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It's to help keep you awake.

The -l option (lowercase L) tells gcc that we want to link to a specific library. The convention is to use the name of the library, without the 'lib' prefix. So, if we have a library called libmath, then we drop the 'lib' part of it to get just 'math'. Then we append that to the -l to get: -lmath In this video, libmath is the static library that I created in the first half of the video using the 'ar' command.

You can compile it for yourself

Thanks for your support. Yes, I do plan to do some videos like that in the future.

Thanks for your comments. This is a good question; probably worthy of an entire video in response. Linux makes use of something called virtual memory management. From the processes point of view, it has access to the full process address space allocated to it. Another process would think it has access to the exact same address range. But these addresses do not translate directly to the physical RAM address space. The process memory is logically split into pages of a certain size and the physical RAM is also split into page frames of the same size. The Linux OS will map a process's page to a page frame in physical RAM. So, when the process is accessing a page in its own process memory space, the OS will look up the physical RAM page frame that it maps to and read the data from there. This process page to RAM page frame mapping is called a page table. Generally processes have to share the physical RAM. So, when a process needs data that is not currently in RAM, and assuming RAM is full, the OS will need to make space, so it will write data from a RAM page frame into a temporary non-volatile storage. Then it will repurpose that physical page frame for the new process. Most Linux systems will have a partition called the swap partition. This is where data from RAM is written to and read from in order help facilitate RAM sharing. There is a lot to this topic, but I hope this explanation helps you understand it. Please ask again if it is not clear. Here's a link with some info: tldp.org/LDP/sag/html/vm-intro.html#:~:text=Linux%20supports%20virtual%20memory%2C%20that,be%20used%20for%20another%20purpose. This link has a diagram which I think is useful (see Section 3.) tldp.org/LDP/tlk/mm/memory.html

Thanks. I'm glad you found it useful.

I second this.

It's been too long. I'm glad to be back to making videos.

@@embeddedarmdev bro I’ve watched your videos multiple times and I was saddened to see that you didn’t post anymore, but Welcome back!!

You are correct. The last byte is 0x33, not 0x34. Unfortunately, TH-cam does not support annotations anymore so I pointed out the error in the description.

@@embeddedarmdev Ah I didn’t notice - I have a bad habit of forgetting to check descriptions. Cheers

No, you're good. I updated the description after you pointed out the error. Thanks for bringing it to my attention.

The tuple I am discussing here is for the target machine, not your host. So, you want to choose the architecture that the binary is expected to run on. In this video, we are compiling for an ARM processor, so I chose an ARM tuple.

@@embeddedarmdev Ok, I see, like compiling for a raspberry pi. Is that I was expecting to see you using the library with some examples and not just compiling it. Thanks for the videos.

Yes, that is correct. So for the Raspberry Pi, you might choose linux-armv4 for a 32-bit Pi and linux-aarch64 for a 64-bit Pi (assuming they are running Linux). One thing I should also add is that the tuples you see in this video are what the Config utility is set up to use for this particular library (SSL). We see linux-armv4, so that would support armv4 instructions and would run on any processor that supports armv4 - armv7 since they are backwards compatible. Other libraries you find might use armv5 or higher. It just depends on the library. This video was focused specifically on cross-compiling a library, not really how to use a specific library in your code. The idea was to walk you through how to set up the configuration and specify all of the compiler options, include directories, library directories, etc. in order to cross-compile a library for some other architecture.

I appreciate your support. I'm a big advocate of free education and I don't want to limit access to only those that have money, so I chose this platform. I have considered starting up a Patreon, but I don't do enough content to warrant that. Perhaps in the future I will set one up. I do make some money off the ads. If you want to help, the best thing you can do is spread the word about my channel and encourage people to check it out.

Thank you. I'm glad you find the videos useful.

I'm not sure I understand your question. I don't know what you mean by "fold the constant". The -g option puts debugging information into the ELF, but does not change how the binary is linked. If your program uses an external library, you'll still have to link using the -l option. Does that answer your question?

Thanks for your comment. I do have this video here on sections th-cam.com/video/L9okXJH5l2Y/w-d-xo.html Is there something specific about sections you are looking for? I can add it to my list of future content.

Thanks. I'm glad you like it. Hope you found it useful.

Yes, I believe it is possible. There is something called FatELF that does that, but I have not explored it mush. I'm not sure what your use case for this is, but it may not be as portable as you are hoping. I am pretty sure it requires you to make a modification to your target system to support it and I am not sure which distros (if any) would support it out of the box. So, I don't think it is like you can just distribute this binary and it would work an anybody's system. One thing to consider is that your binary would be roughly twice the size as for just one architecture which could be a problem for embedded systems. I think it just makes more sense to compile a separate binary for each target, but I guess it depends on your use case.

@@embeddedarmdev thank you for the response, I have already found out about FatELF, somehow I was under impression that ELF format is similar to Apple's universal binaries. I am doing some research for my thesis work and I am looking into malware samples that can be universally executed on both aarch64 and x86_64 as we have such issue on MacOS for Apple Silicon. Anyway, thank you for your videos, they are quite useful <3

I see. That's an interesting thesis. I was looking at it from a development perspective. It's definitely possible to do that but I think either the loader would have to support it, or you'd have to trick the loader somehow.

Thank you. I'm glad you find them useful. I'm hoping to get back to making new videos very soon.

It would depend on what error it gave you. But I do know if you want to compile static, you need the static library (.a). You can't compile a static binary with a shared library (.so)

Yes, sorry, I let the domain expire. But I have renewed it. However, all it ever did was redirect to my TH-cam page. I hope to add actual content sometime in the future.

Yes, if you compile with the static flag, it will look for the .a file. Otherwise it looks for the .so If you try compiling for static and don't have the .a library, I believe it throws an error.

Thanks. Glad you found it useful!