Commit b12d6ec097 ("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: b12d6ec097 ("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>
This consumes functionality exported in the previous patch. It does the
main job of printing with BTF data. This is used in the following patch
to provide a more readable output of a map's dump. It relies on
json_writer to do json printing. Below is sample output where map keys
are ints and values are of type struct A:
typedef int int_type;
enum E {
E0,
E1,
};
struct B {
int x;
int y;
};
struct A {
int m;
unsigned long long n;
char o;
int p[8];
int q[4][8];
enum E r;
void *s;
struct B t;
const int u;
int_type v;
unsigned int w1: 3;
unsigned int w2: 3;
};
$ sudo bpftool map dump id 14
[{
"key": 0,
"value": {
"m": 1,
"n": 2,
"o": "c",
"p": [15,16,17,18,15,16,17,18
],
"q": [[25,26,27,28,25,26,27,28
],[35,36,37,38,35,36,37,38
],[45,46,47,48,45,46,47,48
],[55,56,57,58,55,56,57,58
]
],
"r": 1,
"s": 0x7ffd80531cf8,
"t": {
"x": 5,
"y": 10
},
"u": 100,
"v": 20,
"w1": 0x7,
"w2": 0x3
}
}
]
This patch uses json's {} and [] to imply struct/union and array. More
explicit information can be added later. For example, a command line
option can be introduced to print whether a key or value is struct
or union, name of a struct etc. This will however come at the expense
of duplicating info when, for example, printing an array of structs.
enums are printed as ints without their names.
Signed-off-by: Okash Khawaja <osk@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
