From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yonghong Song Subject: [PATCH bpf] tools: bpftool: fix a bitfield pretty print issue Date: Wed, 28 Nov 2018 09:38:23 -0800 Message-ID: <20181128173823.547847-1-yhs@fb.com> Mime-Version: 1.0 Content-Type: text/plain Cc: To: , , , Return-path: Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:43964 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728163AbeK2Els (ORCPT ); Wed, 28 Nov 2018 23:41:48 -0500 Received: from pps.filterd (m0109333.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wASHbJbM020645 for ; Wed, 28 Nov 2018 09:39:24 -0800 Received: from maileast.thefacebook.com ([199.201.65.23]) by mx0a-00082601.pphosted.com with ESMTP id 2p1wjy8fs5-7 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-SHA384 bits=256 verify=NOT) for ; Wed, 28 Nov 2018 09:39:23 -0800 Sender: netdev-owner@vger.kernel.org List-ID: Commit b12d6ec09730 ("bpf: btf: add btf print functionality") added btf pretty print functionality to bpftool. There is a problem though in printing a bitfield whose type has modifiers. For example, for a type like typedef int ___int; struct tmp_t { int a:3; ___int b:3; }; Suppose we have a map struct bpf_map_def SEC("maps") tmpmap = { .type = BPF_MAP_TYPE_HASH, .key_size = sizeof(__u32), .value_size = sizeof(struct tmp_t), .max_entries = 1, }; and the hash table is populated with one element with key 0 and value (.a = 1 and .b = 2). In BTF, the struct member "b" will have a type "typedef" which points to an int type. The current implementation does not pass the bit offset during transition from typedef to int type, hence incorrectly print the value as $ bpftool m d id 79 [{ "key": 0, "value": { "a": 0x1, "b": 0x1 } } ] This patch fixed the issue by carrying bit_offset along the type chain during bit_field print. The correct result can be printed as $ bpftool m d id 76 [{ "key": 0, "value": { "a": 0x1, "b": 0x2 } } ] The kernel pretty print is implemented correctly and does not have this issue. Fixes: b12d6ec09730 ("bpf: btf: add btf print functionality") Signed-off-by: Yonghong Song --- tools/bpf/bpftool/btf_dumper.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c index 55bc512a1831..e4e6e2b3fd84 100644 --- a/tools/bpf/bpftool/btf_dumper.c +++ b/tools/bpf/bpftool/btf_dumper.c @@ -32,7 +32,7 @@ static void btf_dumper_ptr(const void *data, json_writer_t *jw, } static int btf_dumper_modifier(const struct btf_dumper *d, __u32 type_id, - const void *data) + __u8 bit_offset, const void *data) { int actual_type_id; @@ -40,7 +40,7 @@ static int btf_dumper_modifier(const struct btf_dumper *d, __u32 type_id, if (actual_type_id < 0) return actual_type_id; - return btf_dumper_do_type(d, actual_type_id, 0, data); + return btf_dumper_do_type(d, actual_type_id, bit_offset, data); } static void btf_dumper_enum(const void *data, json_writer_t *jw) @@ -237,7 +237,7 @@ static int btf_dumper_do_type(const struct btf_dumper *d, __u32 type_id, case BTF_KIND_VOLATILE: case BTF_KIND_CONST: case BTF_KIND_RESTRICT: - return btf_dumper_modifier(d, type_id, data); + return btf_dumper_modifier(d, type_id, bit_offset, data); default: jsonw_printf(d->jw, "(unsupported-kind"); return -EINVAL; -- 2.17.1