libsubcmd: Don't free the usage string

Currently, commands which depend on 'parse_options_subcommand()' don't
show the usage string, and instead show '(null)'

    $ ./perf sched
	Usage: (null)

    -D, --dump-raw-trace  dump raw trace in ASCII
    -f, --force           don't complain, do it
    -i, --input <file>    input file name
    -v, --verbose         be more verbose (show symbol address, etc)

'parse_options_subcommand()' is generally expected to initialise the usage
string, with information in the passed 'subcommands[]' array

This behaviour was changed in:

  230a7a7 ("libsubcmd: Fix parse-options memory leak")

Where the generated usage string is deallocated, and usage[0] string is
reassigned as NULL.

As discussed in [1], free the allocated usage string in the main
function itself, and don't reset usage string to NULL in
parse_options_subcommand

With this change, the behaviour is restored.

    $ ./perf sched
        Usage: perf sched [<options>] {record|latency|map|replay|script|timehist}

           -D, --dump-raw-trace  dump raw trace in ASCII
           -f, --force           don't complain, do it
           -i, --input <file>    input file name
           -v, --verbose         be more verbose (show symbol address, etc)

[1]: https://lore.kernel.org/linux-perf-users/htq5vhx6piet4nuq2mmhk7fs2bhfykv52dbppwxmo3s7du2odf@styd27tioc6e/

Fixes: 230a7a7 ("libsubcmd: Fix parse-options memory leak")
Suggested-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Disha Goel <disgoel@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240904061836.55873-2-adityag@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/subcmd/parse-options.c

@@ -633,10 +633,11 @@ int parse_options_subcommand(int argc, const char **argv, const struct option *o
 			const char *const subcommands[], const char *usagestr[], int flags)
 {
 	struct parse_opt_ctx_t ctx;
-	char *buf = NULL;
 
 	/* build usage string if it's not provided */
 	if (subcommands && !usagestr[0]) {
+		char *buf = NULL;
+
 		astrcatf(&buf, "%s %s [<options>] {", subcmd_config.exec_name, argv[0]);
 
 		for (int i = 0; subcommands[i]; i++) {
@@ -678,10 +679,7 @@ int parse_options_subcommand(int argc, const char **argv, const struct option *o
 			astrcatf(&error_buf, "unknown switch `%c'", *ctx.opt);
 		usage_with_options(usagestr, options);
 	}
-	if (buf) {
-		usagestr[0] = NULL;
-		free(buf);
-	}
+
 	return parse_options_end(&ctx);
 }
 

tools/perf/builtin-kmem.c

@@ -2057,6 +2057,8 @@ int cmd_kmem(int argc, const char **argv)
 
 out_delete:
 	perf_session__delete(session);
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)kmem_usage[0]);
 
 	return ret;
 }

tools/perf/builtin-kvm.c

@@ -2184,5 +2184,8 @@ int cmd_kvm(int argc, const char **argv)
 	else
 		usage_with_options(kvm_usage, kvm_options);
 
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)kvm_usage[0]);
+
 	return 0;
 }

tools/perf/builtin-kwork.c

@@ -2519,5 +2519,8 @@ int cmd_kwork(int argc, const char **argv)
 	} else
 		usage_with_options(kwork_usage, kwork_options);
 
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)kwork_usage[0]);
+
 	return 0;
 }

tools/perf/builtin-lock.c

@@ -2712,6 +2712,9 @@ int cmd_lock(int argc, const char **argv)
 		usage_with_options(lock_usage, lock_options);
 	}
 
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)lock_usage[0]);
+
 	zfree(&lockhash_table);
 	return rc;
 }

tools/perf/builtin-mem.c

@@ -546,5 +546,8 @@ int cmd_mem(int argc, const char **argv)
 	else
 		usage_with_options(mem_usage, mem_options);
 
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)mem_usage[0]);
+
 	return 0;
 }

tools/perf/builtin-sched.c

@@ -3954,5 +3954,8 @@ int cmd_sched(int argc, const char **argv)
 		usage_with_options(sched_usage, sched_options);
 	}
 
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)sched_usage[0]);
+
 	return 0;
 }