libqemuutil

[Markus Armbruster]

I rebased my "[PATCH v6 00/10] Configurable policy for handling
deprecated interfaces" to master, and it surprisingly fails to link
several utility programs.  Here's the first error:

    gcc  -o tests/bench/benchmark-crypto-hmac 
tests/bench/benchmark-crypto-hmac.p/benchmark-crypto-hmac.c.o -Wl,--as-needed 
-Wl,--no-undefined -pie -Wl,--whole-archive libcrypto.fa libauthz.fa libqom.fa 
-Wl,--no-whole-archive -Wl,--warn-common -Wl,-z,relro -Wl,-z,now -m64 
-fstack-protector-strong -Wl,--start-group libqemuutil.a 
subprojects/libvhost-user/libvhost-user-glib.a 
subprojects/libvhost-user/libvhost-user.a libcrypto.fa libauthz.fa libqom.fa 
-pthread -lgthread-2.0 -lglib-2.0 -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lgio-2.0 
-lgobject-2.0 -lglib-2.0 -lgnutls -lutil -lm -lgthread-2.0 -lglib-2.0 -lnettle 
-lgnutls -lpam -Wl,--end-group
    /usr/bin/ld: libqemuutil.a(util_main-loop.c.o): in function 
`qemu_set_fd_handler':
    /work/armbru/qemu/bld-x86/../util/main-loop.c:581: multiple definition of 
`qemu_set_fd_handler'; 
libqemuutil.a(stubs_set-fd-handler.c.o):/work/armbru/qemu/bld-x86/../stubs/set-fd-handler.c:8:
 first defined here
    collect2: error: ld returned 1 exit status

Both master and PATCH 01 still link fine, PATCH 02 doesn't.  PATCH 02
doesn't go anywhere near qemu_set_fd_handler().

Turns out libqemuutil.a contains two definitions of
qemu_set_fd_handler().  In master:

    $ nm --defined-only libqemuutil.a | awk '/:$/ { f=$0 } / 
qemu_set_fd_handler/ { if (f) { print f; f="" } print $0 }'
    util_main-loop.c.o:
    00000000000007fe T qemu_set_fd_handler
    stubs_set-fd-handler.c.o:
    0000000000000000 T qemu_set_fd_handler

This is obviously unhealthy.

I suspect the linker happens to pick the one that makes things work,
until something in my patch makes it pick the other one.

Is qemu_set_fd_handler() the only one?  Nope:

    $ nm --defined-only bld-x86/libqemuutil.a | awk '/ T / { print $NF }' | 
sort | uniq -c | grep -v '^ *1 '
          2 qemu_set_fd_handler
          2 yank_generic_iochannel
          2 yank_register_function
          2 yank_register_instance
          2 yank_unregister_function
          2 yank_unregister_instance

I didn't run into this issue when I posted my series last Friday.  The
issue now blocks its merge, and today is the soft freeze.  Help!