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

[Stefan Hajnoczi <stefanha@redhat.com>]

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.

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(-)

diff --git a/configure b/configure
index 714e75b5d8..5d91d49c7b 100755
--- a/configure
+++ b/configure
@@ -4832,6 +4832,7 @@ if have_backend "dtrace"; then
   trace_backend_stap="no"
   if has 'stap' ; then
     trace_backend_stap="yes"
+    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
 
-- 
2.28.0