perf tests: Make objdump disassemble zero blocks

Add -z parameter to avoid skipping zero blocks:

 ffffffff816704fe <sysret_check+0x4b>:
 ffffffff816704fe:  7b 34         jnp ffffffff81670534 <sysret_signal+0x1c>
       ...
 ffffffff81670501 <sysret_careful>:
 ffffffff81670501:  0f ba e2 03   bt  $0x3,%edx
 ffffffff81670505:  73 11         jae ffffffff81670518 <sysret_signal>
Signed-off-by: NJan Stancek <jstancek@redhat.com>
Acked-by: NAdrian Hunter <adrian.hunter@intel.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/130c6267fbdb9af506633a9efa06f3269ff5bd2c.1441275982.git.jstancek@redhat.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/code-reading.c

@@ -128,7 +128,7 @@ static int read_via_objdump(const char *filename, u64 addr, void *buf,
 	FILE *f;
 	int ret;
 
-	fmt = "%s -d --start-address=0x%"PRIx64" --stop-address=0x%"PRIx64" %s";
+	fmt = "%s -z -d --start-address=0x%"PRIx64" --stop-address=0x%"PRIx64" %s";
 	ret = snprintf(cmd, sizeof(cmd), fmt, "objdump", addr, addr + len,
 		       filename);
 	if (ret <= 0 || (size_t)ret >= sizeof(cmd))