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As I've said in other threads https://news.ycombinator.com/item?id=38847750#38862450 , I highly recommend writing an ELF by hand at least once. It's a great exercise to understand the basic parts of an executable. It's also helpful if you want to go the opposite direction of this article - bottom-up instead of top-down. Lots of other great discussion in various threads on that other HN post.
As I've said in other threads https://news.ycombinator.com/item?id=38847750#38862450 , I highly recommend writing an ELF by hand at least once. It's a great exercise to understand the basic parts of an executable. It's also helpful if you want to go the opposite direction of this article - bottom-up instead of top-down. Lots of other great discussion in various threads on that other HN post.
is ELF unique to x86/x64?
ELF is platform agnostic, and has been used in operating systems on nearly every existing CPU platform since mid 90's (with a few notable exceptions being OS X, AIX, the embedded world and Windows).
Earlier quoted context omitted.
Writing an ELF file by hand is something I did recently: https://github.com/avik-das/garlic/blob/master/recursive/elf... To explain the format to myself and others, I also created an interactive visualization for the bytes in the file. It helps me to click on a byte, see an explanation for it and see related bytes elsewhere in the file highlighted. https://scratchpad.avikdas.com/elf-explanation/elf-explanati...
That's an awesome interactive page! Did you write it by hand, or did you use some sort of generator/tool?
Also if you click two bytes that are in the same caption group one after another then it bugs out.
Not a criticism, not even a nit-pick, but a reflection "(binaries are kind of the definition of platform-specific, so this is all platform-specific) (this is true!) When "Actually Portable Executable" took the (geek) proved that the same binary could run on a bunch of platforms, that was a surreal moment I still haven't mentally recovered from. Here we spent decades trying to solve the cross-platform problem, in so m…
I may have misunderstood, but I'm pretty sure APE is not a "binary format" per se. It is a script that can be executed on any system. That script can then LOAD a binary. IIRC the original needed to decode it from base64 before it could be loaded. So... it's an executable binary loader
How can the syscalls work the same in linux, windows and n my macos?!
It’s bananas
Earlier quoted context omitted.
Writing an ELF file by hand is something I did recently: https://github.com/avik-das/garlic/blob/master/recursive/elf... To explain the format to myself and others, I also created an interactive visualization for the bytes in the file. It helps me to click on a byte, see an explanation for it and see related bytes elsewhere in the file highlighted. https://scratchpad.avikdas.com/elf-explanation/elf-explanati...
That's an awesome interactive page! Did you write it by hand, or did you use some sort of generator/tool?
Lately, I've been using Svelte for interactive visualizations (see my post on using a tool called Astro with Svelte: https://avikdas.com/2023/12/30/interactive-demos-using-astro... ). But this one is all hand-written JS!
As I've said in other threads https://news.ycombinator.com/item?id=38847750#38862450 , I highly recommend writing an ELF by hand at least once. It's a great exercise to understand the basic parts of an executable. It's also helpful if you want to go the opposite direction of this article - bottom-up instead of top-down. Lots of other great discussion in various threads on that other HN post.
Doing it is basically a hand assembly. One reads the documentation, selects the bytes needed using a processor data sheet, orders them into the various sections, populates the ELF fields and then it really does boil down to typing them all in.
Pre-ELF times, on say an 8 bit Apple 2, the machine code monitor, allowed input of the program bytes directly. Those are then executed.
Storing to disk is only a bit more involved, and there is another opportunity! Disk sector editors allow one to create a file...
...and so it goes!
As I've said in other threads https://news.ycombinator.com/item?id=38847750#38862450 , I highly recommend writing an ELF by hand at least once. It's a great exercise to understand the basic parts of an executable. It's also helpful if you want to go the opposite direction of this article - bottom-up instead of top-down. Lots of other great discussion in various threads on that other HN post.
Writing an ELF file by hand is something I did recently: https://github.com/avik-das/garlic/blob/master/recursive/elf... To explain the format to myself and others, I also created an interactive visualization for the bytes in the file. It helps me to click on a byte, see an explanation for it and see related bytes elsewhere in the file highlighted. https://scratchpad.avikdas.com/elf-explanation/elf-explanati...
Earlier quoted context omitted.
That's an awesome interactive page! Did you write it by hand, or did you use some sort of generator/tool?
I agree it’s very nice. I’d also like to know how it was done. Also if you click two bytes that are in the same caption group one after another then it bugs out.
For the bug, feel free to email me at avik at avikdas dot com if you'd like. The behavior I verified just now (for me) is that if you click one byte to highlight it, then clicking any other byte in the same group will remove the highlighting.
As I've said in other threads https://news.ycombinator.com/item?id=38847750#38862450 , I highly recommend writing an ELF by hand at least once. It's a great exercise to understand the basic parts of an executable. It's also helpful if you want to go the opposite direction of this article - bottom-up instead of top-down. Lots of other great discussion in various threads on that other HN post.
Writing an ELF file by hand is something I did recently: https://github.com/avik-das/garlic/blob/master/recursive/elf... To explain the format to myself and others, I also created an interactive visualization for the bytes in the file. It helps me to click on a byte, see an explanation for it and see related bytes elsewhere in the file highlighted. https://scratchpad.avikdas.com/elf-explanation/elf-explanati...