[PATCH bpf-next 0/2] libbpf: support modules in set_attach_target() API

[PATCH bpf-next 0/2] libbpf: support modules in set_attach_target() API

[Andrii Nakryiko]

Add support for finding BTF-based kernel attach targets (fentry/fexit
functions, tp_btf tracepoints, etc) with programmatic
bpf_program__set_attach_target() API. It is now as capable as libbpf's
SEC()-based logic.

Andrii Nakryiko (2):
  libbpf: support modules in bpf_program__set_attach_target() API
  selftests/bpf: add set_attach_target() API selftest for module target

 tools/lib/bpf/libbpf.c                        | 64 ++++++++++++-------
 .../selftests/bpf/prog_tests/module_attach.c  | 11 +++-
 .../selftests/bpf/progs/test_module_attach.c  | 11 ++++
 3 files changed, 61 insertions(+), 25 deletions(-)

-- 
2.24.1

[PATCH bpf-next 1/2] libbpf: support modules in bpf_program__set_attach_target() API

[Andrii Nakryiko]

Support finding kernel targets in kernel modules when using
bpf_program__set_attach_target() API. This brings it up to par with what
libbpf supports when doing declarative SEC()-based target determination.

Some minor internal refactoring was needed to make sure vmlinux BTF can be
loaded before bpf_object's load phase.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/libbpf.c | 64 ++++++++++++++++++++++++++----------------
 1 file changed, 40 insertions(+), 24 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 9be88a90a4aa..6ae748f6ea11 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2518,7 +2518,7 @@ static int bpf_object__finalize_btf(struct bpf_object *obj)
 	return 0;
 }
 
-static inline bool libbpf_prog_needs_vmlinux_btf(struct bpf_program *prog)
+static bool prog_needs_vmlinux_btf(struct bpf_program *prog)
 {
 	if (prog->type == BPF_PROG_TYPE_STRUCT_OPS ||
 	    prog->type == BPF_PROG_TYPE_LSM)
@@ -2533,37 +2533,43 @@ static inline bool libbpf_prog_needs_vmlinux_btf(struct bpf_program *prog)
 	return false;
 }
 
-static int bpf_object__load_vmlinux_btf(struct bpf_object *obj)
+static bool obj_needs_vmlinux_btf(const struct bpf_object *obj)
 {
-	bool need_vmlinux_btf = false;
 	struct bpf_program *prog;
-	int i, err;
+	int i;
 
 	/* CO-RE relocations need kernel BTF */
 	if (obj->btf_ext && obj->btf_ext->core_relo_info.len)
-		need_vmlinux_btf = true;
+		return true;
 
 	/* Support for typed ksyms needs kernel BTF */
 	for (i = 0; i < obj->nr_extern; i++) {
 		const struct extern_desc *ext;
 
 		ext = &obj->externs[i];
-		if (ext->type == EXT_KSYM && ext->ksym.type_id) {
-			need_vmlinux_btf = true;
-			break;
-		}
+		if (ext->type == EXT_KSYM && ext->ksym.type_id)
+			return true;
 	}
 
 	bpf_object__for_each_program(prog, obj) {
 		if (!prog->load)
 			continue;
-		if (libbpf_prog_needs_vmlinux_btf(prog)) {
-			need_vmlinux_btf = true;
-			break;
-		}
+		if (prog_needs_vmlinux_btf(prog))
+			return true;
 	}
 
-	if (!need_vmlinux_btf)
+	return false;
+}
+
+static int bpf_object__load_vmlinux_btf(struct bpf_object *obj, bool force)
+{
+	int err;
+
+	/* btf_vmlinux could be loaded earlier */
+	if (obj->btf_vmlinux)
+		return 0;
+
+	if (!force && !obj_needs_vmlinux_btf(obj))
 		return 0;
 
 	obj->btf_vmlinux = libbpf_find_kernel_btf();
@@ -7475,7 +7481,7 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
 	}
 
 	err = bpf_object__probe_loading(obj);
-	err = err ? : bpf_object__load_vmlinux_btf(obj);
+	err = err ? : bpf_object__load_vmlinux_btf(obj, false);
 	err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
 	err = err ? : bpf_object__sanitize_and_load_btf(obj);
 	err = err ? : bpf_object__sanitize_maps(obj);
@@ -10870,23 +10876,33 @@ int bpf_program__set_attach_target(struct bpf_program *prog,
 				   int attach_prog_fd,
 				   const char *attach_func_name)
 {
-	int btf_id;
+	int btf_obj_fd = 0, btf_id = 0, err;
 
 	if (!prog || attach_prog_fd < 0 || !attach_func_name)
 		return -EINVAL;
 
-	if (attach_prog_fd)
+	if (prog->obj->loaded)
+		return -EINVAL;
+
+	if (attach_prog_fd) {
 		btf_id = libbpf_find_prog_btf_id(attach_func_name,
 						 attach_prog_fd);
-	else
-		btf_id = libbpf_find_vmlinux_btf_id(attach_func_name,
-						    prog->expected_attach_type);
-
-	if (btf_id < 0)
-		return btf_id;
+		if (btf_id < 0)
+			return btf_id;
+	} else {
+		/* load btf_vmlinux, if not yet */
+		err = bpf_object__load_vmlinux_btf(prog->obj, true);
+		if (err)
+			return err;
+		err = find_kernel_btf_id(prog->obj, attach_func_name,
+					 prog->expected_attach_type,
+					 &btf_obj_fd, &btf_id);
+		if (err)
+			return err;
+	}
 
 	prog->attach_btf_id = btf_id;
-	prog->attach_btf_obj_fd = 0;
+	prog->attach_btf_obj_fd = btf_obj_fd;
 	prog->attach_prog_fd = attach_prog_fd;
 	return 0;
 }
-- 
2.24.1

[PATCH bpf-next 2/2] selftests/bpf: add set_attach_target() API selftest for module target

[Andrii Nakryiko]

Add test for bpf_program__set_attach_target() API, validating it can find
kernel module fentry target.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 .../testing/selftests/bpf/prog_tests/module_attach.c  | 11 ++++++++++-
 .../testing/selftests/bpf/progs/test_module_attach.c  | 11 +++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/module_attach.c b/tools/testing/selftests/bpf/prog_tests/module_attach.c
index 4b65e9918764..50796b651f72 100644
--- a/tools/testing/selftests/bpf/prog_tests/module_attach.c
+++ b/tools/testing/selftests/bpf/prog_tests/module_attach.c
@@ -28,10 +28,18 @@ void test_module_attach(void)
 	struct test_module_attach__bss *bss;
 	int err;
 
-	skel = test_module_attach__open_and_load();
+	skel = test_module_attach__open();
 	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
 		return;
 
+	err = bpf_program__set_attach_target(skel->progs.handle_fentry_manual,
+					     0, "bpf_testmod_test_read");
+	ASSERT_OK(err, "set_attach_target");
+
+	err = test_module_attach__load(skel);
+	if (CHECK(err, "skel_load", "failed to load skeleton\n"))
+		return;
+
 	bss = skel->bss;
 
 	err = test_module_attach__attach(skel);
@@ -44,6 +52,7 @@ void test_module_attach(void)
 	ASSERT_EQ(bss->raw_tp_read_sz, READ_SZ, "raw_tp");
 	ASSERT_EQ(bss->tp_btf_read_sz, READ_SZ, "tp_btf");
 	ASSERT_EQ(bss->fentry_read_sz, READ_SZ, "fentry");
+	ASSERT_EQ(bss->fentry_manual_read_sz, READ_SZ, "fentry_manual");
 	ASSERT_EQ(bss->fexit_read_sz, READ_SZ, "fexit");
 	ASSERT_EQ(bss->fexit_ret, -EIO, "fexit_tet");
 	ASSERT_EQ(bss->fmod_ret_read_sz, READ_SZ, "fmod_ret");
diff --git a/tools/testing/selftests/bpf/progs/test_module_attach.c b/tools/testing/selftests/bpf/progs/test_module_attach.c
index b563563df172..efd1e287ac17 100644
--- a/tools/testing/selftests/bpf/progs/test_module_attach.c
+++ b/tools/testing/selftests/bpf/progs/test_module_attach.c
@@ -38,6 +38,17 @@ int BPF_PROG(handle_fentry,
 	return 0;
 }
 
+__u32 fentry_manual_read_sz = 0;
+
+SEC("fentry/placeholder")
+int BPF_PROG(handle_fentry_manual,
+	     struct file *file, struct kobject *kobj,
+	     struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len)
+{
+	fentry_manual_read_sz = len;
+	return 0;
+}
+
 __u32 fexit_read_sz = 0;
 int fexit_ret = 0;
 
-- 
2.24.1

Re: [PATCH bpf-next 0/2] libbpf: support modules in set_attach_target() API

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (refs/heads/master):

On Fri, 11 Dec 2020 13:58:23 -0800 you wrote:
> Add support for finding BTF-based kernel attach targets (fentry/fexit
> functions, tp_btf tracepoints, etc) with programmatic
> bpf_program__set_attach_target() API. It is now as capable as libbpf's
> SEC()-based logic.
> 
> Andrii Nakryiko (2):
>   libbpf: support modules in bpf_program__set_attach_target() API
>   selftests/bpf: add set_attach_target() API selftest for module target
> 
> [...]

Here is the summary with links:
  - [bpf-next,1/2] libbpf: support modules in bpf_program__set_attach_target() API
    https://git.kernel.org/bpf/bpf-next/c/fe62de310e2b
  - [bpf-next,2/2] selftests/bpf: add set_attach_target() API selftest for module target
    https://git.kernel.org/bpf/bpf-next/c/2e33f831fccd

You are awesome, thank you!
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