4 ms·

A whirlwind tutorial on creating teensy ELF executables for Linux (1999)

59 points by xtacy 2y ago

dang 2y ago
Related. Others? A Whirlwind Tutorial on Creating Teensy ELF Executables for Linux - https://news.ycombinator.com/item?id=32524007 https://news.ycombinator.com/item?id=32524007 - Aug 2022 (10 comments) A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux (1999) - https://news.ycombinator.com/item?id=21846785 https://news.ycombinator.com/item?id=21846785 - Dec 2019 (22 comments) A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux (2005) - https://news.ycombinator.com/item?id=11709247 https://news.ycombinator.com/item?id=11709247 - May 2016 (5 comments) Creating Really Teensy ELF Executables for Linux - https://news.ycombinator.com/item?id=8745024 https://news.ycombinator.com/item?id=8745024 - Dec 2014 (13 comments) The Teensy Files: Creating teensy ELF executables for Linux - https://news.ycombinator.com/item?id=8642734 https://news.ycombinator.com/item?id=8642734 - Nov 2014 (7 comments) A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux - https://news.ycombinator.com/item?id=5016434 https://news.ycombinator.com/item?id=5016434 - Jan 2013 (14 comments) Tutorial on Creating Really Teensy ELF Executables for Linux - https://news.ycombinator.com/item?id=875077 https://news.ycombinator.com/item?id=875077 - Oct 2009 (16 comments) 3998-byte executable reduced to 45 bytes - https://news.ycombinator.com/item?id=68056 https://news.ycombinator.com/item?id=68056 - Oct 2007 (10 comments)
- jart 2y ago
  Plus if you want them to run on four OSes: https://justine.lol/sizetricks/#elf https://justine.lol/sizetricks/#elf
ptspts 2y ago
Shameless plug: write your program in C, get almost as little size overhead as in the Whirlwind turorial: https://github.com/pts/minilibc686 https://github.com/pts/minilibc686 (libc, compiler, linker, settings)
le-mark 2y ago
Does anyone recall an “intro to computing” style book that was available free online and starts with using the gas assembler and talked a lot about elf format executables? I lost the link a while ago and don’t recall the name.
- tiu 2y ago
  You are probably thinking about Programming from the Ground Up by Jonathan Bartlett. There are many others in the same style though. He also has a newer book if I recall right. https://www.amazon.com/Programming-Ground-Up-Jonathan-Bartlett/dp/1616100648 https://www.amazon.com/Programming-Ground-Up-Jonathan-Bartle... https://download-mirror.savannah.gnu.org/releases/pgubook/ https://download-mirror.savannah.gnu.org/releases/pgubook/
deater 2y ago
for those excited about tiny ELF executables, or tiny programs in general, check out the Lovebyte size-coding demoparty happening next weekend. It's likely there will be a few tiny ELF entries there.
- LegionMammal978 2y ago
  That's neat, I didn't know that there was much sizecoding activity with ELFs, except for the BGGP competitions [0]. (Mainly because it's not nearly as easy to output graphics than on all the old-school platforms, I'd imagine.) Does Lovebyte publish previous years' demos anywhere? [0] https://binary.golf/ https://binary.golf/
  - deater 2y ago
    I don't know if there's a good way to search for them. Most of the Lovebyte entries can be found on pouet or demozoo.org but I don't know if there's an easy way to filter out only Linux entries. I've written a few sizecoded raspberry pi entries, there's even a writeup of one of them in tmp.out where I loaded some code into the ELF headers https://tmpout.sh/3/08.html https://tmpout.sh/3/08.html
    - LegionMammal978 2y ago
      Ah, then I suppose you'd be aware of my own forays into 64-bit ELFs (https://tmpout.sh/3/22.html https://tmpout.sh/3/22.html)! I really should get around to publishing my writeup of the 73-byte minimum on Linux. (At least, it's 73 bytes for x86-64, since '\177E' at the start of the file jumps to byte 71, but it may be different under AArch64.) I have a nearly-complete draft, but I got caught on some oddities around the vDSO mapping which may or may not have changed across kernel versions, especially since the time I wrote it. Perhaps I should just jettison that section entirely and get the article out, since it's not like any of the x86 vDSOs have useful gadgets anyway.
    - duskwuff 2y ago
      Pouet certainly has platform filtering; try: https://www.pouet.net/prodlist.php?type[]=32b&type[]=64b&type[]=128b&type[]=256b&platform[]=Linux&order=release&reverse=1 https://www.pouet.net/prodlist.php?type[]=32b&type[]=64b&typ...
cryne 2y ago
I tried to replicate this on my 64 bit machine, so nasm -f elf64 tiny.s && ld -s tiny.o ; tiny.asm BITS 64 GLOBAL _start SECTION .text _start: mov eax, 1 mov ebx, 42 int 0x80 and this lands me at 4320 bytes! Why is there such a stark difference?
- oguz-ismail 2y ago
  > Why is there such a stark difference? Your linker must align the .text section to the page size (often 4096 bytes). If you open the binary with a hex editor you'll see lots of null padding.
  - yjftsjthsd-h 2y ago
    If that's a hard lower limit, then it really invites a different sort of code golf / demo to see how much functionality you can stuff into a 4K(ish) binary
    - oguz-ismail 2y ago
      > If that's a hard lower limit I think it's some sort of optimization (retrieving one page of memory should be easier than two, right?). With GNU ld I can do ld -s -Ttext=0x4000b0 tiny.o and shave off 3920 bytes on my system.
    - LegionMammal978 2y ago
      The real hard limit is 73 bytes [0], to actually run any code in the executable without segfaulting right away. You can cram about 3 simple syscalls into that limit (e.g., my BGGP4 submission [1], which copies the executable to another file), including the final exit() or exit_group() if you want your program to terminate cleanly. Strings are very costly: I couldn't get a Hello World below 77 bytes. [0] https://tmpout.sh/3/22.html https://tmpout.sh/3/22.html [1] https://github.com/binarygolf/BGGP/pull/3/files https://github.com/binarygolf/BGGP/pull/3/files, assembly at https://gist.github.com/LegionMammal978/347c939def56dcba449cb54dd9ee22f4 https://gist.github.com/LegionMammal978/347c939def56dcba449c...

