[PATCH bpf-next v4 2/2] perf: stop using deprecated bpf_object__next() API

[Christy Lee <christylee@fb.com>]

Libbpf has deprecated the ability to keep track of object list inside
libbpf, it now requires applications to track usage multiple bpf
objects directly. Remove usage of bpf_object__next() API  and hoist the
tracking logic to perf.

Committer note:

This is tested by following the committer's note in the original commit
"aa3abf30bb28addcf593578d37447d42e3f65fc3".

I ran 'perf test -v LLVM' and used it's output to generate a script for
compiling the perf test object:

--------------------------------------------------
$ cat ~/bin/hello-ebpf
INPUT_FILE=/tmp/test.c
OUTPUT_FILE=/tmp/test.o

export KBUILD_DIR=/lib/modules/5.12.0-0_fbk2_3390_g7ecb4ac46d7f/build
export NR_CPUS=56
export LINUX_VERSION_CODE=0x50c00
export CLANG_EXEC=/data/users/christylee/devtools/llvm/latest/bin/clang
export CLANG_OPTIONS=-xc
export KERNEL_INC_OPTIONS="KERNEL_INC_OPTIONS= -nostdinc \
-isystem /usr/lib/gcc/x86_64-redhat-linux/8/include -I./arch/x86/include \
-I./arch/x86/include/generated  -I./include -I./arch/x86/include/uapi \
-I./arch/x86/include/generated/uapi -I./include/uapi \
-I./include/generated/uapi -include ./include/linux/compiler-version.h \
-include ./include/linux/kconfig.h"
export PERF_BPF_INC_OPTIONS=-I/usr/lib/perf/include/bpf
export WORKING_DIR=/lib/modules/5.12.0-0_fbk2_3390_g7ecb4ac46d7f/build
export CLANG_SOURCE=-

rm -f $OUTPUT_FILE
cat $INPUT_FILE | /data/users/christylee/devtools/llvm/latest/bin/clang \
-D__KERNEL__ -D__NR_CPUS__=56 -DLINUX_VERSION_CODE=0x50c00 -xc  \
-I/usr/lib/perf/include/bpf -nostdinc \
-isystem /usr/lib/gcc/x86_64-redhat-linux/8/include -I./arch/x86/include \
-I./arch/x86/include/generated  -I./include -I./arch/x86/include/uapi \
-I./arch/x86/include/generated/uapi -I./include/uapi \
-I./include/generated/uapi -include ./include/linux/compiler-version.h \
-include ./include/linux/kconfig.h -Wno-unused-value -Wno-pointer-sign \
-working-directory /lib/modules/5.12.0-0_fbk2_3390_g7ecb4ac46d7f/build \
-c - -target bpf -O2 -o $OUTPUT_FILE
--------------------------------------------------

I then wrote and compiled a script that ask to get asks to put a probe
at a function that
does not exists in the kernel, it errors out as expected:

$ cat /tmp/test.c
__attribute__((section("probe_point=not_exist"), used))
int probe_point(void *ctx) {
    return 0;
}
char _license[] __attribute__((section("license"), used)) = "GPL";
int _version __attribute__((section("version"), used)) = 0x40100;

$ cd ~/bin && ./hello-ebpf
$ ./perf record --event /tmp/test.o sleep 1

Probe point 'not_exist' not found.
event syntax error: '/tmp/test.o'
                     \___ You need to check probing points in BPF file

(add -v to see detail)
Run 'perf list' for a list of valid events

 Usage: perf record [<options>] [<command>]
    or: perf record [<options>] -- <command> [<options>]

    -e, --event <event>   event selector. use 'perf list' to list
available events

---------------------------------------------------

Next I changed the attribute to something that exists in the kernel.
As expected, it errors out
with permission problem:
$ cat /tmp/test.c
__attribute__((section("probe_point=kernel_execve"), used))
int probe_point(void *ctx) {
    return 0;
}
char _license[] __attribute__((section("license"), used)) = "GPL";
int _version __attribute__((section("version"), used)) = 0x40100;

