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[PATCHv3 perf/core 5/7] samples/bpf: Switch over to libbpf

Started byJoe Stringer <joe@ovn.org>
First post2016-12-09 03:50 +0100
Last post2016-12-09 19:10 +0100
Articles 4 — 2 participants

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  [PATCHv3 perf/core 5/7] samples/bpf: Switch over to libbpf Joe Stringer <joe@ovn.org> - 2016-12-09 03:50 +0100
    Re: [PATCHv3 perf/core 5/7] samples/bpf: Switch over to libbpf "Wangnan (F)" <wangnan0@huawei.com> - 2016-12-09 06:10 +0100
      Re: [PATCHv3 perf/core 5/7] samples/bpf: Switch over to libbpf "Wangnan (F)" <wangnan0@huawei.com> - 2016-12-09 06:20 +0100
        Re: [PATCHv3 perf/core 5/7] samples/bpf: Switch over to libbpf Joe Stringer <joe@ovn.org> - 2016-12-09 19:10 +0100

#1539032 — [PATCHv3 perf/core 5/7] samples/bpf: Switch over to libbpf

FromJoe Stringer <joe@ovn.org>
Date2016-12-09 03:50 +0100
Subject[PATCHv3 perf/core 5/7] samples/bpf: Switch over to libbpf
Message-ID<sMjq2-5Sr-41@gated-at.bofh.it>
Now that libbpf under tools/lib/bpf/* is synced with the version from
samples/bpf, we can get rid most of the libbpf library here.

Signed-off-by: Joe Stringer <joe@ovn.org>
---
v3: First post.
---
 samples/bpf/Makefile   |  60 +++++++++++++-------------
 samples/bpf/README.rst |   4 +-
 samples/bpf/libbpf.c   | 111 -------------------------------------------------
 samples/bpf/libbpf.h   |  19 +--------
 tools/lib/bpf/Makefile |   2 +
 5 files changed, 38 insertions(+), 158 deletions(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 72c58675973e..c8f7ed37b2de 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -29,35 +29,38 @@ hostprogs-y += trace_event
 hostprogs-y += sampleip
 hostprogs-y += tc_l2_redirect
 
