Love it! It's entirely inapplicable and useless to me but it embodies the spirit of Show HN and what the spirit of programming in the 80s and 90s was.

This commit (https://github.com/meribold/btry/commit/75cba2be52cc8fbdc72b...) worked for me !

The new latest version (commit 806789e4d454b, 307 bytes) should also work. It no longer sets p_memsz to something unreasonably large, which was most likely the issue with the 301-byte and 298-byte versions from a few days ago.

I had a similar problem for a Thinkpad, except there is more than one cell at different capacities that are switched between. The existing battery manager would not tell me which battery was actually being used, and whether there was still a secondary battery waiting to be discharged.

I wrote a very quick hacky program for X11 that stays always visible that will display the information for any number of batteries: https://gitlab.com/danbarry16/bat_mon

It ends up being 50kB with minimal optimization and sports a lightweight X11 library (GUI) and JSON parser (configuration).

I have a use for this: A somewhat portable one-liner to go in my waybar/sway/i3 configs!

Dell 5440

    $ git clone https://github.com/meribold/btry
    ...
    $ make
    as -mx86-used-note=no btry.s -o btry.o
    objcopy -O binary btry.o btry
    chmod +x btry

    $ ./btry 
    Segmentation fault         ./btry

    $ strace -f ./btry 
    execve("./btry", ["./btry"], 0x7ffc1a562078 /* 57 vars */) = -1 ENOMEM (Cannot allocate memory)

    $ file btry
    btry: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, corrupted section header size

Looks like I may have stretched what values are acceptable for p_filesz/p_memsz too far. What's your kernel version? (I tested it on 6.8.0 and 4.4.0.) Perhaps the 316-byte version at commit 451827cfd5399074 (before that particular hack was introduced) would work.

I fixed the most likely culprit now (excessively large p_memsz value). It cost a few bytes; the new executable size is 307 bytes.

301 bytes! The base64 one-liner install is a nice flex. Accepting an infinite loop when energy_full doesn't exist is peak code golf, perfectly reasonable when every byte counts. Is there a writeup on the assembly somewhere?

The xz step doesn't seem to be doing very much, though. It seems the decoded data is currently 278 bytes versus a 298-byte decompressed result.

Haha this is great!

What about adding a Make rule to auto-generate the one-liner install from the binary?

I would prefer avoiding the infinite loop and printing a message to help the user understand what went wrong. I'm sure you could do that with an extra 100 bytes or so. Just my opinion of course.

It doesn't even look like particularly optimised Asm (could immediately spot a few savings, despite how horrible GAS syntax is to read...), but is definitely not "compiler slop"[1] either, which shows just how inefficient the majority of programs actually are. Of course even the ELF header takes up a significant amount of space, but this reminds me of how PC magazines would print short listings of utilities like this, often a few dozen up to a few hundred bytes at most --- in DOS .COM format, which is headerless and thus pure machine instructions.

[1] In the late 80s and early 90s, the battle between those writing handwritten Asm and those using compiled HLLs has many similarities to AI-generated vs non-AI code today.

If the savings are about `mov $1, %edi` and `mov $10, %ecx`, those 32-bit immediate values line up with the higher bytes of p_filesz and p_memsz in the program header, which have to be zero [1]. If not, what are the savings? :)

[1]: https://github.com/meribold/btry/commit/8ef5a4ce58ae73c489d2...

Love this kind of tiny, over‑engineered hack—totally impractical, but pure Show HN energy.

Really cool ! I like to see these kind of post here

As always with these admirable hacks, I feel compelled to point out these are not really ELF executables but just small files you can trick the x86_64 Linux kernel into loading.

I mean they're very clever and legit and kudos to the people who develop these exploits, but they're not ELF.

I'd agree it's not standards compliant. But if it's accepted as an ELF by Linux, in what way is it not an ELF?

Or to flip it round. If Linux accepts something as an ELF that isn't, then it isn't an ELF loader.

Would you describe a web browser that doesn't score 100% on a rendering test as not a browser?

The analogy would be more like a browser that somehow manages to render utterly broken HTML (yes, they actually do)

Is it really not ELF? The file starts with the \x7FELF magic, but I'm not by my laptop to see what `file btry` outputs.

GP is likely referring to how fields in the ELF and program header are abused for instructions and data in a way that happens to not break things on Linux.