[PATCH 4.19 135/243] tools: bpftool: fix a bitfield pretty print issue

Greg Kroah-Hartman
2019-12-11T15:21:40Z

From: Yonghong Song <yhs@fb.com>

[ Upstream commit 528bff0cdb6649f97f2c4802e4ac7a4b50645f2f ]

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 <yhs@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 55bc512a18318..e4e6e2b3fd847 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;
--
2.20.1