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Message-ID: <20140827205139.GT12888@brightrain.aerifal.cx>
Date: Wed, 27 Aug 2014 16:51:40 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: static build and dlopen
On Wed, Aug 27, 2014 at 10:19:18PM +0200, piranna@...il.com wrote:
> >> Yes, I though about this option before, has a dumb statically linked
> >> executable to work as PID 1 that just only exec Node.js and wait until
> >> it finishes, so I can use a standard dynamically linked one and do
> >> whatever I want
> >
> > I don't understand why you can't do whatever you want anyway.
> > You can run Node.js as PID 1 even if it is dynamically linked - you
> > just need to have the libc (and ld-musl.so) in the filesystem. It
> > will work. You can run anything as PID 1 provided all its dependencies
> > are there at boot time. Traditional inits are usually dynamically
> > linked - which I think is a very bad idea, but that's another subject.
> > If Node.js is a special case that cannot be treated that way, then I'm
> > interested in hearing why.
>
> I tried to do it that way, but didn't worked. Seems on Linux when you
> are using a dynamically linked executable this is not run directly,
> but instead it is exec internally /lib/ld-linux.so.2, that's a program
> that load and link your executable and it's dynamic libraries and
> later exec it, so it takes the PID 1 and when it finish and give
> control to your dynamically linked executable (Node.js in this case),
> then since PID 1 has exited, the kernel has a kernel panic. The same
> happens if using /usr/bin/env as she-bang, since it will get the PID 1
> and fail. You can read all that I have learned about this topics on
> https://github.com/NodeOS/NodeOS-Docker/pull/12.
This analysis is incorrect. Dynamic-linked programs do not involve
multiple processes where the dynamic linker runs in the parent process
and exits once the child is loaded; this would break absolutely
everything. Whether you took the approach I described (a wrapper
program that exec's ld-musl with the right arguments) or just using
the dynamic-linked program directly (if you can ensure that the
dynamic linker is available at the right pathname, which I think you
can), it will run as PID 1 and everything will work as expected.
> By the way, based on this example
> (http://www.cs.utah.edu/dept/old/texinfo/glibc-manual-0.02/library_23.html#SEC410)
> I've done a dumb /init program that just exec the dynamically linked
> Node.js with the real /init in Javascript and it worked. Ugly hack,
> but at least it does its job :-)
I think you could just directly use the dynamically linked Node.js
here, without the wrapper; you haven't given any indication of why
this would not work.
Rich
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