$ grep kernel_execve /proc/kallsyms
ffffffff812dc210 T kernel_execve

$ cd ~/bin && ./hello-ebpf
$ ./perf record --event /tmp/test.o sleep 1

Failed to open kprobe_events: Permission denied
event syntax error: '/tmp/test.o'
                     \___ You need to be root

(add -v to see detail)
Run 'perf list' for a list of valid events

 Usage: perf record [<options>] [<command>]
    or: perf record [<options>] -- <command> [<options>]

    -e, --event <event>   event selector. use 'perf list' to list
available events

---------------------------------------------------

Reran as root, see that the probe point worked as intended.

$ sudo -i
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.018 MB perf.data ]
perf_bpf_probe:probe_point
perf_bpf_probe:probe_point: type: 2, size: 128, config: 0x8e9, \
{ sample_period, sample_freq }: 1, \
sample_type: IP|TID|TIME|CPU|PERIOD|RAW, read_format: ID, disabled: 1, \
inherit: 1, mmap: 1, comm: 1, enable_on_exec: 1, task: 1, \
sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, \
bpf_event: 1

---------------------------------------------------

Signed-off-by: Christy Lee <christylee@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/perf/util/bpf-loader.c | 72 +++++++++++++++++++++++++++---------
 tools/perf/util/bpf-loader.h |  1 +
 2 files changed, 55 insertions(+), 18 deletions(-)

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index 4631cac3957f..b1822f8af2bb 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -29,9 +29,6 @@
 
 #include <internal/xyarray.h>
 
-/* temporarily disable libbpf deprecation warnings */
-#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
-
 static int libbpf_perf_print(enum libbpf_print_level level __attribute__((unused)),
 			      const char *fmt, va_list args)
 {
@@ -49,6 +46,36 @@ struct bpf_prog_priv {
 	int *type_mapping;
 };
 
+struct bpf_perf_object {
+	struct bpf_object *obj;
+	struct list_head list;
+};
+
+static LIST_HEAD(bpf_objects_list);
+
+struct bpf_perf_object *bpf_perf_object__next(struct bpf_perf_object *prev)
+{
+	struct bpf_perf_object *next;
+
+	if (!prev)
+		next = list_first_entry(&bpf_objects_list,
+					struct bpf_perf_object, list);
+	else
+		next = list_next_entry(prev, list);
+
+	/* Empty list is noticed here so don't need checking on entry. */
+	if (&next->list == &bpf_objects_list)
+		return NULL;
+
+	return next;
+}
+
+#define bpf_perf_object__for_each(perf_obj, tmp, obj)                          \
+	for ((perf_obj) = bpf_perf_object__next(NULL),                         \
+	    (tmp) = bpf_perf_object__next(perf_obj), (obj) = NULL;             \
+	     (perf_obj) != NULL; (perf_obj) = (tmp),                           \
+	    (tmp) = bpf_perf_object__next(tmp), (obj) = (perf_obj)->obj)
+
 static bool libbpf_initialized;
 
 struct bpf_object *
@@ -113,9 +140,10 @@ struct bpf_object *bpf__prepare_load(const char *filename, bool source)
 
 void bpf__clear(void)
 {
-	struct bpf_object *obj, *tmp;
+	struct bpf_perf_object *perf_obj, *tmp;
+	struct bpf_object *obj;
 
-	bpf_object__for_each_safe(obj, tmp) {
+	bpf_perf_object__for_each(perf_obj, tmp, obj) {
 		bpf__unprobe(obj);
 		bpf_object__close(obj);
 	}
@@ -621,8 +649,12 @@ static int hook_load_preprocessor(struct bpf_program *prog)
 	if (err)
 		return err;
 
+/* temporarily disable libbpf deprecation warnings */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 	err = bpf_program__set_prep(prog, priv->nr_types,
 				    preproc_gen_prologue);
+#pragma GCC diagnostic pop
 	return err;
 }
 
