MB-32598: Reduce the number of times to invoke gdb

The breakpad tests used to invoke gdb several times to inspect
various pieces of the minidump file. Unfortunately the startup
cost of gdb seems to be relatively high so we should try to
reduce the number of times it is invoked.

To work around this we'll invoke gdb a single time, and execute
all of the commands in a single batch. To make it easy to figure
out the result from each command we invoke 'show print pretty'
between each command so that we can easily use the result of
that command to split the output.

Change-Id: Ie2fd605c589753d695caa8fd883cc0a3db13a4f6
Reviewed-on: http://review.couchbase.org/103586
Tested-by: Build Bot <[email protected]>
Reviewed-by: Dave Rigby <[email protected]>

Author: trondn

tests/breakpad_test.py

@@ -216,15 +216,28 @@ def target():
             os.remove(minidump)
             cleanup_and_exit(7)
 
+        # To avoid invoking gdb multiple times, lets collect all of the
+        # information in a single pass. To make it easy to figure out
+        # the output from each command, run 'show print pretty' and use
+        # the expected output from that command to split the data
+        logging.info('GDB: Collect information from the minidump file')
+        gdb_output = invoke_gdb(gdb_exe, memcached_exe, core_file,
+                                ['set print pretty off',
+                                 'show print pretty',
+                                 'info shared',
+                                 'show print pretty',
+                                 'backtrace',
+                                 'show print pretty',
+                                 'x/x $sp'])
+        gdb_output = gdb_output.split("Pretty formatting of structures is off.")
+
         # Check for shared library information, and symbols successfully ead
         # (needed for any useful backtraces).
         # Shared libraries may change over time, but we explicitly asked for
         # crash_engine.so in the config so we should have that.
         logging.info('GDB: Checking for shared library information')
-        gdb_output = invoke_gdb(gdb_exe, memcached_exe, core_file,
-                                ['info shared'])
         m = re.search("^0x[0-9a-f]+\s+0x[0-9a-f]+\s+(\w+)\s+([^\s]+crash_engine\.so$)",
-                      gdb_output, re.MULTILINE)
+                      gdb_output[1], re.MULTILINE)
         if not m:
             logging.error("FAIL - GDB unable to show information for " +
                   "crash_engine.so shared library.")
@@ -240,9 +253,7 @@ def target():
         # particular trace. Instead we check that all frames but the first have
         # a useful-looking symbol (and not just a random address.)
         logging.info('GDB: Checking for sensible backtrace')
-        gdb_output = invoke_gdb(gdb_exe, memcached_exe, core_file,
-                                ['backtrace'])
-        lines = gdb_output.splitlines()
+        lines = gdb_output[2].splitlines()
 
         # Discard all those lines before the stacktrace
         backtrace = [i for i in lines if re.match('#\d+', i)]
@@ -274,9 +285,7 @@ def target():
         # Check we can read stack memory. Another tricky one as again we have
         # no idea where we crashed. Just ensure that we get *something* back
         logging.info('GDB: Checking for readable stack memory')
-        gdb_output = invoke_gdb(gdb_exe, memcached_exe, core_file,
-                                ['x/x $sp'])
-        m = re.search('(0x[0-9a-f]+):\s(0x[0-9a-f]+)?', gdb_output)
+        m = re.search('(0x[0-9a-f]+):\s(0x[0-9a-f]+)?', gdb_output[3])
         if not m:
             logging.error("FAIL - GDB failed to output memory disassembly when " +
                   "attempting to examine stack.")