netdev - [RFC PATCH v11 bpf-next 06/14] bpf: Remove recursion call in btf_struct

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Date:   Sun,  9 Aug 2020 17:02:54 +0200
From:   Jiri Olsa <jolsa@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Martin KaFai Lau <kafai@...com>,
        David Miller <davem@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Wenbo Zhang <ethercflow@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Brendan Gregg <bgregg@...flix.com>,
        Florent Revest <revest@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: [RFC PATCH v11 bpf-next 06/14] bpf: Remove recursion call in btf_struct_access

Andrii suggested we can simply jump to again label
instead of making recursion call.

Suggested-by: Andrii Nakryiko <andriin@...com>
Acked-by: Andrii Nakryiko <andriin@...com>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 kernel/bpf/btf.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index ee0e2a5e6c88..4488c5b03941 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3931,14 +3931,13 @@ int btf_struct_access(struct bpf_verifier_log *log,
 		/* Only allow structure for now, can be relaxed for
 		 * other types later.
 		 */
-		elem_type = btf_type_skip_modifiers(btf_vmlinux,
-						    array_elem->type, NULL);
-		if (!btf_type_is_struct(elem_type))
+		t = btf_type_skip_modifiers(btf_vmlinux, array_elem->type,
+					    NULL);
+		if (!btf_type_is_struct(t))
 			goto error;
 
-		off = (off - moff) % elem_type->size;
-		return btf_struct_access(log, elem_type, off, size, atype,
-					 next_btf_id);
+		off = (off - moff) % t->size;
+		goto again;
 
 error:
 		bpf_log(log, "access beyond struct %s at off %u size %u\n",
-- 
2.25.4