Re: dlsym(handle) may search in unrelated libraries

[Szabolcs Nagy <nsz@port70.net>]

* A. Wilcox <awilfox@adelielinux.org> [2019-02-08 04:19:32 -0600]:
> On Feb 7, 2019, at 10:54 AM, Rich Felker <dalias@libc.org> wrote:
> > 
> > However, a depth-first list of dependencies is also needed to solve the longstanding ctor-order issue discussed in several past threads (which I can look up if search doesn't turn them up for you). This is not a requirement of POSIX (which doesn't even have ctors), but it's a reasonable expectation we currently get wrong and I think it might be specified in ELF or some related sysv "standards".
> 
> 
> It is part of the ELF 1.2 standard and is not only required by GLib, but also Nouveau, gtk-doc, some Qt apps, and others.

note, that the ctor order in c++ is undefined across translation
units so if a c++ application relies on it that's a bug: the c++
ctor concept does not necessarily map directly to the elf
initialization function concept on an elf platform so the elf
spec does not save them.

in the elf context, relying on DT_NEEDED for ctor ordering
across libraries means that static linking is broken since
then there is no DT_NEEDED.

so these packages should be fixed independently of musl
(assuming they want to be portable or at least static linkable).

that said, lot of libraries do rely on dependency based ctor
ordering even beyond the elf guarantees (glibc and solaris
dynamic linkers considers relocations on top of DT_NEEDED to
establish dependencies between dsos) and some applications
have dependency cycles which of course is impossible to get
right but glibc tries to keep the ctor order deterministic
in some way even in the presence of dlopen during init.

originally dynamic linkers did exactly what musl did, there
is a nice overview how the complexity evolved:
https://blogs.oracle.com/solaris/init-and-fini-processing-who-designed-this-v2

> More info, including the spec citation, example failures, and the musl ML thread, can be found on our BTS:
> 
> https://bts.adelielinux.org/show_bug.cgi?id=11
> 
> Best,
> —arw 
> 
> 
> --
> A. Wilcox (Sent from my iPhone - not signed)
> Project Lead, Adélie Linux
> https://adelielinux.org