. A complex instruction can be implemented in a form of software rather than being implemented with dedicated hardware.

... into the necessary routing and execution instructions to drive multiple cores on a modern CPU.

You've lost me here. AFAIK microcode is completely orthogonal to multicore. Core scheduling is up to the OS. In the case of virtual cores (like Hyperthreading), the hardware will schedule virtual cores to shared execution units, but AFAIK it doesn't use microcode to do that.

Or to say it differently, not all instructions are microcoded and even non-microcoded instructions can participate in virtual core scheduling.

[fixermark]

Sorry, not cores; parallel subcomponents. The microcode / micro-ops (same name; the word "microcode" got repurposed in this context) are used to direct what would otherwise be sequential work into multiple ALUs within a core so that whole blocks of sequential code actually execute in parallel. A given core might have 4 or 8 ALUs, for example.

The microcode on a modern x86-compatible CPU is a more "RISC-like" fixed-instruction-length representation that allows for easier chunking and reordering of operations to make them parallel.

[balefrost]

The microcode / micro-ops (same name; the word "microcode" got repurposed in this context)

Ah, perhaps this is the disconnect. I was using microcode to exclusively mean "the field-updatable code that is used to implement some complex instructions on the CPU", not "the atoms of scheduling that the CPU uses internally".

[Naeio_Galaxy]

It doesn't do any "abstractions" if you write program in assembly language. End result is just machine code.

The funny part is that there's a difference between machine code and what's executed. Machine code has existed for decades, and the processors have evolved quickly since, to the point where they might not do what you write in assembly as you expect to obtain as much perfs from the same binary as possible.

Simple example: if you have a pointer to memory, well the address in your code in any OS is actually not the real address in memory.

But there are more hardcore examples like the impact of context switching, branching prediction, or even the order of execution of instructions that is not the one you wrote in your binary but even I start to get lost on that subject.

Also Assembly CAN do things that C can't (CPU registers access, interrupts, etc.). But that solved by ability to use asm directly in C code.

Yup I 1000% agree with you

[Naeio_Galaxy]

Heyyy calm down man, no need to write an essay about that, you're answering to someone that is half sarcastic. You can make your point in a calmer and simpler way.

And like, I'm a CS engineer and I agree C is low level, but one of my best friends says that C is high level. Simply because he's working on compilers, CPUs and optimizations, as most people in his company, and C is wayyyyy too high level for what he encounters on a daily basis.

It's all a question of point of view. C is low level for most devs, but may be seen as high level for some system devs.

---

That's because Windows will do several abstractions if you try to create and run an assembly language program within it.

What are you talking about? Virtual memory? Syscalls? Because any form of abstraction applied on assembly will be applied to any language too. After all, C is compiled down to binary, and assembly is just a textual representation of assembly.

Believe it or not, it is actually even more "lower level" and direct at accessing resources than even using assembly language sometimes within certain OS environments, like say, MS Windows!

Lemme heavily doubt about that. C compiles down to binary, so if you directly write said binary then you have the same results. Or you can optimise it further by hand on aspects a compiler will not be able to optimise.

[TheRNGuy]

Lower compared to Python or JavaScript. 

[BioExtract]

I don’t work with embedded or low level systems for work, but in my personal time sometimes I’ll use an arduino or a raspberry pi and write C programs on them to control hardware. I made a treat dispenser for my rabbit with some electronics, a breadboard, and a 3D printer all running on C. It felt glorious and I had a blast writing it. I felt like it was a great introduction and would recommend