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Creating Really Teensy ELF Executables for Linux

47 points by dexen 12y ago

jcr 12y ago
This article is surprisingly better (and longer ;) than I expected, but it skipped over explaining one important distinction; "ELF" is an executable file format, but "a.out" is more than just a default file name; it's also the name of a totally different executable file format. Originally, the "a.out" executable format, and hence, the "a.out" file name were due to being the "assembler output" of Ken Thompson's assembler in 1968. Most all UNIX-based systems have moved to using newer ELF format, but there are a few hold-outs still using the older a.out format. As for why ELF formatted executable files are still given the file name "a.out" by default, even when they are not in the "a.out" executable format, it's just a historic artifact (or annoyance) due to compilers and linkers. http://en.wikipedia.org/wiki/A.out http://en.wikipedia.org/wiki/A.out
- pkrumins 12y ago
  This is the original article that all the other "tiny elf" or "tiny executable" articles are based on. It was written 15 years ago.
listic 12y ago
Care to update for 64 bits?
- caust1c 12y ago
  Here are the uncommented changes I made to each stage: https://github.com/abraithwaite/teensy https://github.com/abraithwaite/teensy
qwerta 12y ago
Nice. Perhaps have a look at uclibc and busybox... :-)
- gfto 12y ago
  These are not really small anymore. Look for musl libc [1] and toybox [2] instead. [1]: http://www.musl-libc.org/ http://www.musl-libc.org/ [2]: http://www.landley.net/toybox/ http://www.landley.net/toybox/
cache87 12y ago
That's what I loved about DOS com executables. Possibly the smallest program was: int 20; which got translated into CDh 20h (4 bytes!)
- rcarmo 12y ago
  I had a friend in college who once coded an entire lotto program ("graphics" and all) into 380-odd bytes. Utterly insane.
- xyproto 12y ago
  That's 2 bytes, not 4. A byte goes from 00 to FF.
- fit2rule 12y ago
  Smallest useful DOS program I ever wrote was FF FF, or in other words .. reboot! :)
mistaken 12y ago
I was hoping that the final size would be 42 :)
whitten 12y ago
I'm impressed. The author did a lot of mangling to allow the code to be as small as possible. Other than ELF and a.out format, (which is discused by @jcr) I wonder if there are other formats understood by Linux ?
sctb 12y ago
https://news.ycombinator.com/item?id=8642734 https://news.ycombinator.com/item?id=8642734

47 points by dexen 12y ago

jcr 12y ago

This article is surprisingly better (and longer ;) than I expected, but it skipped over explaining one important distinction; "ELF" is an executable file format, but "a.out" is more than just a default file name; it's also the name of a totally different executable file format. Originally, the "a.out" executable format, and hence, the "a.out" file name were due to being the "assembler output" of Ken Thompson's assembler in 1968. Most all UNIX-based systems have moved to using newer ELF format, but there are a few hold-outs still using the older a.out format. As for why ELF formatted executable files are still given the file name "a.out" by default, even when they are not in the "a.out" executable format, it's just a historic artifact (or annoyance) due to compilers and linkers. http://en.wikipedia.org/wiki/A.out http://en.wikipedia.org/wiki/A.out

pkrumins 12y ago
This is the original article that all the other "tiny elf" or "tiny executable" articles are based on. It was written 15 years ago.

listic 12y ago

Care to update for 64 bits?

caust1c 12y ago
Here are the uncommented changes I made to each stage: https://github.com/abraithwaite/teensy https://github.com/abraithwaite/teensy

qwerta 12y ago

Nice. Perhaps have a look at uclibc and busybox... :-)

gfto 12y ago
These are not really small anymore. Look for musl libc [1] and toybox [2] instead. [1]: http://www.musl-libc.org/ http://www.musl-libc.org/ [2]: http://www.landley.net/toybox/ http://www.landley.net/toybox/

cache87 12y ago

That's what I loved about DOS com executables. Possibly the smallest program was: int 20; which got translated into CDh 20h (4 bytes!)

rcarmo 12y ago
I had a friend in college who once coded an entire lotto program ("graphics" and all) into 380-odd bytes. Utterly insane.
xyproto 12y ago
That's 2 bytes, not 4. A byte goes from 00 to FF.
fit2rule 12y ago
Smallest useful DOS program I ever wrote was FF FF, or in other words .. reboot! :)

mistaken 12y ago

I was hoping that the final size would be 42 :)

whitten 12y ago

I'm impressed. The author did a lot of mangling to allow the code to be as small as possible. Other than ELF and a.out format, (which is discused by @jcr) I wonder if there are other formats understood by Linux ?

sctb 12y ago

https://news.ycombinator.com/item?id=8642734 https://news.ycombinator.com/item?id=8642734