@@ -776,7 +808,11 @@ int bpf__foreach_event(struct bpf_object *obj,
 			if (priv->need_prologue) {
 				int type = priv->type_mapping[i];
 
+/* temporarily disable libbpf deprecation warnings */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 				fd = bpf_program__nth_fd(prog, type);
+#pragma GCC diagnostic pop
 			} else {
 				fd = bpf_program__fd(prog);
 			}
@@ -1488,10 +1524,11 @@ apply_obj_config_object(struct bpf_object *obj)
 
 int bpf__apply_obj_config(void)
 {
-	struct bpf_object *obj, *tmp;
+	struct bpf_perf_object *perf_obj, *tmp;
+	struct bpf_object *obj;
 	int err;
 
-	bpf_object__for_each_safe(obj, tmp) {
+	bpf_perf_object__for_each(perf_obj, tmp, obj) {
 		err = apply_obj_config_object(obj);
 		if (err)
 			return err;
@@ -1500,26 +1537,25 @@ int bpf__apply_obj_config(void)
 	return 0;
 }
 
-#define bpf__for_each_map(pos, obj, objtmp)	\
-	bpf_object__for_each_safe(obj, objtmp)	\
-		bpf_object__for_each_map(pos, obj)
+#define bpf__perf_for_each_map(perf_obj, tmp, obj, map)                        \
+	bpf_perf_object__for_each(perf_obj, tmp, obj)                          \
+		bpf_object__for_each_map(map, obj)
 
-#define bpf__for_each_map_named(pos, obj, objtmp, name)	\
-	bpf__for_each_map(pos, obj, objtmp) 		\
-		if (bpf_map__name(pos) && 		\
-			(strcmp(name, 			\
-				bpf_map__name(pos)) == 0))
+#define bpf__perf_for_each_map_named(perf_obj, tmp, obj, map, name)            \
+	bpf__perf_for_each_map(perf_obj, tmp, obj, map)                        \
+		if (bpf_map__name(map) && (strcmp(name, bpf_map__name(map)) == 0))
 
 struct evsel *bpf__setup_output_event(struct evlist *evlist, const char *name)
 {
 	struct bpf_map_priv *tmpl_priv = NULL;
-	struct bpf_object *obj, *tmp;
+	struct bpf_perf_object *perf_obj, *tmp;
+	struct bpf_object *obj;
 	struct evsel *evsel = NULL;
 	struct bpf_map *map;
 	int err;
 	bool need_init = false;
 
-	bpf__for_each_map_named(map, obj, tmp, name) {
+	bpf__perf_for_each_map_named(perf_obj, tmp, obj, map, name) {
 		struct bpf_map_priv *priv = bpf_map__priv(map);
 
 		if (IS_ERR(priv))
@@ -1555,7 +1591,7 @@ struct evsel *bpf__setup_output_event(struct evlist *evlist, const char *name)
 		evsel = evlist__last(evlist);
 	}
 
-	bpf__for_each_map_named(map, obj, tmp, name) {
+	bpf__perf_for_each_map_named(perf_obj, tmp, obj, map, name) {
 		struct bpf_map_priv *priv = bpf_map__priv(map);
 
 		if (IS_ERR(priv))
diff --git a/tools/perf/util/bpf-loader.h b/tools/perf/util/bpf-loader.h
index 5d1c725cea29..95262b7e936f 100644
--- a/tools/perf/util/bpf-loader.h
+++ b/tools/perf/util/bpf-loader.h
@@ -53,6 +53,7 @@ typedef int (*bpf_prog_iter_callback_t)(const char *group, const char *event,
 
 #ifdef HAVE_LIBBPF_SUPPORT
 struct bpf_object *bpf__prepare_load(const char *filename, bool source);
+struct bpf_perf_object *bpf_perf_object__next(struct bpf_perf_object *prev);
 int bpf__strerror_prepare_load(const char *filename, bool source,
 			       int err, char *buf, size_t size);
 
-- 
2.30.2