Merge lp://qastaging/~alan-griffiths/mir/fix-1615587 into lp://qastaging/mir

FAILED: Continuous integration, rev:3661
https://mir-jenkins.ubuntu.com/job/mir-ci/1502/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/1869/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/1928
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=vivid+overlay/1919
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial+overlay/1919
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=yakkety/1919
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=yakkety/1893/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial+overlay/1893
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial+overlay/1893/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=yakkety/1893
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=yakkety/1893/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=android,release=vivid+overlay/1893/console
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=android,release=vivid+overlay/1893/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=android,release=vivid+overlay/1893
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=android,release=vivid+overlay/1893/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial+overlay/1893
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial+overlay/1893/artifact/output/*zip*/output.zip

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/1502/rebuild

Two (unrelated) CI failures: lp:1523621 and lp:1586382

FAILED: Continuous integration, rev:3661
https://mir-jenkins.ubuntu.com/job/mir-ci/1503/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/1872/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/1931
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=vivid+overlay/1922
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial+overlay/1922
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=yakkety/1922
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=yakkety/1896
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=yakkety/1896/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial+overlay/1896/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=yakkety/1896
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=yakkety/1896/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=android,release=vivid+overlay/1896/console
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=android,release=vivid+overlay/1896/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=android,release=vivid+overlay/1896
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=android,release=vivid+overlay/1896/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial+overlay/1896
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial+overlay/1896/artifact/output/*zip*/output.zip

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/1503/rebuild

LGTM

Hmm, it is a bit weird actually. I can't remember now why we bother avoiding C++ mangling on code that is strictly not C-compatible anyway. Although I would prefer our driver model was plain C, since it's not, why are we giving it that appearance?

Symbol mangling follows strict rules. So we could just make them proper C++ functions and go searching for the proper mangled C++ symbol names. You only have to figure out what each mangled name is once, and code it once.

It feels like this makes a hack into a worse hack. But not that much worse, so abstain.

While name mangling follows strict rules, they're rules with
architecture specific cases, so if we tried to match on mangled name we
might need to change what symbol we look up depending on the
architecture we're running on.

We could just try and see if we're leaning on any architecture-specific cases. If so, then that's a no. But we might not have any such issues.

*If* we really don't like this (IMO perfectly reasonable) usage we could change the API/ABI design to be C compatible by adding a level of indirection. Vis:

struct GraphicsPlatformEntry
{
virtual mir::UniqueModulePtr<mir::graphics::Platform> create_host_platform(
    std::shared_ptr<mir::options::Option> const& options,
    std::shared_ptr<mir::EmergencyCleanupRegistry> const& emergency_cleanup_registry,
    std::shared_ptr<mir::graphics::DisplayReport> const& report) = 0;
};

// This is the published entry point. NB Ownership is not transferred.
extern "C" GraphicsPlatformEntry* graphics_platform_entry;

// client code does:
  if (void* p = dlvsym(so, "graphics_platform_entry", version))
  {
      return static_cast<GraphicsPlatformEntry*>(p)
        ->create_stub_platform(the_options(), the_emergency_cleanup(), the_display_report());
  }

I don't think that's helpful. Those functions still require C++.

Long term I'd like to see a cleaner driver architecture. Short term, let's land this and fix the bug...

One failure is lp:1563210 but the other...

Why CI why?

16:40:44 running sudo /usr/bin/mir_privileged_tests
16:40:44 [WS-CLEANUP] Deleting project workspace...Running main() from gtest_main.cc
16:40:45 [WS-CLEANUP] done
16:40:45 Finished: ABORTED

https://mir-jenkins.ubuntu.com/job/device-runtests-mir/device_type=krillin/1400/consoleFull

In any case, this MP can only break compilation and the failures are in running tests. So I'll TA and see what happens next.

FAILED: Autolanding.
More details in the following jenkins job:
https://mir-jenkins.ubuntu.com/job/mir-autolanding/533/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/1891/console
    None: https://mir-jenkins.ubuntu.com/job/generic-land-mp/569/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/1951
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=vivid+overlay/1942
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial+overlay/1942
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=yakkety/1942
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=yakkety/1915
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=yakkety/1915/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial+overlay/1915
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial+overlay/1915/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=yakkety/1915/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=android,release=vivid+overlay/1915
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=android,release=vivid+overlay/1915/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=android,release=vivid+overlay/1915
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=android,release=vivid+overlay/1915/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial+overlay/1915
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial+overlay/1915/artifact/output/*zip*/output.zip

^^^
Seems to be the same failure for several branches today...

15:27:29 /usr/include/c++/6/bits/unique_ptr.h:787: error: undefined reference to '_Unwind_Resume'
15:27:29 /usr/include/x86_64-linux-gnu/c++/6/bits/gthr-default.h:778: error: undefined reference to '_Unwind_Resume'
15:27:29 ../../../src/server/glib_main_loop_sources.cpp:316: error: undefined reference to '_Unwind_Resume'
15:27:29 /usr/include/boost/exception/exception.hpp:326: error: undefined reference to '_Unwind_Resume'
15:27:29 collect2: error: ld returned 1 exit status

I see it was already top-approved, but fix is alright by me.