[PATCH bpf-next] bpftool: make libbfd optional

[PATCH bpf-next] bpftool: make libbfd optional

[Stanislav Fomichev]

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@google.com>
---
 tools/bpf/bpftool/Makefile     | 13 +++++++++++--
 tools/bpf/bpftool/jit_disasm.c |  7 ++++++-
 tools/bpf/bpftool/main.c       |  3 +--
 tools/bpf/bpftool/main.h       | 11 +++++++++++
 4 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index dac7eff4c7e5..1bea6b979082 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -53,7 +53,7 @@ ifneq ($(EXTRA_LDFLAGS),)
 LDFLAGS += $(EXTRA_LDFLAGS)
 endif
 
-LIBS = -lelf -lbfd -lopcodes $(LIBBPF)
+LIBS = -lelf $(LIBBPF)
 
 INSTALL ?= install
 RM ?= rm -f
@@ -90,7 +90,16 @@ include $(wildcard $(OUTPUT)*.d)
 
 all: $(OUTPUT)bpftool
 
-SRCS = $(wildcard *.c)
+BFD_SRCS = jit_disasm.c
+
+SRCS = $(filter-out $(BFD_SRCS),$(wildcard *.c))
+
+ifeq ($(feature-libbfd),1)
+CFLAGS += -DHAVE_LIBBFD_SUPPORT
+SRCS += $(BFD_SRCS)
+LIBS += -lbfd -lopcodes
+endif
+
 OBJS = $(patsubst %.c,$(OUTPUT)%.o,$(SRCS)) $(OUTPUT)disasm.o
 
 $(OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c
diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c
index c75ffd9ce2bb..6176bfe66f22 100644
--- a/tools/bpf/bpftool/jit_disasm.c
+++ b/tools/bpf/bpftool/jit_disasm.c
@@ -109,7 +109,7 @@ void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
 		if (inf) {
 			bfdf->arch_info = inf;
 		} else {
-			p_err("No libfd support for %s", arch);
+			p_err("No libbfd support for %s", arch);
 			return;
 		}
 	}
@@ -183,3 +183,8 @@ void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
 
 	bfd_close(bfdf);
 }
+
+void disasm_init(void)
+{
+	bfd_init();
+}
diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 75a3296dc0bc..51aa71069b14 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -31,7 +31,6 @@
  * SOFTWARE.
  */
 
-#include <bfd.h>
 #include <ctype.h>
 #include <errno.h>
 #include <getopt.h>
@@ -399,7 +398,7 @@ int main(int argc, char **argv)
 	if (argc < 0)
 		usage();
 
-	bfd_init();
+	disasm_init();
 
 	ret = cmd_select(cmds, argc, argv, do_help);
 
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");
+}
+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);
 
-- 
2.19.1.930.g4563a0d9d0-goog

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

[Jakub Kicinski]

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@google.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.

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

[Stanislav Fomichev]

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@google.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!

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

[Jakub Kicinski]

On Mon, 12 Nov 2018 11:58:27 -0800, Stanislav Fomichev wrote:
> On 11/12, Jakub Kicinski wrote:
> > On Mon, 12 Nov 2018 10:53:28 -0800, Stanislav Fomichev wrote:  
> > > 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.

Why not simply:

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index 5302ee282409..44edf6705ad2 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -466,6 +466,10 @@ static int do_dump(int argc, char **argv)
        int fd;
 
        if (is_prefix(*argv, "jited")) {
+#ifndef HAVE_LIBBFD_SUPPORT
+               p_err("No libbfd support");
+               return -1;
+#endif
                member_len = &info.jited_prog_len;
                member_ptr = &info.jited_prog_insns;
        } else if (is_prefix(*argv, "xlated")) {

Perhaps wrapped into some helper in the header to avoid the yuckiness.

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

[Stanislav Fomichev]

On 11/12, Jakub Kicinski wrote:
> On Mon, 12 Nov 2018 11:58:27 -0800, Stanislav Fomichev wrote:
> > On 11/12, Jakub Kicinski wrote:
> > > On Mon, 12 Nov 2018 10:53:28 -0800, Stanislav Fomichev wrote:  
> > > > 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.
> 
> Why not simply:
Makes sense. I think I can actually repurpose disasm_init for that (the
function I added to wrap bfd_init, I think I can move the callsite here
without any problems).

> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> index 5302ee282409..44edf6705ad2 100644
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -466,6 +466,10 @@ static int do_dump(int argc, char **argv)
>         int fd;
>  
>         if (is_prefix(*argv, "jited")) {
> +#ifndef HAVE_LIBBFD_SUPPORT
> +               p_err("No libbfd support");
> +               return -1;
> +#endif
>                 member_len = &info.jited_prog_len;
>                 member_ptr = &info.jited_prog_insns;
>         } else if (is_prefix(*argv, "xlated")) {
> 
> Perhaps wrapped into some helper in the header to avoid the yuckiness.