Ask for help about bpf map

* Ask for help about bpf map
@ 2021-07-13  6:34 luwei (O)
  2021-07-13 16:16 ` Andrii Nakryiko
  0 siblings, 1 reply; 13+ messages in thread
From: luwei (O) @ 2021-07-13  6:34 UTC (permalink / raw)
  To: bpf

Hi, List:

       I am a beginner about bpf and working on XDP now. I meet a 
problem and feel difficult to figure it out.

       In my following codes, I use two ways to define my_map: in SEC 
maps and SEC .maps respectively. When I load the xdp_kern.o file,

It has different results. The way I load is: ip link set dev ens3 xdp 
obj xdp1_kern.o sec xdp1.

       when I define my_map using SEC maps, it loads successfully but 
fails to load using SEC .maps, it reports:

"

[12] TYPEDEF __u32 type_id=13
[13] INT unsigned int size=4 bits_offset=0 nr_bits=32 encoding=(none)
[14] FUNC_PROTO (anon) return=2 args=(10 ctx)
[15] FUNC xdp_prog1 type_id=14
[16] INT char size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
[17] ARRAY (anon) type_id=16 index_type_id=4 nr_elems=4
[18] VAR _license type_id=17 linkage=1
[19] DATASEC .maps size=0 vlen=1 size == 0

Prog section 'xdp1' rejected: Permission denied (13)!
  - Type:         6
  - Instructions: 9 (0 over limit)
  - License:      GPL

Verifier analysis:

0: (b7) r1 = 0
1: (63) *(u32 *)(r10 -4) = r1
last_idx 1 first_idx 0
regs=2 stack=0 before 0: (b7) r1 = 0
2: (bf) r2 = r10
3: (07) r2 += -4
4: (18) r1 = 0x0
6: (85) call bpf_map_lookup_elem#1
R1 type=inv expected=map_ptr
processed 6 insns (limit 1000000) max_states_per_insn 0 total_states 0 
peak_states 0 mark_read 0

Error fetching program/map!

"

I tried to search google, and only found the following page:

https://stackoverflow.com/questions/67553794/what-is-variable-attribute-sec-means

Does anyone meet the same problem or help to explain this or provide me 
some suggestions ? Thanks !

=== xdp1_kern.c ===

#define KBUILD_MODNAME "foo"
#include <uapi/linux/bpf.h>
#include <linux/time.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <linux/if_vlan.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <bpf/bpf_helpers.h>

struct {
     __uint(type, BPF_MAP_TYPE_HASH);
     __uint(max_entries, 1024);
     __type(key, int);
     __type(value, int);
} my_map SEC(".maps");

#if 0
#define PIN_GLOBAL_NS           2
struct bpf_elf_map {
         __u32 type;
         __u32 size_key;
         __u32 size_value;
         __u32 max_elem;
         __u32 flags;
         __u32 id;
         __u32 pinning;
};

struct bpf_elf_map SEC("maps") my_map = {
         .type = BPF_MAP_TYPE_HASH,
         .size_key = sizeof(int),
         .size_value = sizeof(int),
         .pinning        = PIN_GLOBAL_NS,
         .max_elem = 65535,
};
#endif

SEC("xdp1")
int xdp_prog1(struct xdp_md *ctx)
{
     int key = 0;
     struct map_elem *val;

     val = bpf_map_lookup_elem(&my_map, &key);
     if (val) {
         return XDP_PASS;
     }

     return XDP_PASS;
}

char _license[] SEC("license") = "GPL";

-- 
Best Regards,
Lu Wei

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