[Qemu-commits] [qemu/qemu] 4b265c: trace: use STAP_SDT_V2 to work around symbol visib...

[Peter Maydell]

  Branch: refs/heads/staging
  Home:   https://github.com/qemu/qemu
  Commit: 4b265c79a85bb35abe19aacea6954c1616521639
      
https://github.com/qemu/qemu/commit/4b265c79a85bb35abe19aacea6954c1616521639
  Author: Stefan Hajnoczi <stefanha@redhat.com>
  Date:   2020-11-19 (Thu, 19 Nov 2020)

  Changed paths:
    M configure
    M trace/meson.build

  Log Message:
  -----------
  trace: use STAP_SDT_V2 to work around symbol visibility

QEMU binaries no longer launch successfully with recent SystemTap
releases. This is because modular QEMU builds link the sdt semaphores
into the main binary instead of into the shared objects where they are
used. The symbol visibility of semaphores is 'hidden' and the dynamic
linker prints an error during module loading:

  $ ./configure --enable-trace-backends=dtrace --enable-modules ...
  ...
  Failed to open module: 
/builddir/build/BUILD/qemu-4.2.0/s390x-softmmu/../block-curl.so: undefined 
symbol: qemu_curl_close_semaphore

The long-term solution is to generate per-module dtrace .o files and
link them into the module instead of the main binary.

In the short term we can define STAP_SDT_V2 so dtrace(1) produces a .o
file with 'default' symbol visibility instead of 'hidden'. This
workaround is small and easier to merge for QEMU 5.2 and downstream
backports.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1898700
Cc: wcohen@redhat.com
Cc: fche@redhat.com
Cc: kraxel@redhat.com
Cc: rjones@redhat.com
Cc: ddepaula@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Miroslav Rezanina <mrezanin@redhat.com>
Message-id: 20201119141457.844452-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>


  Commit: 7fbd7e710323c8f4c5f6a38a8ae0e6726b5a4599
      
https://github.com/qemu/qemu/commit/7fbd7e710323c8f4c5f6a38a8ae0e6726b5a4599
  Author: Peter Maydell <peter.maydell@linaro.org>
  Date:   2020-11-19 (Thu, 19 Nov 2020)

  Changed paths:
    M configure
    M trace/meson.build

  Log Message:
  -----------
  Merge remote-tracking branch 
'remotes/stefanha-gitlab/tags/tracing-pull-request' into staging

Pull request

Fix --enable-modules --enable-trace-backends=dtrace with recent SystemTap
releases.

# gpg: Signature made Thu 19 Nov 2020 16:47:33 GMT
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha-gitlab/tags/tracing-pull-request:
  trace: use STAP_SDT_V2 to work around symbol visibility

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>


Compare: https://github.com/qemu/qemu/compare/ff85db769ffd...7fbd7e710323