From: Alexei Starovoitov <ast@kernel.org>
Date: Mon, 20 Jan 2020 16:53:47 -0800
Subject: libbpf: Add support for program extensions
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Patch-mainline: v5.6-rc1
Git-commit: 2db6eab18b9778d55f48c804f8efebd7097e7958
References: bsc#1177028

Add minimal support for program extensions. bpf_object_open_opts() needs to be
called with attach_prog_fd = target_prog_fd and BPF program extension needs to
have in .c file section definition like SEC("freplace/func_to_be_replaced").
libbpf will search for "func_to_be_replaced" in the target_prog_fd's BTF and
will pass it in attach_btf_id to the kernel. This approach works for tests, but
more compex use case may need to request function name (and attach_btf_id that
kernel sees) to be more dynamic. Such API will be added in future patches.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20200121005348.2769920-3-ast@kernel.org
Acked-by: Gary Lin <glin@suse.com>
---
 tools/include/uapi/linux/bpf.h |    1 +
 tools/lib/bpf/bpf.c            |    3 ++-
 tools/lib/bpf/libbpf.c         |   13 ++++++++++---
 tools/lib/bpf/libbpf.h         |    2 ++
 tools/lib/bpf/libbpf.map       |    2 ++
 tools/lib/bpf/libbpf_probes.c  |    1 +
 6 files changed, 18 insertions(+), 4 deletions(-)

--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -176,6 +176,7 @@ enum bpf_prog_type {
 	BPF_PROG_TYPE_CGROUP_SOCKOPT,
 	BPF_PROG_TYPE_TRACING,
 	BPF_PROG_TYPE_STRUCT_OPS,
+	BPF_PROG_TYPE_EXT,
 };
 
 enum bpf_attach_type {
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -237,7 +237,8 @@ int bpf_load_program_xattr(const struct
 	attr.expected_attach_type = load_attr->expected_attach_type;
 	if (attr.prog_type == BPF_PROG_TYPE_STRUCT_OPS) {
 		attr.attach_btf_id = load_attr->attach_btf_id;
-	} else if (attr.prog_type == BPF_PROG_TYPE_TRACING) {
+	} else if (attr.prog_type == BPF_PROG_TYPE_TRACING ||
+		   attr.prog_type == BPF_PROG_TYPE_EXT) {
 		attr.attach_btf_id = load_attr->attach_btf_id;
 		attr.attach_prog_fd = load_attr->attach_prog_fd;
 	} else {
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4704,7 +4704,8 @@ load_program(struct bpf_program *prog, s
 	load_attr.license = license;
 	if (prog->type == BPF_PROG_TYPE_STRUCT_OPS) {
 		load_attr.attach_btf_id = prog->attach_btf_id;
-	} else if (prog->type == BPF_PROG_TYPE_TRACING) {
+	} else if (prog->type == BPF_PROG_TYPE_TRACING ||
+		   prog->type == BPF_PROG_TYPE_EXT) {
 		load_attr.attach_prog_fd = prog->attach_prog_fd;
 		load_attr.attach_btf_id = prog->attach_btf_id;
 	} else {
@@ -4789,7 +4790,8 @@ int bpf_program__load(struct bpf_program
 {
 	int err = 0, fd, i, btf_id;
 
-	if (prog->type == BPF_PROG_TYPE_TRACING) {
+	if (prog->type == BPF_PROG_TYPE_TRACING ||
+	    prog->type == BPF_PROG_TYPE_EXT) {
 		btf_id = libbpf_find_attach_btf_id(prog);
 		if (btf_id <= 0)
 			return btf_id;
@@ -4964,7 +4966,8 @@ __bpf_object__open(const char *path, con
 
 		bpf_program__set_type(prog, prog_type);
 		bpf_program__set_expected_attach_type(prog, attach_type);
-		if (prog_type == BPF_PROG_TYPE_TRACING)
+		if (prog_type == BPF_PROG_TYPE_TRACING ||
+		    prog_type == BPF_PROG_TYPE_EXT)
 			prog->attach_prog_fd = OPTS_GET(opts, attach_prog_fd, 0);
 	}
 
@@ -6025,6 +6028,7 @@ BPF_PROG_TYPE_FNS(xdp, BPF_PROG_TYPE_XDP
 BPF_PROG_TYPE_FNS(perf_event, BPF_PROG_TYPE_PERF_EVENT);
 BPF_PROG_TYPE_FNS(tracing, BPF_PROG_TYPE_TRACING);
 BPF_PROG_TYPE_FNS(struct_ops, BPF_PROG_TYPE_STRUCT_OPS);
+BPF_PROG_TYPE_FNS(extension, BPF_PROG_TYPE_EXT);
 
 enum bpf_attach_type
 bpf_program__get_expected_attach_type(struct bpf_program *prog)
@@ -6124,6 +6128,9 @@ static const struct bpf_sec_def section_
 		.expected_attach_type = BPF_TRACE_FEXIT,
 		.is_attach_btf = true,
 		.attach_fn = attach_trace),
+	SEC_DEF("freplace/", EXT,
+		.is_attach_btf = true,
+		.attach_fn = attach_trace),
 	BPF_PROG_SEC("xdp",			BPF_PROG_TYPE_XDP),
 	BPF_PROG_SEC("perf_event",		BPF_PROG_TYPE_PERF_EVENT),
 	BPF_PROG_SEC("lwt_in",			BPF_PROG_TYPE_LWT_IN),
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -347,6 +347,7 @@ LIBBPF_API int bpf_program__set_xdp(stru
 LIBBPF_API int bpf_program__set_perf_event(struct bpf_program *prog);
 LIBBPF_API int bpf_program__set_tracing(struct bpf_program *prog);
 LIBBPF_API int bpf_program__set_struct_ops(struct bpf_program *prog);
+LIBBPF_API int bpf_program__set_extension(struct bpf_program *prog);
 
 LIBBPF_API enum bpf_prog_type bpf_program__get_type(struct bpf_program *prog);
 LIBBPF_API void bpf_program__set_type(struct bpf_program *prog,
@@ -368,6 +369,7 @@ LIBBPF_API bool bpf_program__is_xdp(cons
 LIBBPF_API bool bpf_program__is_perf_event(const struct bpf_program *prog);
 LIBBPF_API bool bpf_program__is_tracing(const struct bpf_program *prog);
 LIBBPF_API bool bpf_program__is_struct_ops(const struct bpf_program *prog);
+LIBBPF_API bool bpf_program__is_extension(const struct bpf_program *prog);
 
 /*
  * No need for __attribute__((packed)), all members of 'bpf_map_def'
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -223,7 +223,9 @@ LIBBPF_0.0.7 {
 		bpf_prog_attach_xattr;
 		bpf_program__attach;
 		bpf_program__name;
+		bpf_program__is_extension;
 		bpf_program__is_struct_ops;
+		bpf_program__set_extension;
 		bpf_program__set_struct_ops;
 		btf__align_of;
 		libbpf_find_kernel_btf;
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -107,6 +107,7 @@ probe_load(enum bpf_prog_type prog_type,
 	case BPF_PROG_TYPE_CGROUP_SOCKOPT:
 	case BPF_PROG_TYPE_TRACING:
 	case BPF_PROG_TYPE_STRUCT_OPS:
+	case BPF_PROG_TYPE_EXT:
 	default:
 		break;
 	}