Signals. I spent 2 years to understand this part.

A quick introduction to one of the interprocess communication mechanisms in linux.

00:00 Main idea. We want to execute a function when external signal arrives
00:50 While loop. We can't simply jump to the signal handler!
01:24 Interrupts. Breaking a natural instruction flow
02:30 Saving registers. Kernel preserves user register values
03:09 How pc is saved
04:03 The most important idea! Replacing the pc
04:40 Big Picture overview.
05:55 To the Source code!
07:16 Kernel entry. Disassembling my kernel binary
12:04 Replacing the program counter
12:35 Return to user.
13:28 Signal handler is finished. How to resume the main code?
14:14 How the stack works when enter the kernel
16:26 We need to keep main code's original registers!
16:49 Kernel stack has to be empty. Overflow. Nested signals
17:30 Saving original regs to user stack
18:48 Kernel trampoline. Sigreturn
20:45 Bonus! (about the compiler bug video)

[saaah]

What a time to be alive, when videos like this exist

[CFSworks]

I did a double-take when I saw the AArch64 assembly... most YouTubers go straight to x86/x64 when talking about assembly, even though it's really not as beginner-friendly as RISC sets, so it's a breath of fresh air seeing someone introducing beginners to ARM. :)

[senyai]

It looks like my process miss a signal every now and then. After watching this video, I think the issue is on my side, but I triple checked all the code. What a life.

[MrOnlineCoder]

So many high quality low level educational videos are being recommended nowadays, your is definitely one of them! I really like the "raw" work with objdump disassembly

[vladimirvparfenov]

6:15 what i liked— what i LOVED about this succinct, anthropomorphic explanation is that it really helped frame for me (a software engineer) how to think about the contractual interface i have with the hardware engineers without having to know about the details of CPU architecture.

overall just TERRIFIC presentation and formatting.

[artsmadeit]

I swear this channel will blow up someday. I really like the chosen topics and presentation on this channel.

[yugshende]

I cant even imagine what it must be like to "map" the kernel code in your brain because your explanation here was spot on. I have always (ie almost 6 years in SDe industry and 6 years of education before that) at a very high level just "assumed" that signals and interrupts are a thing and I know for a fact that I cannot dive into Kernel code to save my life but this video explanation I can definitely say I understood everything. That's definitely a kudos to you sir. I wish to understand more low level systems stuff more in detail as I continue my journey.

[TheMoucastre]

Your videos, explanations, animations, are all absolutely stellar. So clear, so efficient. PLEASE keep sharing the knowledge, this is truly remarkable.

[jomeow-vifx]

the video's quality and information are truly stunning

[dshindov]

Great video! I like your choice to explain everything with ARM assembly, instead of x86. You earned a new subscriber :)

[zokalyx]

I will watch this again in like 6 months and go "ooohhh"

(actually, I already understood like 75% of the video without knowing a single thing about signals, just gotta get that remaining 25%)

[umarfaruk]

just saw the words 2 years and i clicked and subscribed. Knowledge takes time and effort. This title clearly says it too <3

[spazzels]

It's like I didn't understand anything but still watched it, thanks for the video

[Ab_Irato]

The layout is just beautiful and the instructions are crystal clear.

[AK-vxdy]

Very nice teaching method, by resolving problems one by one. Great video !!!
Respect to the knowledge level. I don't know if many of us will need it daily, but i hope many of us who want to know how it is done inside, will gather to such
level that you will keep sharing your wisodm with us.

[jay-gj]

What a great video! I love these low level stuff! I actually did not realize that signal is so complicated(for me) until I see this video. Thank you a lot for making such a high quality video to describe signals in detail! It is easy to understand and the visualization is intuitive!

[haiphamle]

Excellent content! I hope your channel receiving more attention.

[kovsi_]

Your channel is so good! Outstanding! Keep up the good work.

[Spitfire]

I find it amazing that every time an interrupt happens the CPU does this and it’s still able to be so performant.

[DavidAlsh]

Wow great timing, this is literally exactly what I am battling with at the moment.