bpftool: make libbfd optional

Make it possible to build bpftool without libbfd. libbfd and libopcodes are
typically provided in dev/dbg packages (binutils-dev in debian) which we
usually don't have installed on the fleet machines and we'd like a way to have
bpftool version that works without installing any additional packages.
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>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

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 +183,9 @@ void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
 
 	bfd_close(bfdf);
 }
+
+int disasm_init(void)
+{
+	bfd_init();
+	return 0;
+}

tools/bpf/bpftool/main.c

@@ -31,7 +31,6 @@
  * SOFTWARE.
  */
 
-#include <bfd.h>
 #include <ctype.h>
 #include <errno.h>
 #include <getopt.h>
@@ -399,8 +398,6 @@ int main(int argc, char **argv)
 	if (argc < 0)
 		usage();
 
-	bfd_init();
-
 	ret = cmd_select(cmds, argc, argv, do_help);
 
 	if (json_output)

tools/bpf/bpftool/main.h

@@ -147,8 +147,22 @@ 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);
+int 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)
+{
+}
+static inline int disasm_init(void)
+{
+	p_err("No libbfd support");
+	return -1;
+}
+#endif
 void print_data_json(uint8_t *data, size_t len);
 void print_hex_data_json(uint8_t *data, size_t len);
 

tools/bpf/bpftool/prog.c

@@ -467,6 +467,9 @@ static int do_dump(int argc, char **argv)
 	int fd;
 
 	if (is_prefix(*argv, "jited")) {
+		if (disasm_init())
+			return -1;
+
 		member_len = &info.jited_prog_len;
 		member_ptr = &info.jited_prog_insns;
 	} else if (is_prefix(*argv, "xlated")) {