tests: acpi: print ASL diff in verbose mode

print ASL difference if there is any when
executing 'make V=1 check'.
Use 'DIFF' environment variable to determine
which diff utility to use and if it's not set
notify user by printing warning that DIFF is
not set if run in verbose mode and there is
difference in ASL.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

tests/bios-tables-test.c

@@ -580,6 +580,22 @@ static void test_acpi_asl(test_data *data)
                         (gchar *)&signature,
                         sdt->asl_file, sdt->aml_file,
                         exp_sdt->asl_file, exp_sdt->aml_file);
+                if (getenv("V")) {
+                    const char *diff_cmd = getenv("DIFF");
+                    if (diff_cmd) {
+                        int ret G_GNUC_UNUSED;
+                        char *diff = g_strdup_printf("%s %s %s", diff_cmd,
+                            exp_sdt->asl_file, sdt->asl_file);
+                        ret = system(diff) ;
+                        g_free(diff);
+                    } else {
+                        fprintf(stderr, "acpi-test: Warning. not showing "
+                            "difference since no diff utility is specified. "
+                            "Set 'DIFF' environment variable to a preferred "
+                            "diff utility and run 'make V=1 check' again to "
+                            "see ASL difference.");
+                    }
+                }
           }
         }
         g_string_free(asl, true);