perf check: Allow showing a tip for opt-in features not built into perf

Ingo reported that it was difficult to understand why libunwind support
didn't link even when he had the usual libunwind-dev files installed in
his machine.

This is because libunwind became opt-in, the user has to use
LIBUNWIND=1, as it was deemed stalled in its development/unsuitable for
use with perf, IIRC, and so we better use the elfutils equivalent
routine that we also supported for ages.

But the build message still printed:

  Auto-detecting system features:
  ...                                   libdw: [ on  ]
  ...                                   glibc: [ on  ]
  <SNIP>
  ...                               libcrypto: [ on  ]
  ...                               libunwind: [ OFF ]
  <SNIP>

Which is confusing, so allow for having a tip when 'perf version
--build-options' is used, and variants with 'perf check feature':

  $ perf version --build-options | grep libunwind
             libunwind: [ OFF ]  # HAVE_LIBUNWIND_SUPPORT ( tip: Deprecated, use LIBUNWIND=1 and install libunwind-dev[el] to build with it )
  $
  $ perf check feature libunwind
             libunwind: [ OFF ]  # HAVE_LIBUNWIND_SUPPORT ( tip: Deprecated, use LIBUNWIND=1 and install libunwind-dev[el] to build with it )
  $

The next patches will remove the opt-in libunwind FEATURES_DISPLAY.

Reported-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Ingo Molnar <mingo@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/Z--pWmTHGb62_83e@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 14 insertions, 2 deletions

diff --git a/tools/perf/builtin-check.c b/tools/perf/builtin-check.c
index a451fa25f50d..a5b76ff5988c 100644
--- a/tools/perf/builtin-check.c
+++ b/tools/perf/builtin-check.c
@@ -27,6 +27,12 @@ static const char *check_feature_usage[] = {
 	.macro = #macro_,                  \
 	.is_builtin = IS_BUILTIN(macro_) }
 
+#define FEATURE_STATUS_TIP(name_, macro_, tip_) { \
+	.name = name_,				  \
+	.macro = #macro_,			  \
+	.tip = tip_,				  \
+	.is_builtin = IS_BUILTIN(macro_) }
+
 struct feature_status supported_features[] = {
 	FEATURE_STATUS("aio", HAVE_AIO_SUPPORT),
 	FEATURE_STATUS("bpf", HAVE_LIBBPF_SUPPORT),
@@ -48,7 +54,7 @@ struct feature_status supported_features[] = {
 	FEATURE_STATUS("libpython", HAVE_LIBPYTHON_SUPPORT),
 	FEATURE_STATUS("libslang", HAVE_SLANG_SUPPORT),
 	FEATURE_STATUS("libtraceevent", HAVE_LIBTRACEEVENT),
-	FEATURE_STATUS("libunwind", HAVE_LIBUNWIND_SUPPORT),
+	FEATURE_STATUS_TIP("libunwind", HAVE_LIBUNWIND_SUPPORT, "Deprecated, use LIBUNWIND=1 and install libunwind-dev[el] to build with it"),
 	FEATURE_STATUS("lzma", HAVE_LZMA_SUPPORT),
 	FEATURE_STATUS("numa_num_possible_cpus", HAVE_LIBNUMA_SUPPORT),
 	FEATURE_STATUS("zlib", HAVE_ZLIB_SUPPORT),
@@ -78,7 +84,12 @@ void feature_status__printf(const struct feature_status *feature)
 
 	printf("%22s: ", name);
 	on_off_print(status);
-	printf("  # %s\n", macro);
+	printf("  # %s", macro);
+
+	if (!feature->is_builtin && feature->tip)
+		printf(" ( tip: %s )", feature->tip);
+
+	putchar('\n');
 }
 
 /**
diff --git a/tools/perf/builtin.h b/tools/perf/builtin.h
index 7db7bc054f6e..40c4078c295f 100644
--- a/tools/perf/builtin.h
+++ b/tools/perf/builtin.h
@@ -5,6 +5,7 @@
 struct feature_status {
 	const char *name;
 	const char *macro;
+	const char *tip;
 	int is_builtin;
 };