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[bpf-next,1/2] libbpf: support "module:function" syntax for tracing programs

Message ID 239e6c07800fa0c6c7540589e6ba0a49ba419237.1714133551.git.vmalik@redhat.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series libbpf: support "module:function" syntax for tracing programs | expand

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Commit Message

Viktor Malik April 26, 2024, 12:17 p.m. UTC
In some situations, it is useful to explicitly specify a kernel module
to search for a tracing program target (e.g. when a function of the same
name exists in multiple modules or in vmlinux).

This patch enables that by allowing the "module:function" syntax for the
find_kernel_btf_id function. Thanks to this, the syntax can be used both
from a SEC macro (i.e. `SEC(fentry/module:function)`) and via the
bpf_program__set_attach_target API call.

Signed-off-by: Viktor Malik <vmalik@redhat.com>
---
 tools/lib/bpf/libbpf.c | 33 ++++++++++++++++++++++++---------
 1 file changed, 24 insertions(+), 9 deletions(-)

Comments

Andrii Nakryiko April 29, 2024, 8:10 p.m. UTC | #1
On Fri, Apr 26, 2024 at 5:17 AM Viktor Malik <vmalik@redhat.com> wrote:
>
> In some situations, it is useful to explicitly specify a kernel module
> to search for a tracing program target (e.g. when a function of the same
> name exists in multiple modules or in vmlinux).
>
> This patch enables that by allowing the "module:function" syntax for the
> find_kernel_btf_id function. Thanks to this, the syntax can be used both
> from a SEC macro (i.e. `SEC(fentry/module:function)`) and via the
> bpf_program__set_attach_target API call.
>
> Signed-off-by: Viktor Malik <vmalik@redhat.com>
> ---
>  tools/lib/bpf/libbpf.c | 33 ++++++++++++++++++++++++---------
>  1 file changed, 24 insertions(+), 9 deletions(-)
>

Looks good, just stylistic nits below.

> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 97eb6e5dd7c8..5a136876cd1c 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9858,16 +9858,28 @@ static int find_kernel_btf_id(struct bpf_object *obj, const char *attach_name,
>                               enum bpf_attach_type attach_type,
>                               int *btf_obj_fd, int *btf_type_id)
>  {
> -       int ret, i;
> +       int ret, i, mod_len;
> +       const char *fun_name, *mod_name = NULL;

bikeshedding nit, but let's call it fn_name ("fun" doesn't associate
with "function" in my head at all)

>
> -       ret = find_attach_btf_id(obj->btf_vmlinux, attach_name, attach_type);
> -       if (ret > 0) {
> -               *btf_obj_fd = 0; /* vmlinux BTF */
> -               *btf_type_id = ret;
> -               return 0;
> +       fun_name = strchr(attach_name, ':');
> +       if (fun_name) {
> +               mod_name = attach_name;
> +               mod_len = fun_name - mod_name;
> +               fun_name++;
> +       }
> +
> +       if (!mod_name || strncmp(mod_name, "vmlinux", mod_len) == 0) {
> +               ret = find_attach_btf_id(obj->btf_vmlinux,
> +                                        mod_name ? fun_name : attach_name,
> +                                        attach_type);
> +               if (ret > 0) {
> +                       *btf_obj_fd = 0; /* vmlinux BTF */
> +                       *btf_type_id = ret;
> +                       return 0;
> +               }
> +               if (ret != -ENOENT)
> +                       return ret;
>         }
> -       if (ret != -ENOENT)
> -               return ret;
>
>         ret = load_module_btfs(obj);
>         if (ret)
> @@ -9876,7 +9888,10 @@ static int find_kernel_btf_id(struct bpf_object *obj, const char *attach_name,
>         for (i = 0; i < obj->btf_module_cnt; i++) {
>                 const struct module_btf *mod = &obj->btf_modules[i];
>
> -               ret = find_attach_btf_id(mod->btf, attach_name, attach_type);
> +               if (mod_name && strncmp(mod->name, mod_name, mod_len))

please add explicit `== 0` after strncmp(), like you did above for vmlinux

> +                       continue;
> +
> +               ret = find_attach_btf_id(mod->btf, mod_name ? fun_name : attach_name, attach_type);
>                 if (ret > 0) {
>                         *btf_obj_fd = mod->fd;
>                         *btf_type_id = ret;
> --
> 2.44.0
>
diff mbox series

Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 97eb6e5dd7c8..5a136876cd1c 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9858,16 +9858,28 @@  static int find_kernel_btf_id(struct bpf_object *obj, const char *attach_name,
 			      enum bpf_attach_type attach_type,
 			      int *btf_obj_fd, int *btf_type_id)
 {
-	int ret, i;
+	int ret, i, mod_len;
+	const char *fun_name, *mod_name = NULL;
 
-	ret = find_attach_btf_id(obj->btf_vmlinux, attach_name, attach_type);
-	if (ret > 0) {
-		*btf_obj_fd = 0; /* vmlinux BTF */
-		*btf_type_id = ret;
-		return 0;
+	fun_name = strchr(attach_name, ':');
+	if (fun_name) {
+		mod_name = attach_name;
+		mod_len = fun_name - mod_name;
+		fun_name++;
+	}
+
+	if (!mod_name || strncmp(mod_name, "vmlinux", mod_len) == 0) {
+		ret = find_attach_btf_id(obj->btf_vmlinux,
+					 mod_name ? fun_name : attach_name,
+					 attach_type);
+		if (ret > 0) {
+			*btf_obj_fd = 0; /* vmlinux BTF */
+			*btf_type_id = ret;
+			return 0;
+		}
+		if (ret != -ENOENT)
+			return ret;
 	}
-	if (ret != -ENOENT)
-		return ret;
 
 	ret = load_module_btfs(obj);
 	if (ret)
@@ -9876,7 +9888,10 @@  static int find_kernel_btf_id(struct bpf_object *obj, const char *attach_name,
 	for (i = 0; i < obj->btf_module_cnt; i++) {
 		const struct module_btf *mod = &obj->btf_modules[i];
 
-		ret = find_attach_btf_id(mod->btf, attach_name, attach_type);
+		if (mod_name && strncmp(mod->name, mod_name, mod_len))
+			continue;
+
+		ret = find_attach_btf_id(mod->btf, mod_name ? fun_name : attach_name, attach_type);
 		if (ret > 0) {
 			*btf_obj_fd = mod->fd;
 			*btf_type_id = ret;