GDB is REALLY easy! Find Bugs in Your Code with Only A Few Commands
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- Опубліковано 28 чер 2024
- Join me and learn how to debug a program written in C using GDB. In this video, we go over how to compile a program written in C so that GDB can present it, as well as the basic commands used in GDB to debug a program.
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Timestamps
Intro 0:00
Compiling Code for GDB 0:20
Starting GDB 1:27
Breakpoints 2:05
C Step vs ASM Step 2:37
Step Over vs Step In 3:26
Finding the Bug 4:26
Outro 7:16
Need more low level channels like this. Thank you!
Glad you like them!
One of the clearest, least daunting videos about GDB. I actually feel I could do it.
You can, mate, you can!
Best videos about C and embedded programming. I love the way you put motivation on the table. And I really appropriate the short length of the video and effort put into it.
I absolutely love it when I find a video for beginners and it truly is for beginners.
Thank you so much for this. Friendship ended with debug print statements, now gdb is my best friend.
Ah, gdb my old friend. We don't talk much, but when we do the conversation is invaluable. I tracked down a bug in my php code with gdb for a long lived demon process that was crashing from time to time. Running that program in gdb for a few days until it finally reproduced the error that wasn't making it to the error handler made everything so much clearer. (This was a long time ago, and there was a bug in curl that was causing it, I since moved over to using the native file_get_contents functions for http requests and the bug went away.)
Thanks a lot! Always wanted to know how to use gdb manually and this is a perfect starting point! 👍
That was a really useful succinct introduction to getting going with GDB. Thanks !
Glad it was helpful!
first time using GDB, and this video gave me the tools do everything I normally need in my IDE debugger just fine. Already fixed 2 or 3 bugs in the past few days that would've been a pain in the ass with only print debugging.
Never used gdb alone. Always with a front-end. Very interesting to see how to use it directly. thnx!
I noticed a minor mistake when you explaining the failure instruction. This is AT&T assembly syntax (not Intel) so "mov %eax, (%rdx)" means moving the value in %eax to the one referenced by (%rdx), not the other way around.
How can you tell if the code is AT&T or Intel order ?
@@BobBeatski71 the Intel syntax doesn't have "%" or "()" so that instruction would probably look like "mov rdx,eax". And you can set your GDB or objdump to show disassembly code in either syntax.
@@kkenzuro A little Googling got me the info I needed. The AT&T format of disassembly is very similar to Motorola 68K style so now reading the decode is rather more straightforward. Thanks !
Clear and very supportive explanation!
Nice, succinct and to the point! Thank you!
Thanks! This was exactly what I needed. ❤️
I subscribed
I hope you do more forensic engineering
Great tutorial, learned something new, thanks!
Great Tutorial man. Its so intresting to see the assembly code!
Thank you so much! Nice and simple :)
this is great! Thanks a lot.
This is really good quality content for beginners. I'm showing this to my classmates that struggle with gdb, and they all seem to like it too. You go straight to the point, give a good concrete example and you speak well. Thank you!
Wow. Thank you so freaking much, buddy.
Good content!!
THANK YOU!
very helpful, thank you Low Level
You're welcome!
Thank you so much, this helped me so much!!
Glad it helped!
cool man!!! gdb is really awesome. This opened my eyes and was well explained. And i think you may have solved my question about openjdk vs openjdk-devel. I suppose i could debug in gdb if i use the -devel version. But if i use IDEA i can just debug within it... that's my guess.
oh i just found out that the jdk comes with jdb debugging tool!
thank you :)
Great video - if you link the second video on GDB (mentioned in this video) - that be awesome
Excellent!
Many thanks!
Great video - I am really inspired now to discover more. I would like to debug a little assembly code program, I am running on 64bit Raspberry Pi Buster O/S. I am using these commands to assemble/compile to program: as sample.asm -o sample.o ... then gcc -g sample.o sample -nostdlib The program runs fine, but if I try to debug using gdb, it complains that no debugging symbols found in sample. What must I do to the as or gcc commands to get gdb to accept it?
Thanks for the ref trick
Great video! gdb is one of those tools I know I should know much better. Please keep this stuff coming!
You got it!
@@LowLevelLearning btw, if you start a Patreon or a UA-cam membership, I’ll definitely subscribe!
Great video that explains the main features of gdb. Unfortunately, from my experience, as soon as the code gets bigger it becomes harder and harder to use... Easier to call valgrind and put prints everywhere...
thanks
Thanks for the tutorial 🤩
should probably get back in to C in my freetime
PS: liked and subscribed
(during my university time I had one semester of C but later in job I only had/could to do Java and later PHP which was one reason I've switched to server admin 😅)
Could you create a complete series on reversing with GDB?
what do you recommend to start leaning C for a person that knows java or golang?
Thanks a lot sir , but i am having an issue with the gdb tui my cmd on windows says tui is not supported when u try to enable it
What is his linux distro or DE setup it looks so clean ?
is there a way to have a separate run path and source path?
Thanks for the great tutorial. 👍. What kind of Linux distro are you running? It looks very clean and nice.
Ubuntu 20.04 with i3, feh and compton :)
@@LowLevelLearning 🙏🙏🙏
So, both "stepping into" and "stepping over" run the code, but stepping over doesn't go line-by-line into the called function. Somehow I had missed that. I thought it may have been an instruction to ignore (as in, not run at all) that call/instruction.
What do you recommend for multi thread programs ?
Thanks
No problem
GDB is invaluable, especially for its ability to handle core dumps.