-test_verifier-objs := test_verifier.o libbpf.o
-test_maps-objs := test_maps.o libbpf.o
-sock_example-objs := sock_example.o libbpf.o
-fds_example-objs := bpf_load.o libbpf.o fds_example.o
-sockex1-objs := bpf_load.o libbpf.o sockex1_user.o
-sockex2-objs := bpf_load.o libbpf.o sockex2_user.o
-sockex3-objs := bpf_load.o libbpf.o sockex3_user.o
-tracex1-objs := bpf_load.o libbpf.o tracex1_user.o
-tracex2-objs := bpf_load.o libbpf.o tracex2_user.o
-tracex3-objs := bpf_load.o libbpf.o tracex3_user.o
-tracex4-objs := bpf_load.o libbpf.o tracex4_user.o
-tracex5-objs := bpf_load.o libbpf.o tracex5_user.o
-tracex6-objs := bpf_load.o libbpf.o tracex6_user.o
-test_probe_write_user-objs := bpf_load.o libbpf.o test_probe_write_user_user.o
-trace_output-objs := bpf_load.o libbpf.o trace_output_user.o
-lathist-objs := bpf_load.o libbpf.o lathist_user.o
-offwaketime-objs := bpf_load.o libbpf.o offwaketime_user.o
-spintest-objs := bpf_load.o libbpf.o spintest_user.o
-map_perf_test-objs := bpf_load.o libbpf.o map_perf_test_user.o
-test_overhead-objs := bpf_load.o libbpf.o test_overhead_user.o
-test_cgrp2_array_pin-objs := libbpf.o test_cgrp2_array_pin.o
-xdp1-objs := bpf_load.o libbpf.o xdp1_user.o
+# Libbpf dependencies
+LIBBPF := libbpf.o ../../tools/lib/bpf/bpf.o
+
+test_verifier-objs := test_verifier.o $(LIBBPF)
+test_maps-objs := test_maps.o $(LIBBPF)
+sock_example-objs := sock_example.o $(LIBBPF)
+fds_example-objs := bpf_load.o $(LIBBPF) fds_example.o
+sockex1-objs := bpf_load.o $(LIBBPF) sockex1_user.o
+sockex2-objs := bpf_load.o $(LIBBPF) sockex2_user.o
+sockex3-objs := bpf_load.o $(LIBBPF) sockex3_user.o
+tracex1-objs := bpf_load.o $(LIBBPF) tracex1_user.o
+tracex2-objs := bpf_load.o $(LIBBPF) tracex2_user.o
+tracex3-objs := bpf_load.o $(LIBBPF) tracex3_user.o
+tracex4-objs := bpf_load.o $(LIBBPF) tracex4_user.o
+tracex5-objs := bpf_load.o $(LIBBPF) tracex5_user.o
+tracex6-objs := bpf_load.o $(LIBBPF) tracex6_user.o
+test_probe_write_user-objs := bpf_load.o $(LIBBPF) test_probe_write_user_user.o
+trace_output-objs := bpf_load.o $(LIBBPF) trace_output_user.o
+lathist-objs := bpf_load.o $(LIBBPF) lathist_user.o
+offwaketime-objs := bpf_load.o $(LIBBPF) offwaketime_user.o
+spintest-objs := bpf_load.o $(LIBBPF) spintest_user.o
+map_perf_test-objs := bpf_load.o $(LIBBPF) map_perf_test_user.o
+test_overhead-objs := bpf_load.o $(LIBBPF) test_overhead_user.o
+test_cgrp2_array_pin-objs := $(LIBBPF) test_cgrp2_array_pin.o
+xdp1-objs := bpf_load.o $(LIBBPF) xdp1_user.o
 # reuse xdp1 source intentionally
-xdp2-objs := bpf_load.o libbpf.o xdp1_user.o
-test_current_task_under_cgroup-objs := bpf_load.o libbpf.o \
+xdp2-objs := bpf_load.o $(LIBBPF) xdp1_user.o
+test_current_task_under_cgroup-objs := bpf_load.o $(LIBBPF) \
 				       test_current_task_under_cgroup_user.o
-trace_event-objs := bpf_load.o libbpf.o trace_event_user.o
-sampleip-objs := bpf_load.o libbpf.o sampleip_user.o
-tc_l2_redirect-objs := bpf_load.o libbpf.o tc_l2_redirect_user.o
+trace_event-objs := bpf_load.o $(LIBBPF) trace_event_user.o
+sampleip-objs := bpf_load.o $(LIBBPF) sampleip_user.o
+tc_l2_redirect-objs := bpf_load.o $(LIBBPF) tc_l2_redirect_user.o
 
 # Tell kbuild to always build the programs
 always := $(hostprogs-y)
@@ -89,7 +92,7 @@ always += test_current_task_under_cgroup_kern.o
 always += trace_event_kern.o
 always += sampleip_kern.o
 
-HOSTCFLAGS += -I$(objtree)/usr/include
+HOSTCFLAGS += -I$(objtree)/usr/include -I$(objtree)/tools/lib/
 
 HOSTCFLAGS_bpf_load.o += -I$(objtree)/usr/include -Wno-unused-variable
 HOSTLOADLIBES_fds_example += -lelf
@@ -123,6 +126,7 @@ CLANG ?= clang
 
 # Trick to allow make to be run from this directory
 all:
+	$(MAKE) -C ../../ tools/lib/bpf/
 	$(MAKE) -C ../../ $$PWD/
 
 clean:
diff --git a/samples/bpf/README.rst b/samples/bpf/README.rst
index a43eae3f0551..79f9a58f1872 100644
--- a/samples/bpf/README.rst
+++ b/samples/bpf/README.rst
@@ -1,8 +1,8 @@
 eBPF sample programs
 ====================
 
-This directory contains a mini eBPF library, test stubs, verifier
-test-suite and examples for using eBPF.
+This directory contains a test stubs, verifier test-suite and examples
+for using eBPF. The examples use libbpf from tools/lib/bpf.
 
