The author's blog is a FANTASTIC source of information. I recommend checking out some of their other posts: - https://mcyoung.xyz/2021/06/01/linker-script/ - https://mcyoung.xyz/2023/08/09/yarns/ - https://mcyoung.xyz/2023/08/01/llvm-ir/
Given TFA's bias against GCC, I'm not so sure. e.g. looking at the linker script article… it's also missing the __start_XYZ and __stop_XYZ symbols automatically created by the linker.
Sections and segments are more or less the same concept: metadata that tells the loader how to map each part of the file into the correct memory regions with the correct memory protection attributes. Biggest difference is segments don't have names. Also they aren't neatly organized into logical blocks like sections are, they're just big file extents. The segments table is essentially a table of arguments for the mmap system call.
Learning this stuff from scratch was pretty tough. Linker script has commands to manipulate the program header table but I couldn't figure those out. In the end I asked developers to add command line options instead and the maintainer of mold actually obliged.
Looks like very few people know about stuff like this. One can use it to do some heavy wizardry though. I leveraged this machinery into a cool mechanism for embedding arbitrary data into ELF files. The kernel just memory maps the data in before the program has even begun execution. Typical solutions involve the program finding its own executable on the file system, reading it into memory and then finding some embedded data section. I made the kernel do almost all of that automatically.
https://www.matheusmoreira.com/articles/self-contained-lone-...