[RFC PATCH bpf-next 1/3] bpf: Add BPF debug mode

[Juntong Deng]

This patch adds BPF debug mode.

When a bpf program is in debug mode, all calls to kfuncs and helpers are
traced and output to the trace ring buffer, including arguments and
return values, in a strace-like format.

Signed-off-by: Juntong Deng <juntong.deng@xxxxxxxxxxx>
---
 include/linux/bpf.h            | 3 ++-
 include/uapi/linux/bpf.h       | 1 +
 kernel/bpf/syscall.c           | 4 +++-
 tools/include/uapi/linux/bpf.h | 2 ++
 tools/lib/bpf/libbpf.c         | 6 ++++++
 tools/lib/bpf/libbpf.h         | 2 ++
 6 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 1bc90d805872..c8585b436d0b 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1614,7 +1614,8 @@ struct bpf_prog {
 				call_get_stack:1, /* Do we call bpf_get_stack() or bpf_get_stackid() */
 				call_get_func_ip:1, /* Do we call get_func_ip() */
 				tstamp_type_access:1, /* Accessed __sk_buff->tstamp_type */
-				sleepable:1;	/* BPF program is sleepable */
+				sleepable:1,	/* BPF program is sleepable */
+				debug_mode:1;
 	enum bpf_prog_type	type;		/* Type of BPF program */
 	enum bpf_attach_type	expected_attach_type; /* For some prog types */
 	u32			len;		/* Number of filter blocks */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index fff6cdb8d11a..6c68a16a5549 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1272,6 +1272,7 @@ enum bpf_perf_event_type {
 /* The verifier internal test flag. Behavior is undefined */
 #define BPF_F_TEST_REG_INVARIANTS	(1U << 7)
 
+#define BPF_F_DEBUG_MODE	(1U << 8)
 /* link_create.kprobe_multi.flags used in LINK_CREATE command for
  * BPF_TRACE_KPROBE_MULTI attach type to create return probe.
  */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index c420edbfb7c8..1261315c2410 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2757,7 +2757,8 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
 				 BPF_F_XDP_HAS_FRAGS |
 				 BPF_F_XDP_DEV_BOUND_ONLY |
 				 BPF_F_TEST_REG_INVARIANTS |
-				 BPF_F_TOKEN_FD))
+				 BPF_F_TOKEN_FD |
+				 BPF_F_DEBUG_MODE))
 		return -EINVAL;
 
 	bpf_prog_load_fixup_attach_type(attr);
@@ -2870,6 +2871,7 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
 
 	prog->expected_attach_type = attr->expected_attach_type;
 	prog->sleepable = !!(attr->prog_flags & BPF_F_SLEEPABLE);
+	prog->debug_mode = !!(attr->prog_flags & BPF_F_DEBUG_MODE);
 	prog->aux->attach_btf = attach_btf;
 	prog->aux->attach_btf_id = attr->attach_btf_id;
 	prog->aux->dst_prog = dst_prog;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index fff6cdb8d11a..3b700cb86836 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1272,6 +1272,8 @@ enum bpf_perf_event_type {
 /* The verifier internal test flag. Behavior is undefined */
 #define BPF_F_TEST_REG_INVARIANTS	(1U << 7)
 
+#define BPF_F_DEBUG_MODE	(1U << 8)
+
 /* link_create.kprobe_multi.flags used in LINK_CREATE command for
  * BPF_TRACE_KPROBE_MULTI attach type to create return probe.
  */
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 194809da5172..2ff3f2a597b3 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -689,6 +689,7 @@ struct bpf_object {
 	bool loaded;
 	bool has_subcalls;
 	bool has_rodata;
+	bool debug_mode;
 
 	struct bpf_gen *gen_loader;
 
@@ -7520,6 +7521,8 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
 	load_attr.log_level = log_level;
 	load_attr.prog_flags = prog->prog_flags;
 	load_attr.fd_array = obj->fd_array;
+	if (obj->debug_mode)
+		load_attr.prog_flags |= BPF_F_DEBUG_MODE;
 
 	load_attr.token_fd = obj->token_fd;
 	if (obj->token_fd)
@@ -7972,6 +7975,7 @@ static struct bpf_object *bpf_object_open(const char *path, const void *obj_buf,
 	char *log_buf;
 	size_t log_size;
 	__u32 log_level;
+	bool debug_mode;
 
 	if (obj_buf && !obj_name)
 		return ERR_PTR(-EINVAL);
@@ -7996,6 +8000,7 @@ static struct bpf_object *bpf_object_open(const char *path, const void *obj_buf,
 	log_buf = OPTS_GET(opts, kernel_log_buf, NULL);
 	log_size = OPTS_GET(opts, kernel_log_size, 0);
 	log_level = OPTS_GET(opts, kernel_log_level, 0);
+	debug_mode = OPTS_GET(opts, debug_mode, false);
 	if (log_size > UINT_MAX)
 		return ERR_PTR(-EINVAL);
 	if (log_size && !log_buf)
@@ -8018,6 +8023,7 @@ static struct bpf_object *bpf_object_open(const char *path, const void *obj_buf,
 	obj->log_buf = log_buf;
 	obj->log_size = log_size;
 	obj->log_level = log_level;
+	obj->debug_mode = debug_mode;
 
 	if (token_path) {
 		obj->token_path = strdup(token_path);
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 3020ee45303a..191547045b7e 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -123,6 +123,8 @@ struct bpf_object_open_opts {
 	 */
 	const char *object_name;
 	/* parse map definitions non-strictly, allowing extra attributes/data */
+	bool debug_mode;
+	/* open debug mode */
 	bool relaxed_maps;
 	/* maps that set the 'pinning' attribute in their definition will have
 	 * their pin_path attribute set to a file in this directory, and be
-- 
2.39.5