On 11/19/20 3:14 PM, 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 downstream
> backports.
>
> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1898700
> Cc: wco...@redhat.com
> Cc: f...@redhat.com
> Cc: kra...@redhat.com
> Cc: rjo...@redhat.com
> Cc: ddepa...@redhat.com
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> Reviewed-by: Daniel P. Berrangé <berra...@redhat.com>
> Reviewed-by: Philippe Mathieu-Daudé <phi...@redhat.com>
> Reviewed-by: Miroslav Rezanina <mreza...@redhat.com>
> ---
> v3:
> * Tweak commit description for clarity [danpb]
> * Add Buglink tag
> * Add explanation comment into ./configure [Philippe]
> * Add Reviewed-by tags
> v2:
> * Define STAP_SDT_V2 everywhere [danpb]
> ---
> configure | 7 +++++++
> trace/meson.build | 4 ++--
> 2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/configure b/configure
> index 714e75b5d8..796cec14de 100755
> --- a/configure
> +++ b/configure
> @@ -4832,6 +4832,13 @@ if have_backend "dtrace"; then
> trace_backend_stap="no"
> if has 'stap' ; then
> trace_backend_stap="yes"
> +
> + # Workaround to avoid dtrace(1) producing a file with 'hidden' symbol
> + # visibility. Define STAP_SDT_V2 to produce 'default' symbol visibility
> + # instead. QEMU --enable-modules depends on this because the SystemTap
> + # semaphores are linked into the main binary and not the module's shared
> + # object.
Thanks!
> + QEMU_CFLAGS="$QEMU_CFLAGS -DSTAP_SDT_V2"
> fi
> fi
>
> diff --git a/trace/meson.build b/trace/meson.build
> index d5fc45c628..843ea14495 100644
> --- a/trace/meson.build
> +++ b/trace/meson.build
> @@ -38,13 +38,13 @@ foreach dir : [ '.' ] + trace_events_subdirs
> trace_dtrace_h = custom_target(fmt.format('trace-dtrace', 'h'),
> output: fmt.format('trace-dtrace', 'h'),
> input: trace_dtrace,
> - command: [ 'dtrace', '-o', '@OUTPUT@',
> '-h', '-s', '@INPUT@' ])
> + command: [ 'dtrace', '-DSTAP_SDT_V2',
> '-o', '@OUTPUT@', '-h', '-s', '@INPUT@' ])
> trace_ss.add(trace_dtrace_h)
> if host_machine.system() != 'darwin'
> trace_dtrace_o = custom_target(fmt.format('trace-dtrace', 'o'),
> output: fmt.format('trace-dtrace', 'o'),
> input: trace_dtrace,
> - command: [ 'dtrace', '-o', '@OUTPUT@',
> '-G', '-s', '@INPUT@' ])
> + command: [ 'dtrace', '-DSTAP_SDT_V2',
> '-o', '@OUTPUT@', '-G', '-s', '@INPUT@' ])
> trace_ss.add(trace_dtrace_o)
> endif
>
>
