From: Rafael David Tinoco <rafaeldtinoco@gmail.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: "Mauricio Vásquez Bernal" <mauricio@kinvolk.io>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Quentin Monnet" <quentin@isovalent.com>,
"Lorenzo Fontana" <lorenzo.fontana@elastic.co>,
"Leonardo Di Donato" <leonardo.didonato@elastic.co>
Subject: Re: [PATCH bpf-next v5 6/9] bpftool: Implement relocations recording for BTFGen
Date: Fri, 4 Feb 2022 03:20:22 -0300 [thread overview]
Message-ID: <8846F5AD-CFD3-4F32-B9C5-E36AB38C37DF@gmail.com> (raw)
In-Reply-To: <CAEf4BzagOBmVbrPOnSwthOxt7CYoqNTuojbtmgskNa_Ad=8EVQ@mail.gmail.com>
>>> As in, do you substitute forward declarations for types that are
>>> never directly used? If not, that's going to be very suboptimal for
>>> something like task_struct and any other type that's part of a big
>>> cluster of types.
>> We decided to include the whole types and all direct and indirect
>> types referenced from a structure field for type-based relocations.
>> Our reasoning is that we don't know if the matching algorithm of
>> libbpf could be changed to require more information in the future and
>> type-based relocations are few compared to field based relocations.
> It will depend on application and which type is used in relocation.
> task_struct reaches tons of types and will add a very noticeable size
> to minimized BTF, for no good reason, IMO. If we discover that we do
> need those types, we'll update bpftool to generate more.
Just to see if I understood this part correctly. IIRC, we started type
based relocations support in btfgen because of this particular case:
union kernfs_node_id {
struct {
u32 ino;
u32 generation;
};
u64 id;
};
struct kernfs_node___older_v55 {
const char *name;
union kernfs_node_id id;
};
struct kernfs_node___rh8 {
const char *name;
union {
u64 id;
struct {
union kernfs_node_id id;
} rh_kabi_hidden_172;
union { };
};
};
So we have 3 situations:
(struct kernfs_node *)->id as u64
[29] STRUCT 'kernfs_node' size=128 vlen=1
'id' type_id=42 bits_offset=832
[42] TYPEDEF 'u64' type_id=10
(struct kernfs_node___older_v55 *)->id as u64 (union kernfs_node_id)->id
[79] STRUCT 'kernfs_node' size=128 vlen=1
'id' type_id=69 bits_offset=832
[69] UNION 'kernfs_node_id' size=8 vlen=2
'(anon)' type_id=132 bits_offset=0
'id' type_id=40 bits_offset=0
[40] TYPEDEF 'u64' type_id=12
(struct kernfs_node___rh8 *)->id = (anon union)->id
[56] STRUCT 'kernfs_node' size=128 vlen=1
'(anon)' type_id=24 bits_offset=832
[24] UNION '(anon)' size=8 vlen=1
'id' type_id=40 bits_offset=0
[40] TYPEDEF 'u64' type_id=11
We're finding needed BTF types, that should be added to generated BTF,
based on fields/members of CORE relo info. How we would know we had to
add the anon union of the last case if it does not exist in the local
BTF ? What is your suggestion ?
Thanks!
-rafaeldtinoco
next prev parent reply other threads:[~2022-02-04 6:20 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-28 22:33 [PATCH bpf-next v5 0/9] libbpf: Implement BTFGen Mauricio Vásquez
2022-01-28 22:33 ` [PATCH bpf-next v5 1/9] libbpf: Implement changes needed for BTFGen in bpftool Mauricio Vásquez
2022-02-01 20:57 ` Quentin Monnet
2022-02-03 16:08 ` Mauricio Vásquez Bernal
2022-02-02 18:54 ` Andrii Nakryiko
2022-02-02 19:02 ` Andrii Nakryiko
2022-02-03 16:09 ` Mauricio Vásquez Bernal
2022-01-28 22:33 ` [PATCH bpf-next v5 2/9] bpftool: Add gen min_core_btf command Mauricio Vásquez
2022-02-02 17:58 ` Andrii Nakryiko
2022-02-03 16:07 ` Mauricio Vásquez Bernal
2022-02-03 17:21 ` Andrii Nakryiko
2022-01-28 22:33 ` [PATCH bpf-next v5 3/9] bpftool: Implement btf_save_raw() Mauricio Vásquez
2022-02-02 18:48 ` Andrii Nakryiko
2022-02-03 16:07 ` Mauricio Vásquez Bernal
2022-02-03 17:23 ` Andrii Nakryiko
2022-01-28 22:33 ` [PATCH bpf-next v5 4/9] bpftool: Add struct definitions and helpers for BTFGen Mauricio Vásquez
2022-02-02 18:54 ` Andrii Nakryiko
2022-02-03 16:08 ` Mauricio Vásquez Bernal
2022-02-03 17:24 ` Andrii Nakryiko
2022-01-28 22:33 ` [PATCH bpf-next v5 5/9] bpftool: Implement btfgen() Mauricio Vásquez
2022-02-01 20:57 ` Quentin Monnet
2022-02-03 19:10 ` Mauricio Vásquez Bernal
2022-02-02 19:14 ` Andrii Nakryiko
2022-02-03 16:09 ` Mauricio Vásquez Bernal
2022-01-28 22:33 ` [PATCH bpf-next v5 6/9] bpftool: Implement relocations recording for BTFGen Mauricio Vásquez
2022-02-02 19:31 ` Andrii Nakryiko
2022-02-03 16:40 ` Mauricio Vásquez Bernal
2022-02-03 17:30 ` Andrii Nakryiko
2022-02-04 6:20 ` Rafael David Tinoco [this message]
2022-02-04 18:41 ` Andrii Nakryiko
2022-02-02 22:55 ` Andrii Nakryiko
2022-02-04 19:44 ` Mauricio Vásquez Bernal
2022-01-28 22:33 ` [PATCH bpf-next v5 7/9] bpftool: Implement btfgen_get_btf() Mauricio Vásquez
2022-02-02 19:36 ` Andrii Nakryiko
2022-02-03 16:10 ` Mauricio Vásquez Bernal
2022-02-03 17:31 ` Andrii Nakryiko
2022-01-28 22:33 ` [PATCH bpf-next v5 8/9] bpftool: gen min_core_btf explanation and examples Mauricio Vásquez
2022-02-01 20:57 ` Quentin Monnet
2022-01-28 22:33 ` [PATCH bpf-next v5 9/9] selftest/bpf: Implement tests for bpftool gen min_core_btf Mauricio Vásquez
2022-01-28 23:23 ` Mauricio Vásquez Bernal
2022-02-01 20:58 ` Quentin Monnet
2022-02-02 19:50 ` Andrii Nakryiko
2022-02-03 21:17 ` Mauricio Vásquez Bernal
2022-02-04 20:05 ` Andrii Nakryiko
2022-02-01 20:57 ` Quentin Monnet
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