* clang-9 and clang-10 BTF miscompilation
@ 2021-03-11 11:23 Lorenz Bauer
2021-03-12 2:33 ` Yonghong Song
0 siblings, 1 reply; 2+ messages in thread
From: Lorenz Bauer @ 2021-03-11 11:23 UTC (permalink / raw)
To: Yonghong Song, Andrii Nakryiko; +Cc: bpf
Hi Yonghong, Andrii,
Given the following C source:
typedef struct {
unsigned char thing[36];
} foo_t;
struct {
__uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS);
__uint(key_size, sizeof(unsigned int));
__uint(max_entries, 1);
__array(
values, struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(max_entries, 1);
__type(key, unsigned int);
__type(value, foo_t);
});
} btf_map __section(".maps");
__section("socket") int filter() {
unsigned int key = 0;
void *value = bpf_map_lookup_elem(&btf_map, (void *)&key);
if (value)
return *(int *)value;
return 0;
}
I get this BTF from clang-9 and clang-10:
[1] STRUCT '(anon)' size=24 vlen=4
'type' type_id=2 bits_offset=0
'key_size' type_id=6 bits_offset=64
'max_entries' type_id=8 bits_offset=128
'values' type_id=16 bits_offset=192
[2] PTR '(anon)' type_id=4
[3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
[4] ARRAY '(anon)' type_id=3 index_type_id=5 nr_elems=12
[5] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none)
[6] PTR '(anon)' type_id=7
[7] ARRAY '(anon)' type_id=3 index_type_id=5 nr_elems=4
[8] PTR '(anon)' type_id=9
[9] ARRAY '(anon)' type_id=3 index_type_id=5 nr_elems=1
[10] PTR '(anon)' type_id=11
[11] STRUCT '(anon)' size=32 vlen=4
'type' type_id=8 bits_offset=0
'max_entries' type_id=8 bits_offset=64
'key' type_id=12 bits_offset=128
'value' type_id=14 bits_offset=192
[12] PTR '(anon)' type_id=13
[13] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none)
[14] PTR '(anon)' type_id=15
[15] TYPEDEF 'foo_t' type_id=1
[16] ARRAY '(anon)' type_id=10 index_type_id=5 nr_elems=0
[17] VAR 'btf_map' type_id=1, linkage=global-alloc
[18] FUNC_PROTO '(anon)' ret_type_id=3 vlen=0
[19] FUNC 'filter' type_id=18
[20] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
[21] ARRAY '(anon)' type_id=20 index_type_id=5 nr_elems=4
[22] VAR '__license' type_id=21, linkage=global-alloc
[23] DATASEC '.maps' size=0 vlen=1
type_id=17 offset=0 size=24
[24] DATASEC 'license' size=0 vlen=1
type_id=22 offset=0 size=4
Note that [15] TYPEDEF 'foo_t' type_id=1 resolves to type 1, which is a
BTF map definition. Clang-11 seems to fix this, so maybe you are already aware.
Best
Lorenz
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: clang-9 and clang-10 BTF miscompilation
2021-03-11 11:23 clang-9 and clang-10 BTF miscompilation Lorenz Bauer
@ 2021-03-12 2:33 ` Yonghong Song
0 siblings, 0 replies; 2+ messages in thread
From: Yonghong Song @ 2021-03-12 2:33 UTC (permalink / raw)
To: Lorenz Bauer, Andrii Nakryiko; +Cc: bpf
On 3/11/21 3:23 AM, Lorenz Bauer wrote:
> Hi Yonghong, Andrii,
>
> Given the following C source:
>
> typedef struct {
> unsigned char thing[36];
> } foo_t;
>
> struct {
> __uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS);
> __uint(key_size, sizeof(unsigned int));
> __uint(max_entries, 1);
> __array(
> values, struct {
> __uint(type, BPF_MAP_TYPE_HASH);
> __uint(max_entries, 1);
> __type(key, unsigned int);
> __type(value, foo_t);
> });
> } btf_map __section(".maps");
>
> __section("socket") int filter() {
> unsigned int key = 0;
> void *value = bpf_map_lookup_elem(&btf_map, (void *)&key);
> if (value)
> return *(int *)value;
> return 0;
> }
>
> I get this BTF from clang-9 and clang-10:
>
> [1] STRUCT '(anon)' size=24 vlen=4
> 'type' type_id=2 bits_offset=0
> 'key_size' type_id=6 bits_offset=64
> 'max_entries' type_id=8 bits_offset=128
> 'values' type_id=16 bits_offset=192
> [2] PTR '(anon)' type_id=4
> [3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
> [4] ARRAY '(anon)' type_id=3 index_type_id=5 nr_elems=12
> [5] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none)
> [6] PTR '(anon)' type_id=7
> [7] ARRAY '(anon)' type_id=3 index_type_id=5 nr_elems=4
> [8] PTR '(anon)' type_id=9
> [9] ARRAY '(anon)' type_id=3 index_type_id=5 nr_elems=1
> [10] PTR '(anon)' type_id=11
> [11] STRUCT '(anon)' size=32 vlen=4
> 'type' type_id=8 bits_offset=0
> 'max_entries' type_id=8 bits_offset=64
> 'key' type_id=12 bits_offset=128
> 'value' type_id=14 bits_offset=192
> [12] PTR '(anon)' type_id=13
> [13] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none)
> [14] PTR '(anon)' type_id=15
> [15] TYPEDEF 'foo_t' type_id=1
The type does not match with code. foo_t here points a map definition
but the code foo_t is used as a value type.
But anyway, I think you mean map definition type is typedef.
Yes, this is fixed in llvm11 by this patch
https://reviews.llvm.org/D83638.
> [16] ARRAY '(anon)' type_id=10 index_type_id=5 nr_elems=0
> [17] VAR 'btf_map' type_id=1, linkage=global-alloc
> [18] FUNC_PROTO '(anon)' ret_type_id=3 vlen=0
> [19] FUNC 'filter' type_id=18
> [20] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
> [21] ARRAY '(anon)' type_id=20 index_type_id=5 nr_elems=4
> [22] VAR '__license' type_id=21, linkage=global-alloc
> [23] DATASEC '.maps' size=0 vlen=1
> type_id=17 offset=0 size=24
> [24] DATASEC 'license' size=0 vlen=1
> type_id=22 offset=0 size=4
>
> Note that [15] TYPEDEF 'foo_t' type_id=1 resolves to type 1, which is a
> BTF map definition. Clang-11 seems to fix this, so maybe you are already aware.
>
> Best
> Lorenz
>
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