[net-next PATCH V3 5/5] samples/bpf: like LLC also verify and allow redefining CLANG command

[Jesper Dangaard Brouer <brouer@redhat.com>]

Users are likely to manually compile both LLVM 'llc' and 'clang'
tools.  Thus, also allow redefining CLANG and verify command exist.

Makefile implementation wise, the target that verify the command have
been generalized.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
 samples/bpf/Makefile   |   25 ++++++++++++++-----------
 samples/bpf/README.rst |    6 +++---
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index dd63521832d8..157d68d6eace 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -81,9 +81,10 @@ HOSTLOADLIBES_spintest += -lelf
 HOSTLOADLIBES_map_perf_test += -lelf -lrt
 HOSTLOADLIBES_test_overhead += -lelf -lrt
 
-# Allows pointing LLC to a LLVM backend with bpf support, redefine on cmdline:
-#  make samples/bpf/ LLC=~/git/llvm/build/bin/llc
+# Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
+#  make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
 LLC ?= llc
+CLANG ?= clang
 
 # Trick to allow make to be run from this directory
 all:
@@ -93,16 +94,18 @@ clean:
 	$(MAKE) -C ../../ M=$$PWD clean
 	@rm -f *~
 
-# Verify LLVM compiler is available and bpf target is supported
-.PHONY: verify_cmd_llc verify_target_bpf
+# Verify LLVM compiler tools are available and bpf target is supported by llc
+.PHONY: verify_cmds verify_target_bpf $(CLANG) $(LLC)
 
-verify_cmd_llc:
-	@if ! (which "${LLC}" > /dev/null 2>&1); then \
-		echo "*** ERROR: Cannot find LLVM tool 'llc' (${LLC})" ;\
-		exit 1; \
-	else true; fi
+verify_cmds: $(CLANG) $(LLC)
+	@for TOOL in $^ ; do \
+		if ! (which "$${TOOL}" > /dev/null 2>&1); then \
+			echo "*** ERROR: Cannot find LLVM tool $${TOOL}" ;\
+			exit 1; \
+		else true; fi; \
+	done
 
-verify_target_bpf: verify_cmd_llc
+verify_target_bpf: verify_cmds
 	@if ! (${LLC} -march=bpf -mattr=help > /dev/null 2>&1); then \
 		echo "*** ERROR: LLVM (${LLC}) does not support 'bpf' target" ;\
 		echo "   NOTICE: LLVM version >= 3.7.1 required" ;\
@@ -115,6 +118,6 @@ $(src)/*.c: verify_target_bpf
 # But, there is no easy way to fix it, so just exclude it since it is
 # useless for BPF samples.
 $(obj)/%.o: $(src)/%.c
-	clang $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(EXTRA_CFLAGS) \
+	$(CLANG) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(EXTRA_CFLAGS) \
 		-D__KERNEL__ -D__ASM_SYSREG_H -Wno-unused-value -Wno-pointer-sign \
 		-O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf -filetype=obj -o $@
diff --git a/samples/bpf/README.rst b/samples/bpf/README.rst
index 6bbc7958c305..d653548467a5 100644
--- a/samples/bpf/README.rst
+++ b/samples/bpf/README.rst
@@ -71,8 +71,8 @@ Quick sniplet for manually compiling LLVM and clang
  $ cmake .. -DLLVM_TARGETS_TO_BUILD="BPF;X86"
  $ make -j $(getconf _NPROCESSORS_ONLN)
 
-It is also possible to point make to the newly compiled 'llc' command
-via redefining LLC on the make command line::
+It is also possible to point make to the newly compiled 'llc' or
+'clang' command via redefining LLC or CLANG on the make command line::
 
- make samples/bpf/ LLC=~/git/llvm/build/bin/llc
+ make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang