4 ms·

Binfmtc – binfmt_misc C scripting interface

103 points by todsacerdoti 1y ago

zx2c4 1y ago
Similar project of mine from a long while ago: https://git.zx2c4.com/cscript/about/ https://git.zx2c4.com/cscript/about/
Surac 1y ago
So lovely
elitepleb 1y ago
similar to http://www.iq0.com/duffgram/com.html http://www.iq0.com/duffgram/com.html
JSR_FDED 1y ago
C is still my first love. You can hold the whole language in your head, and it’s fast. Yes there are footguns but it’s a libertarian programming language - you’re responsible for what you build. No hand holding.
- throwaway984393 1y ago
  [dead]
- ykonstant 1y ago
  I like that too, but the problem is that C doesn't keep its end of the deal. No hand holding, but make what you are doing transparent. It used to be the case back in the 80s, but not anymore. Not with our optimizing compilers and oodles of UB and spec subtleties and implicit actions.
radiospiel 1y ago
Amazing; when I tried something similar I used a "#!" line pointing to a C compiler + runner of sorts (https://github.com/radiospiel/jit https://github.com/radiospiel/jit). https://git.zx2c4.com/cscript/about/ https://git.zx2c4.com/cscript/about/ is also following that approach. What is the benefit of registering an extension via binfmt_misc?
- lmz 1y ago
  It's still valid C source code? Is the #! sequence valid C?
enriquto 1y ago
was surprised that "sudo apt install binfmtc" works out of the box on my box (linux mint) and i can do the magic just as described here
rwmj 1y ago
You can already do this without using binfmt ... #if 0 gcc "$0" -o "$@".out && exec ./"$@".out #endif #include <stdio.h> int main () { printf ("hello, world\n"); return 0; } Usage: $ chmod +x print.c $ ./print.c hello, world (Could be better to use a temporary file though.) There's a similar cute trick for compiled OCaml scripts that we use with nbdkit: https://libguestfs.org/nbdkit-cc-plugin.3.html#Using-this-plugin-with-OCaml https://libguestfs.org/nbdkit-cc-plugin.3.html#Using-this-pl...
- mananaysiempre 1y ago
  Compiler errors won’t cause as many funny consequences with gcc "$0" -o "$@".out && exec ./"$@".out || exit $? # I'd use ${0%.c} not $@ Love this trick too, but the difference, as far as I understand, is that it only works with a Bourne(-compatible) shell, whereas shebangs or binfmt_misc also work with exec().
- AlotOfReading 1y ago
  You can also #embed the compiler binary, and execve it to much the same effect as binfmtc. I explored that trick for an IOCC entry that was never submitted because it ended up far too readable.
- ckastner 1y ago
  Oh this is neat. Took me a bit. The shell treats the first line as a comment. It executes the second line, which eventually exec's the binary so the rest of the file do not matter to the shell. And the compiler treats the first line as a preprocessor directive, so it ignores the second line. I initially misread/mistook the first line for a shebang.
- teo_zero 1y ago
  The use of $@ doesn't look right to me. In the trivial case exposed here where there are no additional arguments to pass to the .c program, the shell executes gcc "print.c" -o .out && exec ./.out and it works "by chance". In a more complex scenario where print.c expects some parameters, it won't work. For example, ./print.c a b c will result in the shell trying to invoke gcc "print.c" -o "a" "b" "c".out && exec ./"a" "b" "c".out which makes no sense. Are you sure you didn't intend $0 instead of $@ ?
monocasa 1y ago
There's also tcc, which has a shebang compatible extension to allow it to be used by scripts.
kazinator 1y ago
This is doable entirely without a Linux-specific binfmt-misc hack. https://rosettacode.org/wiki/Multiline_shebang#C https://rosettacode.org/wiki/Multiline_shebang#C
- enriquto 1y ago
  This is a neat hack, but the whole file is not a valid C program.
  - kazinator 1y ago
    You mean it consists of a C program, plus non-C cruft to get it running? Isn't that already legitimized by configure scripts, compiler command lines and Make files?
    - enriquto 1y ago
      of course it is legitimized. I just meant that the selling point of binfmtc is that the same .c file can either be compiled by any C compiler, or executed directly.
      - kazinator 1y ago
        We could perhaps split it into a two-file system where a "foo.sh" containing certain boilerplate will execute a "foo.c" that doesn't require any special conventions at all. "foo.sh" could be identical for any .c file, and so we could symbolically link them all to a common file. Of course, neither that file nor symlinks to it require a .sh suffix. The contents might look like this: #!/bin/sh c_file=${0%.sh}.c x_file=${0%.sh}.bin # If cached executable file is missing, or out of date w.r.t. # the source file, compile it: if [ "$c_file" -nt "$x_file" ]; then cc $CFLAGS "$c_file" -o "$x_file" fi # Run cached executable file $x_file
codr7 1y ago
I did a simple hack for doing the same thing from inside a C program for my book: https://github.com/codr7/hacktical-c/tree/main/dynamic https://github.com/codr7/hacktical-c/tree/main/dynamic
rurban 1y ago
(2006)

