Re: [Qemu-devel] [PATCH 0/7] audio: modularize

[Marc-André Lureau]

Hi

On Tue, Mar 6, 2018 at 2:27 PM, Gerd Hoffmann <address@hidden> wrote:
>> >> /home/elmarco/src/qemu/build/x86_64-softmmu/../audio-pa.so: undefined
>> >> symbol: audio_pt_unlock_and_signal
>
>> Fresh directory, cleaned ccache. That didn't help. fwiw, I am
>> compiling on f27, gcc (GCC) 7.3.1 20180130. I'll investigate further
>> if you can't reproduce.
>
> Hmm, working fine here (both rhel-7 and fedora-27 testbuild container, default
> build flags).
>
> The symbol in question should be provided by qemu:
>
> address@hidden ~/projects/qemu/build/fedora# objdump -x audio-pa.so | grep 
> audio_pt_unlock_and_signal
> 0000000000000000         *UND*  0000000000000000              
> audio_pt_unlock_and_signal
> address@hidden ~/projects/qemu/build/fedora# objdump -x 
> x86_64-softmmu/qemu-system-x86_64 | grep audio_pt_unlock_and_signal
> 00000000004735f0 g     F .text  0000000000000067              
> audio_pt_unlock_and_signal
>
> Possibly your linker throws it away, thinking there is no user because of the
> modular drivers?

It's not that, but it works if I build qemu with -rdynamic. dlopen(3):

External  references in the shared object are resolved using the
shared objects in that object's dependency list and any other objects
previously opened with the RTLD_GLOBAL flag.  If the executable
       was linked with the flag "-rdynamic" (or, synonymously,
"--export-dynamic"), then the global symbols in the executable will
also be used to resolve references in a dynamically loaded shared
object.

(If I understand right, there is some magic rules.mk
process-archive-undefs to make sure the used symbols from modules are
always linked in)

Could it be that -rdynamic / --export-dynamic is assumed in our build
system since modules have been added?

yes, it's pulled from /usr/lib64/pkgconfig/gmodule-2.0.pc, but glib
upstream built with meson doesn't have the flag anymore. That's
probably worth fixing in glib:
https://bugzilla.gnome.org/show_bug.cgi?id=794123

We should switch to using gmodule-export-2.0.pc (since 2.6), which is
also broken in meson build.  I'll send a patch for that.

-- 
Marc-André Lureau