Re: [PATCH] samples/bpf: Add BTF build flags to Makefile

[Jakub Kicinski]

On Thu, 26 Jul 2018 01:30:39 +0900, Taeung Song wrote:
> To smoothly test BTF supported binary on samples/bpf,
> let samples/bpf/Makefile probe llc, pahole and
> llvm-objcopy for BPF support and use them
> like tools/testing/selftests/bpf/Makefile
> changed from the commit c0fa1b6c3efc ("bpf: btf:
>  Add BTF tests")
> 
> Cc: Martin KaFai Lau <kafai@xxxxxx>
> Signed-off-by: Taeung Song <treeze.taeung@xxxxxxxxx>
> ---
>  samples/bpf/Makefile | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> index 1303af10e54d..e079266360a3 100644
> --- a/samples/bpf/Makefile
> +++ b/samples/bpf/Makefile
> @@ -191,6 +191,8 @@ HOSTLOADLIBES_xdpsock		+= -pthread
>  #  make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
>  LLC ?= llc
>  CLANG ?= clang
> +LLVM_OBJCOPY ?= llvm-objcopy
> +BTF_PAHOLE ?= pahole
>  
>  # Detect that we're cross compiling and use the cross compiler
>  ifdef CROSS_COMPILE
> @@ -198,6 +200,20 @@ HOSTCC = $(CROSS_COMPILE)gcc
>  CLANG_ARCH_ARGS = -target $(ARCH)
>  endif
>  
> +BTF_LLC_PROBE := $(shell $(LLC) -march=bpf -mattr=help 2>&1 | grep dwarfris)
> +BTF_PAHOLE_PROBE := $(shell $(BTF_PAHOLE) --help 2>&1 | grep BTF)
> +BTF_OBJCOPY_PROBE := $(shell $(LLVM_OBJCOPY) --help 2>&1 | grep -i 'usage.*llvm')
> +
> +ifneq ($(BTF_LLC_PROBE),)
> +ifneq ($(BTF_PAHOLE_PROBE),)
> +ifneq ($(BTF_OBJCOPY_PROBE),)

Nice patch!  FWIW you could consider using $(and ...) here:

ifneq ($(and $(BTF_LLC_PROBE),$(BTF_PAHOLE_PROBE),$(BTF_OBJCOPY_PROBE)),)

https://www.gnu.org/software/make/manual/html_node/Conditional-Functions.html#Conditional-Functions

Not sure it's worth a respin..

> +	EXTRA_CFLAGS += -g
> +	LLC_FLAGS += -mattr=dwarfris
> +	DWARF2BTF = y
> +endif
> +endif
> +endif
> +
>  # Trick to allow make to be run from this directory
>  all:
>  	$(MAKE) -C ../../ $(CURDIR)/ BPF_SAMPLES_PATH=$(CURDIR)
> @@ -256,4 +272,7 @@ $(obj)/%.o: $(src)/%.c
>  		-Wno-gnu-variable-sized-type-not-at-end \
>  		-Wno-address-of-packed-member -Wno-tautological-compare \
>  		-Wno-unknown-warning-option $(CLANG_ARCH_ARGS) \
> -		-O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf -filetype=obj -o $@
> +		-O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
> +ifeq ($(DWARF2BTF),y)
> +	$(BTF_PAHOLE) -J $@
> +endif