 Build dependencies
 ==================
diff --git a/samples/bpf/libbpf.c b/samples/bpf/libbpf.c
index e5c5a69996fc..d9af876b4a2c 100644
--- a/samples/bpf/libbpf.c
+++ b/samples/bpf/libbpf.c
@@ -4,8 +4,6 @@
 #include <linux/unistd.h>
 #include <unistd.h>
 #include <string.h>
-#include <linux/netlink.h>
-#include <linux/bpf.h>
 #include <errno.h>
 #include <net/ethernet.h>
 #include <net/if.h>
@@ -13,115 +11,6 @@
 #include <arpa/inet.h>
 #include "libbpf.h"
 
-static __u64 ptr_to_u64(void *ptr)
-{
-	return (__u64) (unsigned long) ptr;
-}
-
-int bpf_create_map(enum bpf_map_type map_type, int key_size, int value_size,
-		   int max_entries, int map_flags)
-{
-	union bpf_attr attr = {
-		.map_type = map_type,
-		.key_size = key_size,
-		.value_size = value_size,
-		.max_entries = max_entries,
-		.map_flags = map_flags,
-	};
-
-	return syscall(__NR_bpf, BPF_MAP_CREATE, &attr, sizeof(attr));
-}
-
-int bpf_map_update_elem(int fd, void *key, void *value, unsigned long long flags)
-{
-	union bpf_attr attr = {
-		.map_fd = fd,
-		.key = ptr_to_u64(key),
-		.value = ptr_to_u64(value),
-		.flags = flags,
-	};
-
-	return syscall(__NR_bpf, BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr));
-}
-
-int bpf_map_lookup_elem(int fd, void *key, void *value)
-{
-	union bpf_attr attr = {
-		.map_fd = fd,
-		.key = ptr_to_u64(key),
-		.value = ptr_to_u64(value),
-	};
-
-	return syscall(__NR_bpf, BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr));
-}
-
-int bpf_map_delete_elem(int fd, void *key)
-{
-	union bpf_attr attr = {
-		.map_fd = fd,
-		.key = ptr_to_u64(key),
-	};
-
-	return syscall(__NR_bpf, BPF_MAP_DELETE_ELEM, &attr, sizeof(attr));
-}
-
-int bpf_map_get_next_key(int fd, void *key, void *next_key)
-{
-	union bpf_attr attr = {
-		.map_fd = fd,
-		.key = ptr_to_u64(key),
-		.next_key = ptr_to_u64(next_key),
-	};
-
-	return syscall(__NR_bpf, BPF_MAP_GET_NEXT_KEY, &attr, sizeof(attr));
-}
-
-#define ROUND_UP(x, n) (((x) + (n) - 1u) & ~((n) - 1u))
-
-int bpf_load_program(enum bpf_prog_type prog_type,
-		     const struct bpf_insn *insns, int prog_len,
-		     const char *license, int kern_version,
-		     char *log_buf, size_t log_buf_sz)
-{
-	union bpf_attr attr = {
-		.prog_type = prog_type,
-		.insns = ptr_to_u64((void *) insns),
-		.insn_cnt = prog_len / sizeof(struct bpf_insn),
-		.license = ptr_to_u64((void *) license),
-		.log_buf = ptr_to_u64(log_buf),
-		.log_size = log_buf_sz,
-		.log_level = 1,
-	};
-
-	/* assign one field outside of struct init to make sure any
-	 * padding is zero initialized
-	 */
-	attr.kern_version = kern_version;
-
-	log_buf[0] = 0;
-
-	return syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr));
-}
-
-int bpf_obj_pin(int fd, const char *pathname)
-{
-	union bpf_attr attr = {
-		.pathname	= ptr_to_u64((void *)pathname),
-		.bpf_fd		= fd,
-	};
-
-	return syscall(__NR_bpf, BPF_OBJ_PIN, &attr, sizeof(attr));
-}
-
-int bpf_obj_get(const char *pathname)
-{
-	union bpf_attr attr = {
-		.pathname	= ptr_to_u64((void *)pathname),
-	};
-
-	return syscall(__NR_bpf, BPF_OBJ_GET, &attr, sizeof(attr));
-}
-
 int open_raw_sock(const char *name)
 {
 	struct sockaddr_ll sll;
diff --git a/samples/bpf/libbpf.h b/samples/bpf/libbpf.h
index 1325152be4cd..cc815624aacf 100644
--- a/samples/bpf/libbpf.h
+++ b/samples/bpf/libbpf.h
@@ -2,24 +2,9 @@
 #ifndef __LIBBPF_H
 #define __LIBBPF_H
 
