On Wed, Nov 28, 2018 at 09:38:23AM -0800, Yonghong Song wrote:
> 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 <y...@fb.com>
Applied to bpf tree. Thanks
