netdev - [PATCH bpf-next 1/3] libbpf: fix struct end padding in btf

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Message-ID: <20191008231009.2991130-2-andriin@fb.com>
Date:   Tue, 8 Oct 2019 16:10:06 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>, <john.fastabend@...il.com>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: [PATCH bpf-next 1/3] libbpf: fix struct end padding in btf_dump

Fix a case where explicit padding at the end of a struct is necessary
due to non-standart alignment requirements of fields (which BTF doesn't
capture explicitly).

Fixes: 351131b51c7a ("libbpf: add btf_dump API for BTF-to-C conversion")
Reported-by: John Fastabend <john.fastabend@...il.com>
Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 tools/lib/bpf/btf_dump.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index ede55fec3618..87f27e2664c5 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -876,7 +876,6 @@ static void btf_dump_emit_struct_def(struct btf_dump *d,
 	__u16 vlen = btf_vlen(t);
 
 	packed = is_struct ? btf_is_struct_packed(d->btf, id, t) : 0;
-	align = packed ? 1 : btf_align_of(d->btf, id);
 
 	btf_dump_printf(d, "%s%s%s {",
 			is_struct ? "struct" : "union",
@@ -906,6 +905,13 @@ static void btf_dump_emit_struct_def(struct btf_dump *d,
 		btf_dump_printf(d, ";");
 	}
 
+	/* pad at the end, if necessary */
+	if (is_struct) {
+		align = packed ? 1 : btf_align_of(d->btf, id);
+		btf_dump_emit_bit_padding(d, off, t->size * 8, 0, align,
+					  lvl + 1);
+	}
+
 	if (vlen)
 		btf_dump_printf(d, "\n");
 	btf_dump_printf(d, "%s}", pfx(lvl));
-- 
2.17.1