[Android Q&A, Help & Troubleshooting] oxiroxt:
Hello,

I'm willing to try and build a custom rom, but I've been diving through the site for a few days and I still don't get it. I believe I do have the required background to do this: programming, linux, etc. and I have wide experience as a phone user, etc. It's just that either I'm not reading what I need or the way I want it. The problem, I believe, is that all I find are guides telling me to install this and those tools and then open this and that and voila! you got your rom. But they're not explaining WHAT exactly goes into those roms, or what is expected to go there, what's the purpose of those contents, etc., and I can't really catch with that. I feel at a loss and hate wasting my time turning around for nothing.

1. I don't understand the difference between a flashable rom and one that is meant to be installed through recovery, although I can see they're different. Do they both models contain the same kind of data? Is there any restriction to what one model can contain over the other one? If so, how would I convert from one to the other? But please, don't tell me to use this or that tool. I just need the theory behind it. Something of sorts like: "You need to extract this or that from this tarball, then mount this image, then the directory tree there goes in that directory over the other model of rom"

2. update-binary: Okay I guess this is run when installing from recovery, and this takes care of installing the rom, right?wrong?. Is this a per-rom thing, per-device thing? generic? If it's per-rom, how to generate it? do I need to compile something? Is there any generic source code that can be used as a start?

3. Although I have a basic understanding of how the Linux directory tree works, I know Android works on top of a heavily modified Linux. So can you explain briefly how the directory tree works? For instance, I believe /data/data is where Android apps install to, in /system/bin or xbin I can find busybox binaries/symlinks if present. /dev and /proc look the same as in Linux. I don't know about /sys. Also how are both rom models deployed to this tree? What is basically being copied?

4. If I were to compile a kernel, where do I find the Android kernel sources? or is it just a generic Linux kernel? where can i get a basic config for the device? Last time I checked my device hadn't /proc/config.gz but maybe I could get it from another rom with it enabled or something. What toolchain and where to get it? Oh and if you know of a native arm version of gcc or whatsnot, I'd prefer that. Setting up IDEs or toolchains is a nightmare. I don't like crosscompiling. But crosscompiling or not, a directory with all needed binaries without needing to set up system variables nor other stuff, would be amazing.

I surely have a lot more questions that I can't get from the back of my mind now, and I'll have yet more as you explain. But the point of my questions was mainly trying to explain the degree of the loss I'm at, so you can assist me better.

If it looks like a foolish petition, well, that's because I'm quite stubborn and can't catch things that don't go my way. I really need to understand the basics before I can move into actually doing something. I want to build a rom for the right reasons(to me). It's not just about packing a set of apps or themes with it, but about learning and doing other stuff like trying to fix things that are not supposed to work for the device in that Android version, etc.

If you can't help, congrats for reading through here anyways :D But any help is greatly appreciated :good: