[PATCH v4 4/4] perf build: Filter out BTF sources without a .BTF section

[Ian Rogers]

If generating vmlinux.h, make the code to generate it more tolerant by
filtering out paths to kernels that lack a .BTF section.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 tools/perf/Makefile.perf | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index 80d772cc5fcb..8f442419a895 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -197,6 +197,7 @@ FLEX    ?= flex
 BISON   ?= bison
 STRIP   = strip
 AWK     = awk
+READELF ?= readelf
 
 # include Makefile.config by default and rule out
 # non-config cases
@@ -1084,12 +1085,34 @@ $(BPFTOOL): | $(SKEL_TMP_OUT)
 	$(Q)CFLAGS= $(MAKE) -C ../bpf/bpftool \
 		OUTPUT=$(SKEL_TMP_OUT)/ bootstrap
 
-VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)				\
+# Paths to search for a kernel to generate vmlinux.h from.
+VMLINUX_BTF_ELF_PATHS ?= $(if $(O),$(O)/vmlinux)			\
 		     $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)	\
 		     ../../vmlinux					\
-		     /sys/kernel/btf/vmlinux				\
 		     /boot/vmlinux-$(shell uname -r)
-VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
+
+# Paths to BTF information.
+VMLINUX_BTF_BTF_PATHS ?= /sys/kernel/btf/vmlinux
+
+# Filter out kernels that don't exist or without a BTF section.
+VMLINUX_BTF_ELF_ABSPATHS ?= $(abspath $(wildcard $(VMLINUX_BTF_ELF_PATHS)))
+VMLINUX_BTF_PATHS ?= $(shell for file in $(VMLINUX_BTF_ELF_ABSPATHS); \
+			do \
+				if [ -f $$file ] && ($(READELF) -S "$$file" | grep -q .BTF); \
+				then \
+					echo "$$file"; \
+				fi; \
+			done) \
+			$(wildcard $(VMLINUX_BTF_BTF_PATHS))
+
+# Select the first as the source of vmlinux.h.
+VMLINUX_BTF ?= $(firstword $(VMLINUX_BTF_PATHS))
+
+ifeq ($(VMLINUX_H),)
+  ifeq ($(VMLINUX_BTF),)
+    $(error Missing bpftool input for generating vmlinux.h)
+  endif
+endif
 
 $(SKEL_OUT)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL)
 ifeq ($(VMLINUX_H),)
-- 
2.41.0.162.gfafddb0af9-goog