On Fri, Apr 26, 2024 at 5:17 AM Viktor Malik <vmalik@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
> 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
>
