[Bug 1916705] Re: glib2.0 >=2.67.3 breaks include from an extern C context

Launchpad Bug Tracker 1916705 at bugs.launchpad.net
Mon Mar 22 07:38:19 UTC 2021 

** Merge proposal linked:
   https://code.launchpad.net/~paelzer/ubuntu/+source/qemu/+git/qemu/+merge/399966

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Title:
  glib2.0 >=2.67.3 breaks include from an extern C context

Status in glib2.0 package in Ubuntu:
  Fix Released
Status in open-vm-tools package in Ubuntu:
  Fix Released
Status in qemu package in Ubuntu:
  Fix Released
Status in ukui-control-center package in Ubuntu:
  Triaged
Status in wireshark package in Ubuntu:
  Fix Released

Bug description:
  qemu now breaks in Hirsute (it didn't 23h ago)
  Broken:
  https://launchpadlibrarian.net/524654684/buildlog_ubuntu-hirsute-amd64.qemu_1%3A5.2+dfsg-6ubuntu1_BUILDING.txt.gz

  Good before:
  https://launchpad.net/~ci-train-ppa-service/+archive/ubuntu/4471/+packages

  Error:

  ../../disas/arm-a64.cc
  In file included from /usr/include/glib-2.0/glib/gmacros.h:241,
                   from /usr/lib/x86_64-linux-gnu/glib-2.0/include/glibconfig.h:9,
                   from /usr/include/glib-2.0/glib/gtypes.h:32,
                   from /usr/include/glib-2.0/glib/galloca.h:32,
                   from /usr/include/glib-2.0/glib.h:30,
                   from /<<BUILDDIR>>/qemu-5.2+dfsg/include/glib-compat.h:32,
                   from /<<BUILDDIR>>/qemu-5.2+dfsg/include/qemu/osdep.h:126,
                   from ../../disas/arm-a64.cc:21:
  /usr/include/c++/10/type_traits:56:3: error: template with C linkage
     56 |   template<typename _Tp, _Tp __v>
        |   ^~~~~~~~
  ../../disas/arm-a64.cc:20:1: note: ‘extern "C"’ linkage started here
     20 | extern "C" {
        | ^~~~~~~~~~

  Also in disas/nanomips.cpp, ...

  And indeed disas/arm-a64.cc has:
   20 extern "C" {
   21 #include "qemu/osdep.h"
   22 #include "disas/dis-asm.h"
   23 }

  Through the chain of headers as reported above this gets to the templates
  in /usr/include/c++/10/type_traits which fails due to that.

  So C++ constructs within a C scope which is this bug.

  Upstream qemu has not recently changed yet for this.
  The code is the same since 2016 via commit e78490c44: "disas/arm-a64.cc:
  Include osdep.h first" by Peter Maydell.

  But what was different before to break it now?
  To find that I was comparing Hirsute vs Hirsute-proposed ...

  It is indeed failing in -proposed but working in hirsute-release.