-struct bpf_insn;
-
-int bpf_create_map(enum bpf_map_type map_type, int key_size, int value_size,
-		   int max_entries, int map_flags);
-int bpf_map_update_elem(int fd, void *key, void *value, unsigned long long flags);
-int bpf_map_lookup_elem(int fd, void *key, void *value);
-int bpf_map_delete_elem(int fd, void *key);
-int bpf_map_get_next_key(int fd, void *key, void *next_key);
-
-int bpf_load_program(enum bpf_prog_type prog_type,
-		     const struct bpf_insn *insns, int insn_len,
-		     const char *license, int kern_version,
-		     char *log_buf, size_t log_buf_sz);
+#include <bpf/bpf.h>
 
-int bpf_obj_pin(int fd, const char *pathname);
-int bpf_obj_get(const char *pathname);
-
-#define BPF_LOG_BUF_SIZE 65536
+struct bpf_insn;
 
 /* ALU ops on registers, bpf_add|sub|...: dst_reg += src_reg */
 
diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 62d89d50fcbd..616bd55f3be8 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -149,6 +149,8 @@ CMD_TARGETS = $(LIB_FILE)
 
 TARGETS = $(CMD_TARGETS)
 
+libbpf: all
+
 all: fixdep $(VERSION_FILES) all_cmd
 
 all_cmd: $(CMD_TARGETS)
-- 
2.10.2

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#1539076

From"Wangnan (F)" <wangnan0@huawei.com>
Date2016-12-09 06:10 +0100
Message-ID<sMlBw-7ym-7@gated-at.bofh.it>
In reply to#1539032

