linux-kernel - [PATCH 2/2] libbpf: fix dump of subsequent char arrays

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Date: Sat, 13 Apr 2024 23:12:58 +0200
From: Quentin Deslandes <qde@...cy.de>
To: bpf@...r.kernel.org
Cc: Andrii Nakryiko <andrii@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	Quentin Deslandes <qde@...cy.de>
Subject: [PATCH 2/2] libbpf: fix dump of subsequent char arrays

When dumping a character array, libbpf will watch for a '\0' and set
is_array_terminated=true if found. This prevents libbpf from printing
the remaining characters of the array, treating it as a nul-terminated
string.

However, once this flag is set, it's never reset, leading to subsequent
characters array not being printed properly:

str_multi = (__u8[2][16])[
    [
        'H',
        'e',
        'l',
    ],
],

This patch saves the is_array_terminated flag and restores its
default (false) value before looping over the elements of an array, then
restores it afterward. This way, libbpf's behavior is unchanged when
dumping the characters of an array, but subsequent arrays are printed
properly:

str_multi = (__u8[2][16])[
    [
        'H',
        'e',
        'l',
    ],
    [
        'l',
        'o',
    ],
],

Signed-off-by: Quentin Deslandes <qde@...cy.de>
---
 tools/lib/bpf/btf_dump.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 6a37e8517435..5dbca76b953f 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -2032,6 +2032,7 @@ static int btf_dump_array_data(struct btf_dump *d,
 	__u32 i, elem_type_id;
 	__s64 elem_size;
 	bool is_array_member;
+	bool is_array_terminated;
 
 	elem_type_id = array->type;
 	elem_type = skip_mods_and_typedefs(d->btf, elem_type_id, NULL);
@@ -2067,12 +2068,15 @@ static int btf_dump_array_data(struct btf_dump *d,
 	 */
 	is_array_member = d->typed_dump->is_array_member;
 	d->typed_dump->is_array_member = true;
+	is_array_terminated = d->typed_dump->is_array_terminated;
+	d->typed_dump->is_array_terminated = false;
 	for (i = 0; i < array->nelems; i++, data += elem_size) {
 		if (d->typed_dump->is_array_terminated)
 			break;
 		btf_dump_dump_type_data(d, NULL, elem_type, elem_type_id, data, 0, 0);
 	}
 	d->typed_dump->is_array_member = is_array_member;
+	d->typed_dump->is_array_terminated = is_array_terminated;
 	d->typed_dump->depth--;
 	btf_dump_data_pfx(d);
 	btf_dump_type_values(d, "]");
-- 
2.44.0