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Date:   Sun, 15 Mar 2020 17:56:12 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     <bpf@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>,
        <netdev@...r.kernel.org>
Subject: [PATCH bpf-next 2/4] bpftool: Print as a string for char array

A char[] is currently printed as an integer array.
This patch will print it as a string when
1) The array element type is an one byte int
2) The array element type has a BTF_INT_CHAR encoding or
   the array element type's name is "char"
3) All characters is between (0x1f, 0x7f) and it is terminated
   by a null character.

Signed-off-by: Martin KaFai Lau <kafai@...com>
---
 tools/bpf/bpftool/btf_dumper.c | 41 ++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
index 57bd6c0fafc9..1d2d8d2cedea 100644
--- a/tools/bpf/bpftool/btf_dumper.c
+++ b/tools/bpf/bpftool/btf_dumper.c
@@ -77,6 +77,42 @@ static void btf_dumper_enum(const struct btf_dumper *d,
 	jsonw_int(d->jw, value);
 }
 
+static bool is_str_array(const struct btf *btf, const struct btf_array *arr,
+			 const char *s)
+{
+	const struct btf_type *elem_type;
+	const char *end_s;
+
+	if (!arr->nelems)
+		return false;
+
+	elem_type = btf__type_by_id(btf, arr->type);
+	/* Not skipping typedef.  typedef to char does not count as
+	 * a string now.
+	 */
+	while (elem_type && btf_is_mod(elem_type))
+		elem_type = btf__type_by_id(btf, elem_type->type);
+
+	if (!elem_type || !btf_is_int(elem_type) || elem_type->size != 1)
+		return false;
+
+	if (btf_int_encoding(elem_type) != BTF_INT_CHAR &&
+	    strcmp("char", btf__name_by_offset(btf, elem_type->name_off)))
+		return false;
+
+	end_s = s + arr->nelems;
+	while (s < end_s) {
+		if (!*s)
+			return true;
+		if (*s <= 0x1f || *s >= 0x7f)
+			return false;
+		s++;
+	}
+
+	/* '\0' is not found */
+	return false;
+}
+
 static int btf_dumper_array(const struct btf_dumper *d, __u32 type_id,
 			    const void *data)
 {
@@ -86,6 +122,11 @@ static int btf_dumper_array(const struct btf_dumper *d, __u32 type_id,
 	int ret = 0;
 	__u32 i;
 
+	if (is_str_array(d->btf, arr, data)) {
+		jsonw_string(d->jw, data);
+		return 0;
+	}
+
 	elem_size = btf__resolve_size(d->btf, arr->type);
 	if (elem_size < 0)
 		return elem_size;
-- 
2.17.1

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