Bug#915566: libsystemd-dev: static library not provided

[Simon McVittie]

On Sat, 31 Aug 2019 at 00:31:12 +0200, Michael Biebl wrote:
> Simon, have you tried building systemd with -Dstatic-libsystemd=true
> -Dstatic-libudev=true ? Does this produce something useful?

I haven't tried it.

> Upstream doesn't seem to be too keen on supporting static builds, so if
> we divert here downstream, I'd be interested if there is actual demand
> from users of such a libsystemd.a or if this all mostly hyphothetical.

This is hypothetical, and if you want to say "no" and mark this as wontfix
or close it, that's fine; but I wanted to ask the question rather than
making an assumption about the likely answer.

The context is that I have been trying to write autopkgtests for -dev
packages, on the basis that if we have a feature, we should prove that
it works; and I've found that when a library in the dependency stack is
shared-only (for example libdbus depends on libsystemd), it is not at
all obvious how to link statically to the depending library (libdbus).
The obvious rune

    cc -Wl,--no-as-needed -static -otest test.c `pkg-config --static --cflags --libs dbus-1`

fails, because there is no libsystemd.a to link.

(I'm using -Wl,--no-as-needed because the test.c that I'm currently
playing with doesn't actually call into libdbus, and I don't want to
invalidate the test results by having the linker decide not to link
libdbus or libsystemd after all; in real autopkgtests I try to call at
least a harmless function like dbus_get_version().)

It is still possible to link libsystemd and libc dynamically, but libdbus
statically, with something like

    cc -Wl,--no-as-needed -otest test.c `pkg-config --static --cflags --libs dbus-1 | perl -pe 's,(^|\s)-ldbus-1(\s|$), /usr/lib/x86_64-linux-gnu/libdbus-1\.a ,'`

but that requires you to know the physical location of the library, and
once you have to rely on *anything* with shared linkage, you might as
well bundle *everything* with shared linkage (and -Wl,-rpath,'$ORIGIN'
or similar), at which point you've gained nothing from static libraries.

That would point towards a conclusion that if a library like libdbus
has shared-only dependencies like libsystemd, then libdbus should also
become shared-only, which would reduce the size of the binary archive
and the time taken to compile, but would harm the possibly-hypothetical
use cases that are the reason Policy tells us to build static libraries?

Another possible direction would be to disable static libraries in
general, except in cases where a bug report indicates that a real user
genuinely wants them (and has a recipe for testing that they work).

    smcv