netdev - Re: [PATCH bpf-next] bpftool: make libbfd optional

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Date:   Mon, 12 Nov 2018 11:42:34 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        quentin.monnet@...ronome.com
Subject: Re: [PATCH bpf-next] bpftool: make libbfd optional

On Mon, 12 Nov 2018 10:53:28 -0800, Stanislav Fomichev wrote:
> Make it possible to build bpftool without libbfd. This excludes support for
> disassembling jit-ted code and prints an error if the user tries to use
> these features.
> 
> Tested by:
> cat > FEATURES_DUMP.bpftool <<EOF
> feature-libbfd=0
> feature-disassembler-four-args=1
> feature-reallocarray=0
> feature-libelf=1
> feature-libelf-mmap=1
> feature-bpf=1
> EOF
> FEATURES_DUMP=$PWD/FEATURES_DUMP.bpftool make
> ldd bpftool | grep libbfd
> 
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>

Would you mind spelling out the motivation?

> diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
> index 61d82020af58..ec1bc2ae3c71 100644
> --- a/tools/bpf/bpftool/main.h
> +++ b/tools/bpf/bpftool/main.h
> @@ -147,8 +147,19 @@ int prog_parse_fd(int *argc, char ***argv);
>  int map_parse_fd(int *argc, char ***argv);
>  int map_parse_fd_and_info(int *argc, char ***argv, void *info, __u32 *info_len);
>  
> +#ifdef HAVE_LIBBFD_SUPPORT
>  void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
>  		       const char *arch, const char *disassembler_options);
> +void disasm_init(void);
> +#else
> +static inline
> +void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
> +		       const char *arch, const char *disassembler_options)
> +{
> +	p_err("No libbfd support");
> +}

I think an error per instruction is a bit much, could we make sure we
error out earlier?

> +static inline void disasm_init(void) {}
> +#endif
>  void print_data_json(uint8_t *data, size_t len);
>  void print_hex_data_json(uint8_t *data, size_t len);

Otherwise LGTM.