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Message-ID: <20200528185325.GF26190@port70.net>
Date: Thu, 28 May 2020 20:53:25 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: Dmitry Samersoff <dms@...ersoff.net>
Cc: musl@...ts.openwall.com, Rich Felker <dalias@...c.org>,
Alexander Scherbatiy <alexander.scherbatiy@...l-sw.com>,
Markus Wichmann <nullplan@....net>
Subject: Re: Shared library loading
* Dmitry Samersoff <dms@...ersoff.net> [2020-05-27 21:10:18 +0300]:
> Hello Alexander,
>
> > The "b" library loading works on my Ubuntu 19.10 and fails on Alpine
> > 3.11.6 with message: > dlopen failed: Error loading shared library
> > liba.so: No such file or
> > directory (needed by /root/load-lib-sample/bin/b/libb.so)
> > Should it work on Alpine with musl libc as well?
>
> 1. You explicitly load library with a path (.../liba.so)
>
> 2. You are explicitly loading another library (.../libb.so)
>
> 3. Linker find liba.so in the appropriate section of libb.so and attempts to
> load it from syspath (LD_LIBRARY_PATH etc)
>
> 4. Linker doesn't find it. Musl return error on this step but glibc and BSD
> go further.
>
> 5. Linker compares short names of already loaded library and the required
> one
this step sounds like implementation specific heuristic
that is not mandated by any spec, so relying on it is
non-portable (and in this case can be dangerous: an
unrelated library may be used because of a name collision)
in principle a dynamic linker can continue even if it
didn't find a library with similar name at all, but that
would be dangerous too.
>
> 6. It matches, so Linker decides to resolve
>
> I didn't find any specification that dictates one or other behavior, so it
> could not be considered as a bug.
i think if there is no spec you should not rely on this
behaviour, i.e. it is a portability bug.
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