[PATCH] perf build: Add warning for when vmlinux.h generation fails

[Ian Rogers]

The warning advises on the NO_BPF_SKEL=1 option.

Suggested-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/Makefile.perf | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index ed6b6a070f79..48aba186ceb5 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -1072,7 +1072,11 @@ VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
 
 $(SKEL_OUT)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL)
 ifeq ($(VMLINUX_H),)
-	$(QUIET_GEN)$(BPFTOOL) btf dump file $< format c > $@
+	$(QUIET_GEN)$(BPFTOOL) btf dump file $< format c > $@ || \
+	(echo "Failure to generate vmlinux.h needed for the recommended BPF skeleton support." && \
+	echo "To disable this use the build option NO_BPF_SKEL=1." && \
+	echo "Alternatively point at a pre-generated vmlinux.h with VMLINUX_H=<path>." && \
+	false)
 else
 	$(Q)cp "$(VMLINUX_H)" $@
 endif
-- 
2.40.0.rc1.284.g88254d51c5-goog