59 points by xtacy 2y ago

dang 2y ago

Related. Others? A Whirlwind Tutorial on Creating Teensy ELF Executables for Linux - https://news.ycombinator.com/item?id=32524007 https://news.ycombinator.com/item?id=32524007 - Aug 2022 (10 comments) A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux (1999) - https://news.ycombinator.com/item?id=21846785 https://news.ycombinator.com/item?id=21846785 - Dec 2019 (22 comments) A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux (2005) - https://news.ycombinator.com/item?id=11709247 https://news.ycombinator.com/item?id=11709247 - May 2016 (5 comments) Creating Really Teensy ELF Executables for Linux - https://news.ycombinator.com/item?id=8745024 https://news.ycombinator.com/item?id=8745024 - Dec 2014 (13 comments) The Teensy Files: Creating teensy ELF executables for Linux - https://news.ycombinator.com/item?id=8642734 https://news.ycombinator.com/item?id=8642734 - Nov 2014 (7 comments) A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux - https://news.ycombinator.com/item?id=5016434 https://news.ycombinator.com/item?id=5016434 - Jan 2013 (14 comments) Tutorial on Creating Really Teensy ELF Executables for Linux - https://news.ycombinator.com/item?id=875077 https://news.ycombinator.com/item?id=875077 - Oct 2009 (16 comments) 3998-byte executable reduced to 45 bytes - https://news.ycombinator.com/item?id=68056 https://news.ycombinator.com/item?id=68056 - Oct 2007 (10 comments)

jart 2y ago
Plus if you want them to run on four OSes: https://justine.lol/sizetricks/#elf https://justine.lol/sizetricks/#elf

ptspts 2y ago

Shameless plug: write your program in C, get almost as little size overhead as in the Whirlwind turorial: https://github.com/pts/minilibc686 https://github.com/pts/minilibc686 (libc, compiler, linker, settings)

le-mark 2y ago

Does anyone recall an “intro to computing” style book that was available free online and starts with using the gas assembler and talked a lot about elf format executables? I lost the link a while ago and don’t recall the name.

