[PATCH] tools/build: Use SYSTEM_BPFTOOL for system bpftool

[Tomas Glozar <tglozar@redhat.com>]

The feature test for system bpftool uses BPFTOOL as the variable to set
its path, defaulting to just "bpftool" if not set by the user.

This conflicts with selftests and a few other utilities, which expect
BPFTOOL to be set to the in-tree bpftool path by default. For example,
bpftool selftests fail to build:

$ make -C tools/testing/selftests/bpf/
make: Entering directory '/home/tglozar/dev/linux/tools/testing/selftests/bpf'

make: *** No rule to make target 'bpftool', needed by '/home/tglozar/dev/linux/tools/testing/selftests/bpf/tools/include/vmlinux.h'.  Stop.
make: Leaving directory '/home/tglozar/dev/linux/tools/testing/selftests/bpf'

Fix the problem by renaming the variable used for system bpftool from
BPFTOOL to SYSTEM_BPFTOOL, so that the new usage does not conflict with
the existing one of BPFTOOL.

Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Closes: https://lore.kernel.org/linux-kernel/5df6968a-2e5f-468e-b457-fc201535dd4c@linux.ibm.com/
Suggested-by: Quentin Monnet <qmo@qmon.net>
Fixes: 8a635c3856dd ("tools/build: Add bpftool-skeletons feature test")
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
---
 tools/build/feature/Makefile   | 2 +-
 tools/scripts/Makefile.include | 2 +-
 tools/tracing/rtla/Makefile    | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
index 4f9c1d950f5d..b8b5fb183dd4 100644
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -419,7 +419,7 @@ $(OUTPUT)test-libpfm4.bin:
 	$(BUILD) -lpfm
 
 $(OUTPUT)test-bpftool-skeletons.bin:
-	$(BPFTOOL) version | grep '^features:.*skeletons' \
+	$(SYSTEM_BPFTOOL) version | grep '^features:.*skeletons' \
 		> $(@:.bin=.make.output) 2>&1
 ###############################
 
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index 6268534309aa..5158250988ce 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -92,7 +92,7 @@ LLVM_OBJCOPY	?= llvm-objcopy
 LLVM_STRIP	?= llvm-strip
 
 # Some tools require bpftool
-BPFTOOL		?= bpftool
+SYSTEM_BPFTOOL	?= bpftool
 
 ifeq ($(CC_NO_CLANG), 1)
 EXTRA_WARNINGS += -Wstrict-aliasing=3
diff --git a/tools/tracing/rtla/Makefile b/tools/tracing/rtla/Makefile
index 4cc3017dccaa..746ccf2f5808 100644
--- a/tools/tracing/rtla/Makefile
+++ b/tools/tracing/rtla/Makefile
@@ -72,7 +72,7 @@ src/timerlat.bpf.o: src/timerlat.bpf.c
 	$(QUIET_CLANG)$(CLANG) -g -O2 -target bpf -c $(filter %.c,$^) -o $@
 
 src/timerlat.skel.h: src/timerlat.bpf.o
-	$(QUIET_GENSKEL)$(BPFTOOL) gen skeleton $< > $@
+	$(QUIET_GENSKEL)$(SYSTEM_BPFTOOL) gen skeleton $< > $@
 else
 src/timerlat.skel.h:
 	$(Q)echo '/* BPF skeleton is disabled */' > src/timerlat.skel.h
-- 
2.48.1