tools build: Add feature detection for LLVM

Check if basic LLVM compiling environment is ready.

Use llvm-config to detect include and library directories. Avoid using
'llvm-config --cxxflags' because its result contain some unwanted flags
like --sysroot (if LLVM is built by yocto).

Use '?=' to set LLVM_CONFIG, so explicitly passing LLVM_CONFIG to make
would override it.

Use 'llvm-config --libs BPF' to check if BPF backend is compiled in.
Since now BPF bytecode is the only required backend, no need to waste
time linking llvm and clang if BPF backend is missing. This also
introduce an implicit requirement that LLVM should be new enough.  Old
LLVM doesn't support BPF backend.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Joe Stringer <joe@ovn.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/20161126070354.141764-8-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
index 8f668bce8996d772140c0a2b53e23af614d60b3d..c09de59affc972d8afbf8e4351967d75690641ec 100644 (file)
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -55,6 +55,7 @@ FILES := $(addprefix $(OUTPUT),$(FILES))
 CC := $(CROSS_COMPILE)gcc -MD
 CXX := $(CROSS_COMPILE)g++ -MD
 PKG_CONFIG := $(CROSS_COMPILE)pkg-config
+LLVM_CONFIG ?= llvm-config
 
 all: $(FILES)
 
@@ -229,6 +230,13 @@ $(OUTPUT)test-cxx.bin:
 $(OUTPUT)test-jvmti.bin:
        $(BUILD)
 
+$(OUTPUT)test-llvm.bin:
+       $(BUILDXX) -std=gnu++11                                         \
+               -I$(shell $(LLVM_CONFIG) --includedir)          \
+               -L$(shell $(LLVM_CONFIG) --libdir)              \
+               $(shell $(LLVM_CONFIG) --libs Core BPF)         \
+               $(shell $(LLVM_CONFIG) --system-libs)
+
 -include $(OUTPUT)*.d
 
 ###############################

diff --git a/tools/build/feature/test-llvm.cpp b/tools/build/feature/test-llvm.cpp
new file mode 100644 (file)
index 0000000..d8d2cee
--- /dev/null
+++ b/tools/build/feature/test-llvm.cpp
@@ -0,0 +1,8 @@
+#include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/raw_ostream.h"
+int main()
+{
+       llvm::errs() << "Hello World!\n";
+       llvm::llvm_shutdown();
+       return 0;
+}