tiu 2y ago
You are probably thinking about Programming from the Ground Up by Jonathan Bartlett. There are many others in the same style though. He also has a newer book if I recall right. https://www.amazon.com/Programming-Ground-Up-Jonathan-Bartlett/dp/1616100648 https://www.amazon.com/Programming-Ground-Up-Jonathan-Bartle... https://download-mirror.savannah.gnu.org/releases/pgubook/ https://download-mirror.savannah.gnu.org/releases/pgubook/

deater 2y ago

for those excited about tiny ELF executables, or tiny programs in general, check out the Lovebyte size-coding demoparty happening next weekend. It's likely there will be a few tiny ELF entries there.

LegionMammal978 2y ago
That's neat, I didn't know that there was much sizecoding activity with ELFs, except for the BGGP competitions [0]. (Mainly because it's not nearly as easy to output graphics than on all the old-school platforms, I'd imagine.) Does Lovebyte publish previous years' demos anywhere? [0] https://binary.golf/ https://binary.golf/
- deater 2y ago
  I don't know if there's a good way to search for them. Most of the Lovebyte entries can be found on pouet or demozoo.org but I don't know if there's an easy way to filter out only Linux entries. I've written a few sizecoded raspberry pi entries, there's even a writeup of one of them in tmp.out where I loaded some code into the ELF headers https://tmpout.sh/3/08.html https://tmpout.sh/3/08.html
  - LegionMammal978 2y ago
    Ah, then I suppose you'd be aware of my own forays into 64-bit ELFs (https://tmpout.sh/3/22.html https://tmpout.sh/3/22.html)! I really should get around to publishing my writeup of the 73-byte minimum on Linux. (At least, it's 73 bytes for x86-64, since '\177E' at the start of the file jumps to byte 71, but it may be different under AArch64.) I have a nearly-complete draft, but I got caught on some oddities around the vDSO mapping which may or may not have changed across kernel versions, especially since the time I wrote it. Perhaps I should just jettison that section entirely and get the article out, since it's not like any of the x86 vDSOs have useful gadgets anyway.
  - duskwuff 2y ago
    Pouet certainly has platform filtering; try: https://www.pouet.net/prodlist.php?type[]=32b&type[]=64b&type[]=128b&type[]=256b&platform[]=Linux&order=release&reverse=1 https://www.pouet.net/prodlist.php?type[]=32b&type[]=64b&typ...

cryne 2y ago

I tried to replicate this on my 64 bit machine, so nasm -f elf64 tiny.s && ld -s tiny.o ; tiny.asm BITS 64 GLOBAL _start SECTION .text _start: mov eax, 1 mov ebx, 42 int 0x80 and this lands me at 4320 bytes! Why is there such a stark difference?

oguz-ismail 2y ago
> Why is there such a stark difference? Your linker must align the .text section to the page size (often 4096 bytes). If you open the binary with a hex editor you'll see lots of null padding.
- yjftsjthsd-h 2y ago
  If that's a hard lower limit, then it really invites a different sort of code golf / demo to see how much functionality you can stuff into a 4K(ish) binary
  - oguz-ismail 2y ago
    > If that's a hard lower limit I think it's some sort of optimization (retrieving one page of memory should be easier than two, right?). With GNU ld I can do ld -s -Ttext=0x4000b0 tiny.o and shave off 3920 bytes on my system.
  - LegionMammal978 2y ago
    The real hard limit is 73 bytes [0], to actually run any code in the executable without segfaulting right away. You can cram about 3 simple syscalls into that limit (e.g., my BGGP4 submission [1], which copies the executable to another file), including the final exit() or exit_group() if you want your program to terminate cleanly. Strings are very costly: I couldn't get a Hello World below 77 bytes. [0] https://tmpout.sh/3/22.html https://tmpout.sh/3/22.html [1] https://github.com/binarygolf/BGGP/pull/3/files https://github.com/binarygolf/BGGP/pull/3/files, assembly at https://gist.github.com/LegionMammal978/347c939def56dcba449cb54dd9ee22f4 https://gist.github.com/LegionMammal978/347c939def56dcba449c...