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Date: Wed, 2 Sep 2020 12:42:52 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: Ignoring dependencies libresolv and libcrypt
On Wed, Sep 02, 2020 at 07:14:10PM +0300, Nikos Dragazis wrote:
> Hi everyone,
>
> Apologies if this has already been answered before.
>
> I am experimenting with musl. I see that musl produces a single DSO with
> all symbols, as opposed to glibc which produces multiple DSOs
> (libthread, libm, librt, etc.). I also notice that musl generates some
> empty archives for compatibility reasons, namely the
> lib{crypt,dl,m,pthread,resolv,rt,util,xnet}.a. These are already
> documented in the FAQ [1].
>
> By looking at the code [2], I see that musl's dynamic linker ignores
> dynamic dependencies with names lib{c,pthread,rt,m,dl,util,xnet} and
> this makes sense based on the above.
>
> What doesn't make sense to me is that musl's dynamic linker does not
> ignore dynamic dependencies with names libresolv and libcrypt. Is there
> a reason for this?
I believe the intent was only to reserve names that POSIX explicitly
reserves:
If a directory specified by a -L option contains files with names
starting with any of the strings "libc.", "libl.", "libpthread.",
"libm.", "librt.", "libtrace.", "libxnet.", or "liby.", the
results are unspecified.
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/c99.html
However it looks like the sets don't entirely match up. I'm not sure
of the reason for the mismatch.
The set of "builtin" library names should probably be broken into two
parts: ones that will always be used (c, pthread, m, etc) and ones
that will be used as fallbacks if no file is found (resolv, crypt,
etc.).
Note that the purpose of these built-in names is twofold: (1) it's
part of glibc ABI-compat, for running glibc binaries with their names
in DT_NEEDED, and this role could be moved out with the gcompat
refactor if desired, and (2) supporting programs that (kinda
dubiously) use dlopen with these names to access standard
functionality.
Rich
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