[PATCH bpf-next v2] bpftool: make libbfd optional

[Stanislav Fomichev <sdf@google.com>]

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>
---
 tools/bpf/bpftool/Makefile     | 13 +++++++++++--
 tools/bpf/bpftool/jit_disasm.c |  8 +++++++-
 tools/bpf/bpftool/main.c       |  3 ---
 tools/bpf/bpftool/main.h       | 14 ++++++++++++++
 tools/bpf/bpftool/prog.c       |  3 +++
 5 files changed, 35 insertions(+), 6 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..b2ed5ee1af5f 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 +183,9 @@ void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
 
 	bfd_close(bfdf);
 }
+
+int disasm_init(void)
+{
+	bfd_init();
+	return 0;
+}
diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 75a3296dc0bc..5c4c1cd5a7ba 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>
@@ -399,8 +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)
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index 61d82020af58..10c6c16fae29 100644
--- a/tools/bpf/bpftool/main.h
+++ b/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);
 
diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index 5ff5544596e7..c176e1aa66fe 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/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")) {
-- 
2.19.1.930.g4563a0d9d0-goog