On 2016/12/9 10:46, Joe Stringer wrote:
> Now that libbpf under tools/lib/bpf/* is synced with the version from
> samples/bpf, we can get rid most of the libbpf library here.
>
> Signed-off-by: Joe Stringer <joe@ovn.org>
> ---
> v3: First post.
> ---
>   samples/bpf/Makefile   |  60 +++++++++++++-------------
>   samples/bpf/README.rst |   4 +-
>   samples/bpf/libbpf.c   | 111 -------------------------------------------------
>   samples/bpf/libbpf.h   |  19 +--------
>   tools/lib/bpf/Makefile |   2 +
>   5 files changed, 38 insertions(+), 158 deletions(-)
>
> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> index 72c58675973e..c8f7ed37b2de 100644
> --- a/samples/bpf/Makefile
> +++ b/samples/bpf/Makefile
> @@ -29,35 +29,38 @@ hostprogs-y += trace_event
>   hostprogs-y += sampleip
>   hostprogs-y += tc_l2_redirect
>   
> -test_verifier-objs := test_verifier.o libbpf.o
> -test_maps-objs := test_maps.o libbpf.o
> -sock_example-objs := sock_example.o libbpf.o
> -fds_example-objs := bpf_load.o libbpf.o fds_example.o
> -sockex1-objs := bpf_load.o libbpf.o sockex1_user.o
> -sockex2-objs := bpf_load.o libbpf.o sockex2_user.o
> -sockex3-objs := bpf_load.o libbpf.o sockex3_user.o
> -tracex1-objs := bpf_load.o libbpf.o tracex1_user.o
> -tracex2-objs := bpf_load.o libbpf.o tracex2_user.o
> -tracex3-objs := bpf_load.o libbpf.o tracex3_user.o
> -tracex4-objs := bpf_load.o libbpf.o tracex4_user.o
> -tracex5-objs := bpf_load.o libbpf.o tracex5_user.o
> -tracex6-objs := bpf_load.o libbpf.o tracex6_user.o
> -test_probe_write_user-objs := bpf_load.o libbpf.o test_probe_write_user_user.o
> -trace_output-objs := bpf_load.o libbpf.o trace_output_user.o
> -lathist-objs := bpf_load.o libbpf.o lathist_user.o
> -offwaketime-objs := bpf_load.o libbpf.o offwaketime_user.o
> -spintest-objs := bpf_load.o libbpf.o spintest_user.o
> -map_perf_test-objs := bpf_load.o libbpf.o map_perf_test_user.o
> -test_overhead-objs := bpf_load.o libbpf.o test_overhead_user.o
> -test_cgrp2_array_pin-objs := libbpf.o test_cgrp2_array_pin.o
> -xdp1-objs := bpf_load.o libbpf.o xdp1_user.o
> +# Libbpf dependencies
> +LIBBPF := libbpf.o ../../tools/lib/bpf/bpf.o
> +
> +test_verifier-objs := test_verifier.o $(LIBBPF)
> +test_maps-objs := test_maps.o $(LIBBPF)
> +sock_example-objs := sock_example.o $(LIBBPF)
> +fds_example-objs := bpf_load.o $(LIBBPF) fds_example.o
> +sockex1-objs := bpf_load.o $(LIBBPF) sockex1_user.o
> +sockex2-objs := bpf_load.o $(LIBBPF) sockex2_user.o
> +sockex3-objs := bpf_load.o $(LIBBPF) sockex3_user.o
> +tracex1-objs := bpf_load.o $(LIBBPF) tracex1_user.o
> +tracex2-objs := bpf_load.o $(LIBBPF) tracex2_user.o
> +tracex3-objs := bpf_load.o $(LIBBPF) tracex3_user.o
> +tracex4-objs := bpf_load.o $(LIBBPF) tracex4_user.o
> +tracex5-objs := bpf_load.o $(LIBBPF) tracex5_user.o
> +tracex6-objs := bpf_load.o $(LIBBPF) tracex6_user.o
> +test_probe_write_user-objs := bpf_load.o $(LIBBPF) test_probe_write_user_user.o
> +trace_output-objs := bpf_load.o $(LIBBPF) trace_output_user.o
> +lathist-objs := bpf_load.o $(LIBBPF) lathist_user.o
> +offwaketime-objs := bpf_load.o $(LIBBPF) offwaketime_user.o
> +spintest-objs := bpf_load.o $(LIBBPF) spintest_user.o
> +map_perf_test-objs := bpf_load.o $(LIBBPF) map_perf_test_user.o
> +test_overhead-objs := bpf_load.o $(LIBBPF) test_overhead_user.o
> +test_cgrp2_array_pin-objs := $(LIBBPF) test_cgrp2_array_pin.o
> +xdp1-objs := bpf_load.o $(LIBBPF) xdp1_user.o
>   # reuse xdp1 source intentionally
> -xdp2-objs := bpf_load.o libbpf.o xdp1_user.o
> -test_current_task_under_cgroup-objs := bpf_load.o libbpf.o \
> +xdp2-objs := bpf_load.o $(LIBBPF) xdp1_user.o
> +test_current_task_under_cgroup-objs := bpf_load.o $(LIBBPF) \
>   				       test_current_task_under_cgroup_user.o
> -trace_event-objs := bpf_load.o libbpf.o trace_event_user.o
> -sampleip-objs := bpf_load.o libbpf.o sampleip_user.o
> -tc_l2_redirect-objs := bpf_load.o libbpf.o tc_l2_redirect_user.o
> +trace_event-objs := bpf_load.o $(LIBBPF) trace_event_user.o
> +sampleip-objs := bpf_load.o $(LIBBPF) sampleip_user.o
> +tc_l2_redirect-objs := bpf_load.o $(LIBBPF) tc_l2_redirect_user.o
>   
>   # Tell kbuild to always build the programs
>   always := $(hostprogs-y)
> @@ -89,7 +92,7 @@ always += test_current_task_under_cgroup_kern.o
>   always += trace_event_kern.o
>   always += sampleip_kern.o
>   
> -HOSTCFLAGS += -I$(objtree)/usr/include
> +HOSTCFLAGS += -I$(objtree)/usr/include -I$(objtree)/tools/lib/
>   

