[PATCH v2] tools/perf: Fix perf test 7 Simple expression parser

[Thomas Richter]

Some platforms do not have CPU die support, for example s390.
Commit fdf1e29b6118 ("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
 #
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Fixes: fdf1e29b6118 ("perf expr: Add metric literals for topology.")

Signed-off-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
Acked-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/tests/expr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/tests/expr.c b/tools/perf/tests/expr.c
index c895de481fe1..9356d90bf8db 100644
--- a/tools/perf/tests/expr.c
+++ b/tools/perf/tests/expr.c
@@ -169,7 +169,8 @@ 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)
+		TEST_ASSERT_VAL("#num_dies >= #num_packages", num_dies >= num_packages);
 
 	/*
 	 * Source count returns the number of events aggregating in a leader
-- 
2.31.1