perf build: Improve error message for old/missing clang

clang is required to build perf with BUILD_BPF_SKEL=1. Improve the
error message to highlight that:

  1) clang could be either missing or too old;
  2) clang is only required with BUILD_BPF_SKEL=1.

Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Song Liu <song@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 406a9519145e55487025660376b65ccb0750327f..829e0498bd510616d5c7022beb4cb67e7266e751 100644 (file)
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -635,7 +635,7 @@ endif
 ifdef BUILD_BPF_SKEL
   $(call feature_check,clang-bpf-co-re)
   ifeq ($(feature-clang-bpf-co-re), 0)
-    dummy := $(error Error: clang too old. Please install recent clang)
+    dummy := $(error Error: clang too old/not installed. Please install recent clang to build with BUILD_BPF_SKEL)
   endif
   $(call detected,CONFIG_PERF_BPF_SKEL)
   CFLAGS += -DHAVE_BPF_SKEL