103 points by todsacerdoti 1y ago

Similar project of mine from a long while ago: https://git.zx2c4.com/cscript/about/ https://git.zx2c4.com/cscript/about/

Surac 1y ago

So lovely

elitepleb 1y ago

similar to http://www.iq0.com/duffgram/com.html http://www.iq0.com/duffgram/com.html

JSR_FDED 1y ago

C is still my first love. You can hold the whole language in your head, and it’s fast. Yes there are footguns but it’s a libertarian programming language - you’re responsible for what you build. No hand holding.

throwaway984393 1y ago
[dead]
ykonstant 1y ago
I like that too, but the problem is that C doesn't keep its end of the deal. No hand holding, but make what you are doing transparent. It used to be the case back in the 80s, but not anymore. Not with our optimizing compilers and oodles of UB and spec subtleties and implicit actions.

radiospiel 1y ago

Amazing; when I tried something similar I used a "#!" line pointing to a C compiler + runner of sorts (https://github.com/radiospiel/jit https://github.com/radiospiel/jit). https://git.zx2c4.com/cscript/about/ https://git.zx2c4.com/cscript/about/ is also following that approach. What is the benefit of registering an extension via binfmt_misc?

lmz 1y ago
It's still valid C source code? Is the #! sequence valid C?

enriquto 1y ago

was surprised that "sudo apt install binfmtc" works out of the box on my box (linux mint) and i can do the magic just as described here

rwmj 1y ago

You can already do this without using binfmt ... #if 0 gcc "$0" -o "$@".out && exec ./"$@".out #endif #include <stdio.h> int main () { printf ("hello, world\n"); return 0; } Usage: $ chmod +x print.c $ ./print.c hello, world (Could be better to use a temporary file though.) There's a similar cute trick for compiled OCaml scripts that we use with nbdkit: https://libguestfs.org/nbdkit-cc-plugin.3.html#Using-this-plugin-with-OCaml https://libguestfs.org/nbdkit-cc-plugin.3.html#Using-this-pl...

mananaysiempre 1y ago
Compiler errors won’t cause as many funny consequences with gcc "$0" -o "$@".out && exec ./"$@".out || exit $? # I'd use ${0%.c} not $@ Love this trick too, but the difference, as far as I understand, is that it only works with a Bourne(-compatible) shell, whereas shebangs or binfmt_misc also work with exec().
AlotOfReading 1y ago
You can also #embed the compiler binary, and execve it to much the same effect as binfmtc. I explored that trick for an IOCC entry that was never submitted because it ended up far too readable.
ckastner 1y ago
Oh this is neat. Took me a bit. The shell treats the first line as a comment. It executes the second line, which eventually exec's the binary so the rest of the file do not matter to the shell. And the compiler treats the first line as a preprocessor directive, so it ignores the second line. I initially misread/mistook the first line for a shebang.
teo_zero 1y ago
The use of $@ doesn't look right to me. In the trivial case exposed here where there are no additional arguments to pass to the .c program, the shell executes gcc "print.c" -o .out && exec ./.out and it works "by chance". In a more complex scenario where print.c expects some parameters, it won't work. For example, ./print.c a b c will result in the shell trying to invoke gcc "print.c" -o "a" "b" "c".out && exec ./"a" "b" "c".out which makes no sense. Are you sure you didn't intend $0 instead of $@ ?

monocasa 1y ago

There's also tcc, which has a shebang compatible extension to allow it to be used by scripts.

kazinator 1y ago

This is doable entirely without a Linux-specific binfmt-misc hack. https://rosettacode.org/wiki/Multiline_shebang#C https://rosettacode.org/wiki/Multiline_shebang#C

enriquto 1y ago
This is a neat hack, but the whole file is not a valid C program.
- kazinator 1y ago
  You mean it consists of a C program, plus non-C cruft to get it running? Isn't that already legitimized by configure scripts, compiler command lines and Make files?
  - enriquto 1y ago
    of course it is legitimized. I just meant that the selling point of binfmtc is that the same .c file can either be compiled by any C compiler, or executed directly.
    - kazinator 1y ago
      We could perhaps split it into a two-file system where a "foo.sh" containing certain boilerplate will execute a "foo.c" that doesn't require any special conventions at all. "foo.sh" could be identical for any .c file, and so we could symbolically link them all to a common file. Of course, neither that file nor symlinks to it require a .sh suffix. The contents might look like this: #!/bin/sh c_file=${0%.sh}.c x_file=${0%.sh}.bin # If cached executable file is missing, or out of date w.r.t. # the source file, compile it: if [ "$c_file" -nt "$x_file" ]; then cc $CFLAGS "$c_file" -o "$x_file" fi # Run cached executable file $x_file

codr7 1y ago

I did a simple hack for doing the same thing from inside a C program for my book: https://github.com/codr7/hacktical-c/tree/main/dynamic https://github.com/codr7/hacktical-c/tree/main/dynamic

rurban 1y ago

(2006)