[v4,bpf-next,06/14] bpf: Use BTF_ID to resolve bpf_ctx_convert struct

This way the ID is resolved during compile time,
and we can remove the runtime name search.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 kernel/bpf/btf.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

On Thu, Jun 25, 2020 at 4:47 PM Jiri Olsa <jolsa@kernel.org> wrote:
>
> This way the ID is resolved during compile time,
> and we can remove the runtime name search.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---

This is a good improvement, but I was thinking about actually
simplifying btf_get_prog_ctx_type() logic itself (it also does all
this BTF ID resolution). But this is a nice first step, so:

Acked-by: Andrii Nakryiko <andriin@fb.com>


[...]

On 6/25/20 3:12 PM, Jiri Olsa wrote:
> This way the ID is resolved during compile time,
> and we can remove the runtime name search.
> 
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>   kernel/bpf/btf.c | 12 ++++++++----
>   1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 4da6b0770ff9..701a2cb5dfb2 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -18,6 +18,7 @@
>   #include <linux/sort.h>
>   #include <linux/bpf_verifier.h>
>   #include <linux/btf.h>
> +#include <linux/btf_ids.h>
>   #include <linux/skmsg.h>
>   #include <linux/perf_event.h>
>   #include <net/sock.h>
> @@ -3621,6 +3622,9 @@ static int btf_translate_to_vmlinux(struct bpf_verifier_log *log,
>   	return kern_ctx_type->type;
>   }
>   
> +BTF_ID_LIST(bpf_ctx_convert_btf_id)
> +BTF_ID(struct, bpf_ctx_convert)
> +
>   struct btf *btf_parse_vmlinux(void)
>   {
>   	struct btf_verifier_env *env = NULL;
> @@ -3659,10 +3663,10 @@ struct btf *btf_parse_vmlinux(void)
>   	if (err)
>   		goto errout;
>   
> -	/* find struct bpf_ctx_convert for type checking later */
> -	btf_id = btf_find_by_name_kind(btf, "bpf_ctx_convert", BTF_KIND_STRUCT);
> -	if (btf_id < 0) {
> -		err = btf_id;
> +	/* struct bpf_ctx_convert for type checking later */
> +	btf_id = bpf_ctx_convert_btf_id[0];
> +	if (btf_id <= 0) {

Just want to double check. Is it possible btf_id < 0 since previous 
patch did not check < 0?

> +		err = -EINVAL;
>   		goto errout;
>   	}
>   	/* btf_parse_vmlinux() runs under bpf_verifier_lock */
>

On Fri, Jun 26, 2020 at 02:44:39PM -0700, Yonghong Song wrote:
> 
> 
> On 6/25/20 3:12 PM, Jiri Olsa wrote:
> > This way the ID is resolved during compile time,
> > and we can remove the runtime name search.
> > 
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >   kernel/bpf/btf.c | 12 ++++++++----
> >   1 file changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 4da6b0770ff9..701a2cb5dfb2 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -18,6 +18,7 @@
> >   #include <linux/sort.h>
> >   #include <linux/bpf_verifier.h>
> >   #include <linux/btf.h>
> > +#include <linux/btf_ids.h>
> >   #include <linux/skmsg.h>
> >   #include <linux/perf_event.h>
> >   #include <net/sock.h>
> > @@ -3621,6 +3622,9 @@ static int btf_translate_to_vmlinux(struct bpf_verifier_log *log,
> >   	return kern_ctx_type->type;
> >   }
> > +BTF_ID_LIST(bpf_ctx_convert_btf_id)
> > +BTF_ID(struct, bpf_ctx_convert)
> > +
> >   struct btf *btf_parse_vmlinux(void)
> >   {
> >   	struct btf_verifier_env *env = NULL;
> > @@ -3659,10 +3663,10 @@ struct btf *btf_parse_vmlinux(void)
> >   	if (err)
> >   		goto errout;
> > -	/* find struct bpf_ctx_convert for type checking later */
> > -	btf_id = btf_find_by_name_kind(btf, "bpf_ctx_convert", BTF_KIND_STRUCT);
> > -	if (btf_id < 0) {
> > -		err = btf_id;
> > +	/* struct bpf_ctx_convert for type checking later */
> > +	btf_id = bpf_ctx_convert_btf_id[0];
> > +	if (btf_id <= 0) {
> 
> Just want to double check. Is it possible btf_id < 0 since previous patch
> did not check < 0?

right.. resolve_btfids would fail during linking,
so this is not necessary

thanks,
jirka