[PATCH v3 5/6] perf tool: Add fallback stubs for missing dependencies

[Ian Rogers <irogers@google.com>]

Declare stubs directly inside perf.c for commands that have library
dependencies sometimes omitted at build time, such as libtraceevent
(timechart, sched, kmem, lock, trace, kwork) and libelf (probe).

By unconditionally including these commands in the commands[] array,
users will receive a clear, unified warning indicating the missing
dependency instead of the command silently being absent.

Running `perf trace` with libtraceevent missing. Before:
```
perf: 'trace' is not a perf-command. See 'perf --help'.

Did you mean this?
        ftrace
```

After:
```
'trace' command not available: missing libtraceevent devel package at build time.
```

Signed-off-by: Ian Rogers <irogers@google.com>
Assisted-by: Antigravity:gemini-3.1-pro
---
 tools/perf/perf.c | 51 ++++++++++++++++++++++++++++++-----------------
 1 file changed, 33 insertions(+), 18 deletions(-)

diff --git a/tools/perf/perf.c b/tools/perf/perf.c
index 65bdfd71f626..6c5baa285b13 100644
--- a/tools/perf/perf.c
+++ b/tools/perf/perf.c
@@ -7,6 +7,7 @@
  * perf top, perf record, perf report, etc.) are started.
  */
 
+#include <linux/compiler.h>
 #include <errno.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -53,6 +54,38 @@ static void __noreturn usage(const char *err)
 static int use_pager = -1;
 static FILE *debug_fp = NULL;
 
+
+#ifndef HAVE_LIBTRACEEVENT
+#define DECLARE_LIBTRACEEVENT_STUB(_cmd) \
+	int cmd_##_cmd(int argc __always_unused, const char **argv __always_unused) \
+	{ \
+		fprintf(stderr, \
+			"'" #_cmd "' command not available: missing libtraceevent " \
+			"devel package at build time.\n"); \
+		return -1; \
+	}
+
+DECLARE_LIBTRACEEVENT_STUB(timechart)
+DECLARE_LIBTRACEEVENT_STUB(sched)
+DECLARE_LIBTRACEEVENT_STUB(kmem)
+DECLARE_LIBTRACEEVENT_STUB(lock)
+DECLARE_LIBTRACEEVENT_STUB(trace)
+DECLARE_LIBTRACEEVENT_STUB(kwork)
+#endif
+
+#ifndef HAVE_LIBELF_SUPPORT
+#define DECLARE_LIBELF_SUPPORT_STUB(_cmd) \
+	int cmd_##_cmd(int argc __always_unused, const char **argv __always_unused) \
+	{ \
+		fprintf(stderr, \
+			"'" #_cmd "' command not available: missing libelf " \
+			"devel package at build time.\n"); \
+		return -1; \
+	}
+
+DECLARE_LIBELF_SUPPORT_STUB(probe)
+#endif
+
 struct cmd_struct {
 	const char *cmd;
 	int (*fn)(int, const char **);
@@ -76,36 +109,24 @@ static const struct cmd_struct commands[] = {
 	{ "report",	cmd_report,	0 },
 	{ "bench",	cmd_bench,	0 },
 	{ "stat",	cmd_stat,	0 },
-#ifdef HAVE_LIBTRACEEVENT
 	{ "timechart",	cmd_timechart,	0 },
-#endif
 	{ "top",	cmd_top,	0 },
 	{ "annotate",	cmd_annotate,	0 },
 	{ "version",	cmd_version,	0 },
 	{ "script",	cmd_script,	0 },
-#ifdef HAVE_LIBTRACEEVENT
 	{ "sched",	cmd_sched,	0 },
-#endif
-#ifdef HAVE_LIBELF_SUPPORT
 	{ "probe",	cmd_probe,	0 },
-#endif
-#ifdef HAVE_LIBTRACEEVENT
 	{ "kmem",	cmd_kmem,	0 },
 	{ "lock",	cmd_lock,	0 },
-#endif
 	{ "kvm",	cmd_kvm,	0 },
 	{ "test",	cmd_test,	0 },
-#if defined(HAVE_LIBTRACEEVENT)
 	{ "trace",	cmd_trace,	0 },
-#endif
 	{ "inject",	cmd_inject,	0 },
 	{ "mem",	cmd_mem,	0 },
 	{ "data",	cmd_data,	0 },
 	{ "ftrace",	cmd_ftrace,	0 },
 	{ "daemon",	cmd_daemon,	0 },
-#ifdef HAVE_LIBTRACEEVENT
 	{ "kwork",	cmd_kwork,	0 },
-#endif
 };
 
 struct pager_config {
@@ -514,15 +535,9 @@ int main(int argc, const char **argv)
 		argv[0] = cmd;
 	}
 	if (strstarts(cmd, "trace")) {
-#ifndef HAVE_LIBTRACEEVENT
-		fprintf(stderr,
-			"trace command not available: missing libtraceevent devel package at build time.\n");
-		goto out;
-#else
 		setup_path();
 		argv[0] = "trace";
 		return cmd_trace(argc, argv);
-#endif
 	}
 	/* Look for flags.. */
 	argv++;
-- 
2.55.0.966.g6673acef38-goog