perf test: Fix 'Simple expression parser' test on arch without CPU die topology info

Some platforms do not have CPU die support, for example s390.

Commit
Cc: Ian Rogers <irogers@google.com>
Fixes: fdf1e29b ("perf expr: Add metric literals for topology.")
fails on s390:

  # perf test -Fv 7
    ...
  # FAILED tests/expr.c:173 #num_dies >= #num_packages
    ---- end ----
    Simple expression parser: FAILED!
  #

Investigating this issue leads to these functions:

 build_cpu_topology()
   +--> has_die_topology(void)
        {
           struct utsname uts;

           if (uname(&uts) < 0)
                  return false;
           if (strncmp(uts.machine, "x86_64", 6))
                  return false;
           ....
        }

which always returns false on s390. The caller build_cpu_topology()
checks has_die_topology() return value. On false the the struct
cpu_topology::die_cpu_list is not contructed and has zero entries. This
leads to the failing comparison: #num_dies >= #num_packages.  s390 of
course has a positive number of packages.

Fix this and check if the function build_cpu_topology() did build up
a die_cpus_list. The number of entries in this list should be larger
than 0. If the number of list element is zero, the die_cpus_list has
not been created and the check in function test__expr():

    TEST_ASSERT_VAL("#num_dies >= #num_packages", \
		    num_dies >= num_packages)

always fails.

Output after:

  # perf test -Fv 7
   7: Simple expression parser                                        :
   --- start ---
   division by zero
   syntax error
   ---- end ----
   Simple expression parser: Ok
  #

Fixes: fdf1e29b ("perf expr: Add metric literals for topology.")
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: http://lore.kernel.org/lkml/20211129112339.3003036-1-tmricht@linux.ibm.com
[ Added comment in the added 'if (num_dies)' line about architectures not having die topology ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/expr.c

@@ -169,7 +169,9 @@ static int test__expr(struct test_suite *t __maybe_unused, int subtest __maybe_u
 	TEST_ASSERT_VAL("#num_dies", expr__parse(&num_dies, ctx, "#num_dies") == 0);
 	TEST_ASSERT_VAL("#num_cores >= #num_dies", num_cores >= num_dies);
 	TEST_ASSERT_VAL("#num_packages", expr__parse(&num_packages, ctx, "#num_packages") == 0);
-	TEST_ASSERT_VAL("#num_dies >= #num_packages", num_dies >= num_packages);
+
+	if (num_dies) // Some platforms do not have CPU die support, for example s390
+		TEST_ASSERT_VAL("#num_dies >= #num_packages", num_dies >= num_packages);
 
 	/*
 	 * Source count returns the number of events aggregating in a leader