Should use srctree like this:

+HOSTCFLAGS += -I$(objtree)/usr/include -I$(srctree)/tools/lib/

Or you will see following failure when doing off-tree build:

  $ mkdir buildkernel
  $ cd buildkernel
  $ make -C ../ O=`pwd` menuconfig
  $ make -j64
  $ make samples/bpf/
   CHK     include/config/kernel.release
   Using .. as source for kernel
   GEN     ./Makefile
   CHK     include/generated/uapi/linux/version.h
   CHK     include/generated/utsrelease.h
   CHK     include/generated/bounds.h
   CHK     include/generated/timeconst.h
   CHK     include/generated/asm-offsets.h
   CALL    ../scripts/checksyscalls.sh
   HOSTCC  samples/bpf/test_verifier.o
  In file included from ../samples/bpf/test_verifier.c:20:0:
  ../samples/bpf/libbpf.h:5:21: fatal error: bpf/bpf.h: No such file or 
directory
   #include <bpf/bpf.h>
                       ^
  compilation terminated.
  make[3]: *** [samples/bpf/test_verifier.o] Error 1
  make[2]: *** [samples/bpf/] Error 2
  make[1]: *** [sub-make] Error 2
  make: *** [__sub-make] Error 2

>   HOSTCFLAGS_bpf_load.o += -I$(objtree)/usr/include -Wno-unused-variable
>   HOSTLOADLIBES_fds_example += -lelf
> @@ -123,6 +126,7 @@ CLANG ?= clang
>   
>   # Trick to allow make to be run from this directory
>   all:
> +	$(MAKE) -C ../../ tools/lib/bpf/
>   	$(MAKE) -C ../../ $$PWD/
>   
>   clean:

[SNIP]

>   
> diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
> index 62d89d50fcbd..616bd55f3be8 100644
> --- a/tools/lib/bpf/Makefile
> +++ b/tools/lib/bpf/Makefile
> @@ -149,6 +149,8 @@ CMD_TARGETS = $(LIB_FILE)
>   
>   TARGETS = $(CMD_TARGETS)
>   
> +libbpf: all
> +

Why we need this? I tested this patch without it and it seems to work, and
this line causes an extra error:
  $ pwd
  /home/wn/kernel/tools/lib/bpf
  $ make libbpf
  ...
  gcc -g -Wall -DHAVE_LIBELF_MMAP_SUPPORT -DHAVE_ELF_GETPHDRNUM_SUPPORT 
-Wbad-function-cast -Wdeclaration-after-statement -Wformat-security 
-Wformat-y2k -Winit-self -Wmissing-declarations -Wmissing-prototypes 
-Wnested-externs -Wno-system-headers -Wold-style-definition -Wpacked 
-Wredundant-decls -Wshadow -Wstrict-aliasing=3 -Wstrict-prototypes 
-Wswitch-default -Wswitch-enum -Wundef -Wwrite-strings -Wformat -Werror 
-Wall -fPIC -I. -I/home/wn/kernel-hydrogen/tools/include 
-I/home/wn/kernel-hydrogen/tools/arch/x86/include/uapi 
-I/home/wn/kernel-hydrogen/tools/include/uapi    libbpf.c all   -o libbpf
  gcc: error: all: No such file or directory
  make: *** [libbpf] Error 1

Thank you.

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#1539090

From"Wangnan (F)" <wangnan0@huawei.com>
Date2016-12-09 06:20 +0100
Message-ID<sMlLc-7BJ-23@gated-at.bofh.it>
In reply to#1539076