  10.2.1-20ubuntu1 : bad

  repro in broken build:
  $ cd /root/qemu-5.2+dfsg/b/qemu
  $ c++ -Ilibcommon.fa.p -I. -I../.. -Iqapi -Itrace -Iui -Iui/shader -I/usr/include/pixman-1 -I/usr/include/virgl -I/usr/include/libpng16 -I/usr/include/spice-server -I/usr/include/spice-1 -I/usr/include/libusb-1.0 -I/usr/include/libmount -I/usr/include/blkid -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/gio-unix-2.0 -I/usr/include/cacard -I/usr/include/nss -I/usr/include/nspr -I/usr/include/PCSC -I/usr/include/slirp -fdiagnostics-color=auto -pipe -Wall -Winvalid-pch -Wnon-virtual-dtor -std=gnu++11 -O2 -g -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -U_FORTIFY_SOURCE -m64 -mcx16 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -Wundef -Wwrite-strings -fno-strict-aliasing -fno-common -fwrapv -g -O2 -ffile-prefix-map=/root/qemu-5.2+dfsg=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -Wtype-limits -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers -Wempty-body -Wendif-labels -Wexpansion-to-defined -Wno-missing-include-dirs -Wno-shift-negative-value -Wno-psabi -fstack-protector-strong -isystem /root/qemu-5.2+dfsg/linux-headers -isystem linux-headers -iquote /root/qemu-5.2+dfsg/tcg/i386 -iquote . -iquote /root/qemu-5.2+dfsg -iquote /root/qemu-5.2+dfsg/accel/tcg -iquote /root/qemu-5.2+dfsg/include -iquote /root/qemu-5.2+dfsg/disas/libvixl -pthread -fPIE -DSTRUCT_IOVEC_DEFINED -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=600 -DNCURSES_WIDECHAR -MD -MQ libcommon.fa.p/disas_nanomips.cpp.o -MF libcommon.fa.p/disas_nanomips.cpp.o.d -o libcommon.fa.p/disas_nanomips.cpp.o -c ../../disas/nanomips.cpp

  With that I have a test env...

  Doko asked me to test
  https://launchpad.net/ubuntu/+source/gcc-10/10.2.1-19ubuntu1/+build/20995220/+files/g++-10_10.2.1-19ubuntu1_amd64.deb
  That fails as well, but also good as well as bad case have 10.10.2.1-20ubuntu1
  It must be something else.

  The difference were ~340 packages I was upgrading them to spot what broke it.
  I eventually found glib 2.66 -> 2.67 to break it.

  libglib2.0-0/hirsute-proposed 2.67.4-1 amd64 [upgradable from: 2.66.4-1]
  libglib2.0-bin/hirsute-proposed 2.67.4-1 amd64 [upgradable from: 2.66.4-1]
  libglib2.0-data/hirsute-proposed 2.67.4-1 all [upgradable from: 2.66.4-1]
  libglib2.0-dev-bin/hirsute-proposed 2.67.4-1 amd64 [upgradable from: 2.66.4-1]
  libglib2.0-dev/hirsute-proposed 2.67.4-1 amd64 [upgradable from: 2.66.4-1]

  Old:
  /*
   * We can only use __typeof__ on GCC >= 4.8, and not when compiling C++. Since
   * __typeof__ is used in a few places in GLib, provide a pre-processor symbol
   * to factor the check out from callers.
   *
   * This symbol is private.
   */
  #undef g_has_typeof
  #if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8)) && !defined(__cplusplus)
  #define g_has_typeof
  #endif

  New:
  /*
   * We can only use __typeof__ on GCC >= 4.8, and not when compiling C++. Since
   * __typeof__ is used in a few places in GLib, provide a pre-processor symbol
   * to factor the check out from callers.
   *
   * This symbol is private.
   */
  #undef glib_typeof
  #if !defined(__cplusplus) && \
       ((defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8))) || \
        defined(__clang__))
  #define glib_typeof(t) __typeof__ (t)
  #elif defined(__cplusplus) && __cplusplus >= 201103L
  /* C++11 decltype() is close enough for our usage */
  #include <type_traits>                         <--- THIS IS WHAT BREAKS US
  #define glib_typeof(t) typename std::remove_reference<decltype (t)>::type
  #define glib_typeof_2_68
  #endif

  On the glib side this is due to:
  https://gitlab.gnome.org/GNOME/glib/-/issues/2331
  Also related:
  https://gitlab.gnome.org/GNOME/glib/-/merge_requests/1935
  https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/J3P4TRHLWNDIKXF76OLYZNAPTABCZ3U5/#7LXFUDBBBIT23FE44QJYWX3I7U4EHW6M

  Qemu try to fix/discussion at:
  https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg07294.html
  This won't be the final solution, but it gets things going for the time being.

  glib try to fix (also seems not to be ok for upstream, but would get everything going for now). Thanks Laney btw:
  https://gitlab.gnome.org/iainl/glib/-/commit/b865b76c01a35fb8dbffb9bc2907acf341a31aba

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