Hey, great video! I'm a noob so... How can I do that on windows? via cmd? Is it possible?
Just knowing I coded ALL these years without a debugger instantly made me 2 times older.
which commend you use to display the source code?
How do you get that pretty interface in gdb?
The explanation was simple and didactic. The audio is clear, it's helps a lot to flow of the idea.
Help me a lot for beginner in GDB, thank you !!
Glad it helped!
I have the problem that gdb just jumps over my entire while loop, I specifically want to debug this while loop and I find no way to step into the while loop which is very very frustating.
I'm using it over the Code:Blocks Gui, perhaps this is the thing causing all the issues. Code:blocks was recommended to me as a very good IDE to code C with, I still have to see the benefits, as for now it causing more issues than it solves ^^'
Cool. Can GDB debug for architectures other than the cpu is running? like ARM on a X86 cpu?
You can use gdb-multiarch on qemu, I'll probably do a tutorial on that in the coming weeks
i had a bad habit of only using replit, so switching to linux is very confusing to me. Can you explain how you have your code in the left and command on the right?
How the hell do you get the terminal giu while running gdb? I have not seen that before
i have lldb compatible to Mac M2. the commands are not the same.
hey I'm not able to see the source code even tho I have put the -g tag... I only get the logs :(
i’m in cs50 and used a function called get_string, when i did the compiler code, gcc -o substitution substitution.c -g, it gave me an error saying undefined reference to ‘get_string’
You probably called the function before you defined it. At the top of the file put the function prototype so the compiler knows it exists.
Hi, may I know the details of the environment that you are using for the demonstration? Thanks for this video.
I had no clue you could view the source as you stepped through the program like that. I also didn't know about next, so I always stepped into functions whenever I was stepping the program. It was really annoying because I'm using C++ (sorry not sorry to the C++ haters) and there are obviously a lot of native C++ code which does a lot of weird shit that we don't want to examine as the cause of our error
6:00 that's not an intel instruction, that's an at&t instruction
Hello, necromancer here. I tried this example code but my gcc does not warn about pointer on debian wsl. Is it because of settings or what? If I type int *d = 2; it shows warning.
cool
( 2:25 ) argc=21845. Why is it this random value and not 1 ( as argv[0]='a.out' ) ?
Whose job is it to set that value, bash or the OS?
That's a great question, I'm actually not sure. 21845 is 0x5555 in hex, so it may be a bug in GDB with 64-bit programs? I'll keep digging.
@@LowLevelLearning I tried this in Win10 WSL (Ubuntu) and it comes up with 0x0, thus it is likely just some bug.
At that line the argc was uninitialized, that's just how it works
@@dandan-gf4jk why would it be uninitialized? It is a function parameter and we are passing in only one argument so argc should be 1. If it isn't, it sounds like a bug.
@@AmanSingh-sp6bi I just explained it to you, but if you don't trust me go ahead submit the bug to gdb and report back.
👍
🎉
tui e is so OP
My code is so catastrophic that GDB segfaults...
This is great. I just wish you were a little slower, it' s too much info in one punch
I would not include anything about assembly language in a tutorial that is supposed to cover the basics of GDB. You also go too fast when typing/entering commands, requiring the viewer to go back and pause the video to see what you did.
Nobody needs low level nowadays. I used to do lots of low level coding. Os writing, drivers,... lots of cross platform... asm c c++ ... now script kiddies in jscript cobble together stuff.
Yes they do but only big companies doing adult stuff like compilers, OS, libraries, browsers, DBMS, high performance software etc. Yes less people are using low level today because everybody is programming using a hight level abstraction over a low level implementation already done by some really smart guys like the author of this video, for example today everybody programms in javascript so they think that C++, assembly x64 is not useful but javascript is executed by in Chrome by the interpreter V8 Engine(parses and executes javascript) that was created in C++ by google developers then in the end javascript developers ended up running C++. Java developers code in java with is translated to bytecodes with is runned by the JVM(created using C++). Python interpreter are created with C++ and used in the backend of his interpreters the C++ libraries for performance. Linux, Windows, etc were created and and run C++, assembly code than if you boot you PC you execute with UEFI(firmware made with low level coding) as the first thing and then loads your OS. Then everybody is always using low level but is transparent to then. Yes most developers don't use low level because others developers usually much more smart and prepared already created stairs for the theirs children(the rest of the developers) to follow. Yes this make the life of the 99% of the developers much more easy. It is the same atitude as the people who are only live today because they taked vacines when were children but become adults and out of complete ignorance think that vacinnes are a bad thing when they woudn't even been alive today if were not because of the vaccines. I'm personally very greateful for both the really smart people who can create vaccines and low level so I can just make 'lego programming'(easy but 'build' software fast and earn money) and pay my debts in the end of the month.
hahaha, you are so wrong. I do low level every day.
I am working with C++ and for 6 years haven't seen a single reason to go low level. Write your code, fix a bug (it will be a logical one or nullptr) and have your fun with compiler can't link shit for whole day. And than half an hour of compilation, multiply it 2/10 times and your life is wasted for today.
@dadlord689 well you don't do the sort of job I do then. And if you think C++ isn't low level then think again. Haha
@@turdwarbler Well, I am just doing job. I would combine languages, do the job and forget it. Most languages and tools are just stone age type. Maybe ai will help crate something actually useful but overall it is just digging ground with a stick. Almost impossible to be anywhat productive as a single developer while you actually capable to architecture so much more per day. Heay, I don't mind anyone liking it.
Or you know, use an IDE like VS 22 🤡