Subject: Re: [PATCH bpf v3] bpftool: Allow to link libbpf dynamically

From: Jiri Olsa <[email-masked]>
Date: Fri, 29 Nov 2019 09:12:51 +0100

On Thu, Nov 28, 2019 at 05:07:12PM +0100, Toke Høiland-Jørgensen wrote:

SNIP

>  ifeq ($(srctree),)
>  srctree := $(patsubst %/,%,$(dir $(CURDIR)))
> @@ -63,6 +72,19 @@ RM ?= rm -f
>  FEATURE_USER = .bpftool
>  FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib
>  FEATURE_DISPLAY = libbfd disassembler-four-args zlib
> +ifdef LIBBPF_DYNAMIC
> +  FEATURE_TESTS   += libbpf
> +  FEATURE_DISPLAY += libbpf
> +
> +  # for linking with debug library run:
> +  # make LIBBPF_DYNAMIC=1 LIBBPF_DIR=/opt/libbpf
> +  ifdef LIBBPF_DIR
> +    LIBBPF_CFLAGS  := -I$(LIBBPF_DIR)/include
> +    LIBBPF_LDFLAGS := -L$(LIBBPF_DIR)/$(libdir_relative)
> +    FEATURE_CHECK_CFLAGS-libbpf  := $(LIBBPF_CFLAGS)
> +    FEATURE_CHECK_LDFLAGS-libbpf := $(LIBBPF_LDFLAGS)
> +  endif
> +endif
>  
>  check_feat := 1
>  NON_CHECK_FEAT_TARGETS := clean uninstall doc doc-clean doc-install doc-uninstall
> @@ -88,6 +110,18 @@ ifeq ($(feature-reallocarray), 0)
>  CFLAGS += -DCOMPAT_NEED_REALLOCARRAY
>  endif
>  
> +ifdef LIBBPF_DYNAMIC
> +  ifeq ($(feature-libbpf), 1)
> +    # bpftool uses non-exported functions from libbpf, so just add the dynamic
> +    # version of libbpf and let the linker figure it out
> +    LIBS    := -lbpf $(LIBS)

nice, so linker will pick up the missing symbols and we
don't need to check on particular libbpf version then

thanks,
jirka

> +    CFLAGS  += $(LIBBPF_CFLAGS)
> +    LDFLAGS += $(LIBBPF_LDFLAGS)
> +  else
> +    dummy := $(error Error: No libbpf devel library found, please install libbpf-devel or libbpf-dev.)
> +  endif
> +endif
> +
>  include $(wildcard $(OUTPUT)*.d)
>  
>  all: $(OUTPUT)bpftool
> -- 
> 2.24.0
>