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trace: use STAP_SDT_V2 to work around symbol visibility

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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>
This commit is contained in:
Stefan Hajnoczi 2020-11-19 14:14:57 +00:00
parent ff85db769f
commit 4b265c79a8
2 changed files with 9 additions and 2 deletions
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7
configure vendored
View File

@ -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.
QEMU_CFLAGS="$QEMU_CFLAGS -DSTAP_SDT_V2"
fi
fi

4
trace/meson.build
View File

@ -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