Re: [PATCH v2] trace: use STAP_SDT_V2 to work around symbol visibility

[Daniel P . Berrangé]

On Thu, Nov 19, 2020 at 11:27:04AM +0000, Stefan Hajnoczi wrote:
> 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 nice for distros to backport too.

> 
> Cc: Daniel P. Berrangé <berrange@redhat.com>
> Cc: wcohen@redhat.com
> Cc: fche@redhat.com
> Cc: kraxel@redhat.com
> Cc: rjones@redhat.com
> Cc: mrezanin@redhat.com
> Cc: ddepaula@redhat.com
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> v2:
>  * Define STAP_SDT_V2 everywhere [danpb]
> ---
>  configure         | 1 +
>  trace/meson.build | 4 ++--
>  2 files changed, 3 insertions(+), 2 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>



Regards,
Daniel
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