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

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Message-ID: <20181112195827.l5xz5qko7l6leqhp@mini-arch>
Date:   Mon, 12 Nov 2018 11:58:27 -0800
From:   Stanislav Fomichev <sdf@...ichev.me>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Stanislav Fomichev <sdf@...gle.com>, netdev@...r.kernel.org,
        ast@...nel.org, daniel@...earbox.net, quentin.monnet@...ronome.com
Subject: Re: [PATCH bpf-next] bpftool: make libbfd optional

On 11/12, Jakub Kicinski wrote:
> 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?
Ack, will do in v2 commit message. tldr - some fleet machines don't
have dev/dbg stuff installed; would like an option to have bpftool that
works everywhere for introspection.

> > 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?
I can return int from disasm_print_insn as an indication to
stop/continue. Let me know if you have better ideas, will post v2 later
today.

> > +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.
Thanks!