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Date:   Tue, 10 Mar 2020 22:44:57 +0000
From:   Quentin Monnet <quentin@...valent.com>
To:     Song Liu <songliubraving@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     kernel-team@...com, ast@...nel.org, daniel@...earbox.net,
        arnaldo.melo@...il.com, jolsa@...nel.org
Subject: Re: [PATCH bpf-next 1/2] bpftool: only build bpftool-prog-profile
 with clang >= v11

2020-03-10 11:36 UTC-0700 ~ Song Liu <songliubraving@...com>
> bpftool-prog-profile requires clang of version 11.0.0 or newer. If
> bpftool is built with older clang, show a hint of to the user.
> 
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  tools/bpf/bpftool/Makefile | 13 +++++++++++--
>  tools/bpf/bpftool/prog.c   |  2 ++
>  2 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> index 20a90d8450f8..05a37f0f76a9 100644
> --- a/tools/bpf/bpftool/Makefile
> +++ b/tools/bpf/bpftool/Makefile
> @@ -60,6 +60,15 @@ LIBS = $(LIBBPF) -lelf -lz
>  INSTALL ?= install
>  RM ?= rm -f
>  CLANG ?= clang
> +CLANG_VERS = $(shell $(CLANG) --version | head -n 1 | awk '{print $$3}')
> +CLANG_MAJ = $(shell echo $(CLANG_VERS) | cut -d '.' -f 1)

This will produce error messages on stderr if clang is not installed on
the system.

> +WITHOUT_SKELETONS = -DBPFTOOL_WITHOUT_SKELETONS
> +
> +ifeq ($(shell test $(CLANG_MAJ) -ge 11; echo $$?),0)

Not exactly what I had in mind. I thought about the feature detection
facility we have under tools/build/feature/, as is used for e.g.
detecting libbfd. It would allow to check the feature is available,
instead of tying the build to a numeric version number. But that's more
work to do, so I suppose this version can work, too...

> +	PROG_FLAGS =
> +else
> +	PROG_FLAGS = $(WITHOUT_SKELETONS)
> +endif
>  
>  FEATURE_USER = .bpftool
>  FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib
> @@ -114,7 +123,7 @@ OBJS = $(patsubst %.c,$(OUTPUT)%.o,$(SRCS)) $(OUTPUT)disasm.o
>  _OBJS = $(filter-out $(OUTPUT)prog.o,$(OBJS)) $(OUTPUT)_prog.o
>  
>  $(OUTPUT)_prog.o: prog.c
> -	$(QUIET_CC)$(COMPILE.c) -MMD -DBPFTOOL_WITHOUT_SKELETONS -o $@ $<
> +	$(QUIET_CC)$(COMPILE.c) -MMD $(WITHOUT_SKELETONS) -o $@ $<
>  
>  $(OUTPUT)_bpftool: $(_OBJS) $(LIBBPF)
>  	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(_OBJS) $(LIBS)
> @@ -126,7 +135,7 @@ profiler.skel.h: $(OUTPUT)_bpftool skeleton/profiler.bpf.o
>  	$(QUIET_GEN)$(OUTPUT)./_bpftool gen skeleton skeleton/profiler.bpf.o > $@
>  
>  $(OUTPUT)prog.o: prog.c profiler.skel.h
> -	$(QUIET_CC)$(COMPILE.c) -MMD -o $@ $<
> +	$(QUIET_CC)$(COMPILE.c) -MMD $(PROG_FLAGS) -o $@ $<

Would be nice to find a way to skip the second build if it is not needed?

>  
>  $(OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c
>  	$(QUIET_CC)$(COMPILE.c) -MMD -o $@ $<
> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> index 576ddd82bc96..5db378d5d970 100644
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -1545,6 +1545,8 @@ static int do_loadall(int argc, char **argv)
>  
>  static int do_profile(int argc, char **argv)
>  {
> +	fprintf(stdout, "bpftool prog profile command is not supported.\n"
> +		"Please recompile bpftool with clang >= 11.0.0\n");

p_err()?

>  	return 0;
>  }
>  
> 

Thanks a lot for the follow-up!
Quentin

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