Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Mittwoch, 9. Februar 2022 14:33:25 CET Akihiko Odaki wrote:
> > I like the idea of switching it to __attribute__((weak)). I should note
> > that I'm not sure that I can actually fully test this out since I'm
> > getting stuck with the linker noting my undefined fake function during
> > the build, but the idea does make logical sense to me for the future fail
> > case and the happy case builds again when implemented with actual
> > pthread_fchdir_np:
> > 
> > [1075/2909] Linking target qemu-nbd
> > FAILED: qemu-nbd
> > cc -m64 -mcx16  -o qemu-nbd qemu-nbd.p/qemu-nbd.c.o -Wl,-dead_strip_dylibs
> > -Wl,-headerpad_max_install_names -Wl,-undefined,error -Wl,-force_load
> > libblockdev.fa -Wl,-force_load libblock.fa -Wl,-force_load libcrypto.fa
> > -Wl,-force_load libauthz.fa -Wl,-force_load libqom.fa -Wl,-force_load
> > libio.fa -fstack-protector-strong
> > -Wl,-rpath,/usr/local/Cellar/gnutls/3.7.3/lib
> > -Wl,-rpath,/usr/local/Cellar/pixman/0.40.0/lib libqemuutil.a
> > libblockdev.fa libblock.fa libcrypto.fa libauthz.fa libqom.fa libio.fa
> > @block.syms /usr/local/Cellar/gnutls/3.7.3/lib/libgnutls.dylib -lutil
> > -L/usr/local/Cellar/glib/2.70.3/lib -L/usr/local/opt/gettext/lib
> > -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lintl
> > -L/usr/local/Cellar/glib/2.70.3/lib -L/usr/local/opt/gettext/lib
> > -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lintl -lm
> > -L/usr/local/Cellar/glib/2.70.3/lib -L/usr/local/opt/gettext/lib
> > -lgmodule-2.0 -lglib-2.0 -lintl
> > /usr/local/Cellar/pixman/0.40.0/lib/libpixman-1.dylib -lz -lxml2
> > -framework CoreFoundation -framework IOKit -lcurl
> > -L/usr/local/Cellar/glib/2.70.3/lib -L/usr/local/opt/gettext/lib
> > -lgmodule-2.0 -lglib-2.0 -lintl -lbz2
> > /usr/local/Cellar/libssh/0.9.6/lib/libssh.dylib -lpam> 
> > Undefined symbols for architecture x86_64:
> >   "_pthread_fchdir_npfoo", referenced from:
> >       _qemu_mknodat in libblockdev.fa(os-posix.c.o)
> > 
> > ld: symbol(s) not found for architecture x86_64
> > clang: error: linker command failed with exit code 1 (use -v to see
> > invocation) ninja: build stopped: subcommand failed.
> > make[1]: *** [run-ninja] Error 1
> > make: *** [all] Error 2
> > 
> > With that caveat re testing in mind, unless there's another recommended
> > path forward, I think it makes sense to stick with __attribute__((weak))
> > and prepare v6 which incorporates this and all the other feedback from
> > this round.
> __attribute__((weak_import)), which explicitly marks the function as
> external, is more appropriate here. It is feature-equivalent with the
> availability attribute when the minimum deployment target is lower
> than the version which introduced the function.

Thanks for chiming in on this macOS issue Akihiko!

Are you sure that "weak_import" is still the preferred way? From behaviour PoV 
I do not see any difference at all. I can't even tell what the intended 
difference was, and QEMU currently only seems to use "weak" in the entire code 
base.

Googling around, "weak_import" seems to be required on ancient OS X versions 
only and that it's now deprecated in favour of the more common "weak", no?

Best regards,
Christian Schoenebeck