[PATCH] tools build feature: cleanup feature files on make clean

[Jesper Dangaard Brouer]

The system for "Auto-detecting system features" located under
tools/build/ are (currently) used by perf, libbpf and bpftool. It can
contain stalled feature detection files, which are not cleaned up by
libbpf and bpftool on make clean (side-note: perf tool is correct).

Fix this by making the users invoke the make clean target.

Some details about the changes. The libbpf Makefile already had a
clean-config target (which seems to be copy-pasted from perf), but this
target was not "connected" (a make dependency) to clean target. Choose
not to rename target as someone might be using it. Did change the output
from "CLEAN config" to "CLEAN feature-detect", to make it more clear
what happens.

This is related to the complaint and troubleshooting in link:
Link: https://lore.kernel.org/lkml/20200818122007.2d1cfe2d@carbon/

Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
---
 tools/build/Makefile |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index 8462690a039b..02c99bc95c69 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -176,7 +176,11 @@ $(OUTPUT)bpftool: $(OBJS) $(LIBBPF)
 $(OUTPUT)%.o: %.c
 	$(QUIET_CC)$(CC) $(CFLAGS) -c -MMD -o $@ $<
 
-clean: $(LIBBPF)-clean
+feature-detect-clean:
+	$(call QUIET_CLEAN, feature-detect)
+	$(Q)$(MAKE) -C $(srctree)/tools/build/feature/ clean >/dev/null
+
+clean: $(LIBBPF)-clean feature-detect-clean
 	$(call QUIET_CLEAN, bpftool)
 	$(Q)$(RM) -- $(OUTPUT)bpftool $(OUTPUT)*.o $(OUTPUT)*.d
 	$(Q)$(RM) -- $(BPFTOOL_BOOTSTRAP) $(OUTPUT)*.skel.h $(OUTPUT)vmlinux.h
diff --git a/tools/build/Makefile b/tools/build/Makefile
index 727050c40f09..722f1700d96a 100644
--- a/tools/build/Makefile
+++ b/tools/build/Makefile
@@ -38,6 +38,8 @@ clean:
 	$(call QUIET_CLEAN, fixdep)
 	$(Q)find $(if $(OUTPUT),$(OUTPUT),.) -name '*.o' -delete -o -name '\.*.cmd' -delete -o -name '\.*.d' -delete
 	$(Q)rm -f $(OUTPUT)fixdep
+	$(call QUIET_CLEAN, feature-detect)
+	$(Q)$(MAKE) -C feature/ clean >/dev/null
 
 $(OUTPUT)fixdep-in.o: FORCE
 	$(Q)$(MAKE) $(build)=fixdep
diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index bf8ed134cb8a..bbb89551468a 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -269,10 +269,10 @@ install: install_lib install_pkgconfig install_headers
 ### Cleaning rules
 
 config-clean:
-	$(call QUIET_CLEAN, config)
+	$(call QUIET_CLEAN, feature-detect)
 	$(Q)$(MAKE) -C $(srctree)/tools/build/feature/ clean >/dev/null
 
-clean:
+clean: config-clean
 	$(call QUIET_CLEAN, libbpf) $(RM) -rf $(CMD_TARGETS)		     \
 		*~ .*.d .*.cmd LIBBPF-CFLAGS $(BPF_HELPER_DEFS)		     \
 		$(SHARED_OBJDIR) $(STATIC_OBJDIR)			     \