4 ms·

Based on the generated code, you may need to broaden the definition of "binary" to include anything that is executable (shell script.)

chungy 6y ago
It's not really a shell script though, it just looks like one enough to the point that a bourne shell can modify it to be directly executable. I'd probably be most worried about the bourne shell part. It seems like it'll be easy for this to break on any "non-standard" shell that Linux might execute.
- icedchai 6y ago
  This is true, but the shell is executing it "as if" it were a script, right? Until the binary part takes over...
- jart 6y ago
  The behavior that Cosmopolitan needs is required by POSIX because UNIX Sixth Edition didn't have shebang lines. It's normally an implementation detail of execve() in C libraries and the behavior is implemented by nearly all shells too. So far the only issue has been that some shells, like zsh, have a binary safety check where it refuses to run scripts that have embedded NUL characters. I worked with the FreeBSD team to get POSIX revised to clarify the correct behavior w.r.t. these restrictions. FreeBSD's /bin/sh has already been patched and zsh is pending upstream. https://github.com/jart/zsh/commit/94a4bc14bb2e415ec3d10cf716512bd3e0d99f48 https://github.com/jart/zsh/commit/94a4bc14bb2e415ec3d10cf71...
  - ashkankiani 6y ago
    I appreciate the thoroughness with which you are pursuing this. The amount of work you're doing outside of the technical aspect is definitely something I can admit that I would've never pursued. It's encouraging to see.
fao_ 6y ago
/bin/sh execution is supported at the kernel level iirc? Like, the minimum requirement for a linux distribution is /bin/sh, the rest of the system doesn't have to be there necessarily.
- deleted 6y ago
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- deleted 6y ago
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- 10000truths 6y ago
  No, the Linux kernel only requires an init executable to run. It otherwise makes no assumptions about the programs available in userland. Pretty much any sane/usable Linux distribution will package a shell, though.
  - saagarjha 6y ago
    It does, however, hardcode /bin/sh as a init of last resort: https://github.com/torvalds/linux/blob/dcc0b49040c70ad827a7f3d58a21b01fdb14e749/init/main.c#L1476 https://github.com/torvalds/linux/blob/dcc0b49040c70ad827a7f...
    - fao_ 6y ago
      Exactly what I was talking about, thank you
- saagarjha 6y ago
  The behavior your are likely thinking of (execvp on a file without a shebang) is implemented in libc.
  - fao_ 6y ago
    No. As someone else mentioned, the kernel hardcodes /bin/sh as a last resort: https://github.com/torvalds/linux/blob/dcc0b49040c70ad827a7f3d58a21b01fdb14e749/init/main.c#L1476 https://github.com/torvalds/linux/blob/dcc0b49040c70ad827a7f...

chungy 6y ago

It's not really a shell script though, it just looks like one enough to the point that a bourne shell can modify it to be directly executable. I'd probably be most worried about the bourne shell part. It seems like it'll be easy for this to break on any "non-standard" shell that Linux might execute.

icedchai 6y ago
This is true, but the shell is executing it "as if" it were a script, right? Until the binary part takes over...
jart 6y ago
The behavior that Cosmopolitan needs is required by POSIX because UNIX Sixth Edition didn't have shebang lines. It's normally an implementation detail of execve() in C libraries and the behavior is implemented by nearly all shells too. So far the only issue has been that some shells, like zsh, have a binary safety check where it refuses to run scripts that have embedded NUL characters. I worked with the FreeBSD team to get POSIX revised to clarify the correct behavior w.r.t. these restrictions. FreeBSD's /bin/sh has already been patched and zsh is pending upstream. https://github.com/jart/zsh/commit/94a4bc14bb2e415ec3d10cf716512bd3e0d99f48 https://github.com/jart/zsh/commit/94a4bc14bb2e415ec3d10cf71...
- ashkankiani 6y ago
  I appreciate the thoroughness with which you are pursuing this. The amount of work you're doing outside of the technical aspect is definitely something I can admit that I would've never pursued. It's encouraging to see.

fao_ 6y ago

/bin/sh execution is supported at the kernel level iirc? Like, the minimum requirement for a linux distribution is /bin/sh, the rest of the system doesn't have to be there necessarily.

deleted 6y ago
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deleted 6y ago
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10000truths 6y ago
No, the Linux kernel only requires an init executable to run. It otherwise makes no assumptions about the programs available in userland. Pretty much any sane/usable Linux distribution will package a shell, though.
- saagarjha 6y ago
  It does, however, hardcode /bin/sh as a init of last resort: https://github.com/torvalds/linux/blob/dcc0b49040c70ad827a7f3d58a21b01fdb14e749/init/main.c#L1476 https://github.com/torvalds/linux/blob/dcc0b49040c70ad827a7f...
  - fao_ 6y ago
    Exactly what I was talking about, thank you
saagarjha 6y ago
The behavior your are likely thinking of (execvp on a file without a shebang) is implemented in libc.
- fao_ 6y ago
  No. As someone else mentioned, the kernel hardcodes /bin/sh as a last resort: https://github.com/torvalds/linux/blob/dcc0b49040c70ad827a7f3d58a21b01fdb14e749/init/main.c#L1476 https://github.com/torvalds/linux/blob/dcc0b49040c70ad827a7f...