On 2016/12/9 13:04, Wangnan (F) wrote:
>
>
> On 2016/12/9 10:46, Joe Stringer wrote:
>
> [SNIP]
>
>>   diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
>> index 62d89d50fcbd..616bd55f3be8 100644
>> --- a/tools/lib/bpf/Makefile
>> +++ b/tools/lib/bpf/Makefile
>> @@ -149,6 +149,8 @@ CMD_TARGETS = $(LIB_FILE)
>>     TARGETS = $(CMD_TARGETS)
>>   +libbpf: all
>> +
>
> Why we need this? I tested this patch without it and it seems to work, 
> and
> this line causes an extra error:
>  $ pwd
>  /home/wn/kernel/tools/lib/bpf
>  $ make libbpf
>  ...
>  gcc -g -Wall -DHAVE_LIBELF_MMAP_SUPPORT -DHAVE_ELF_GETPHDRNUM_SUPPORT 
> -Wbad-function-cast -Wdeclaration-after-statement -Wformat-security 
> -Wformat-y2k -Winit-self -Wmissing-declarations -Wmissing-prototypes 
> -Wnested-externs -Wno-system-headers -Wold-style-definition -Wpacked 
> -Wredundant-decls -Wshadow -Wstrict-aliasing=3 -Wstrict-prototypes 
> -Wswitch-default -Wswitch-enum -Wundef -Wwrite-strings -Wformat 
> -Werror -Wall -fPIC -I. -I/home/wn/kernel-hydrogen/tools/include 
> -I/home/wn/kernel-hydrogen/tools/arch/x86/include/uapi 
> -I/home/wn/kernel-hydrogen/tools/include/uapi    libbpf.c all   -o libbpf
>  gcc: error: all: No such file or directory
>  make: *** [libbpf] Error 1
>
> Thank you.

It is not 'caused' by your patch. 'make libbpf' fails without
your change because it tries to build an executable from
libbpf.c, but main() is missing.

I think libbpf should never be used as a make target. Your
new dependency looks strange.

Thank you.

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#1539584

FromJoe Stringer <joe@ovn.org>
Date2016-12-09 19:10 +0100
Message-ID<sMxMl-6wk-35@gated-at.bofh.it>
In reply to#1539090
On 8 December 2016 at 21:18, Wangnan (F) <wangnan0@huawei.com> wrote:
>
>
> On 2016/12/9 13:04, Wangnan (F) wrote:
>>
>>
>>
>> On 2016/12/9 10:46, Joe Stringer wrote:
>>
>> [SNIP]
>>
>>>   diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
>>> index 62d89d50fcbd..616bd55f3be8 100644
>>> --- a/tools/lib/bpf/Makefile
>>> +++ b/tools/lib/bpf/Makefile
>>> @@ -149,6 +149,8 @@ CMD_TARGETS = $(LIB_FILE)
>>>     TARGETS = $(CMD_TARGETS)
>>>   +libbpf: all
>>> +
>>
>>
>> Why we need this? I tested this patch without it and it seems to work, and
>> this line causes an extra error:
>>  $ pwd
>>  /home/wn/kernel/tools/lib/bpf
>>  $ make libbpf
>>  ...
>>  gcc -g -Wall -DHAVE_LIBELF_MMAP_SUPPORT -DHAVE_ELF_GETPHDRNUM_SUPPORT
>> -Wbad-function-cast -Wdeclaration-after-statement -Wformat-security
>> -Wformat-y2k -Winit-self -Wmissing-declarations -Wmissing-prototypes
>> -Wnested-externs -Wno-system-headers -Wold-style-definition -Wpacked
>> -Wredundant-decls -Wshadow -Wstrict-aliasing=3 -Wstrict-prototypes
>> -Wswitch-default -Wswitch-enum -Wundef -Wwrite-strings -Wformat -Werror
>> -Wall -fPIC -I. -I/home/wn/kernel-hydrogen/tools/include
>> -I/home/wn/kernel-hydrogen/tools/arch/x86/include/uapi
>> -I/home/wn/kernel-hydrogen/tools/include/uapi    libbpf.c all   -o libbpf
>>  gcc: error: all: No such file or directory
>>  make: *** [libbpf] Error 1
>>
>> Thank you.
>
>
> It is not 'caused' by your patch. 'make libbpf' fails without
> your change because it tries to build an executable from
> libbpf.c, but main() is missing.
>
> I think libbpf should never be used as a make target. Your
> new dependency looks strange.

Thanks for the feedback, I sent a patch to address this on top of perf/core:

https://lkml.org/lkml/2016/12/9/518

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