Show HN: A (marginally) useful x86-64 ELF executable in 301 bytes

[−] vparseval 36d ago

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.

[−] qcoudeyr 36d ago

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

[−] meribold 34d ago

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.

[−] captn3m0 36d ago

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

[−] bArray 36d 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).

[−] emanuele-em 39d ago

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?

[−] zahlman 36d ago

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.

[−] sjdv1982 36d ago

Haha this is great!

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

[−] billforsternz 36d ago

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.

[−] anonymous67453 36d ago

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

[−] meribold 36d ago

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.

[−] meribold 34d ago

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

[−] userbinator 36d ago

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.

[−] meribold 36d ago

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...

Show HN: A (marginally) useful x86-64 ELF executable in 301 bytes (github.com)

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