From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
Networking <netdev@vger.kernel.org>,
Alexei Starovoitov <ast@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Yonghong Song <yhs@fb.com>, Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v4 bpf-next 02/14] libbpf: convert libbpf code to use new btf helpers
Date: Wed, 7 Aug 2019 12:59:53 -0700 [thread overview]
Message-ID: <CAEf4BzahxLWRVNcNWpba7_7CbbQgN8k0RU8Ya1XCK8j4rPQ0NQ@mail.gmail.com> (raw)
In-Reply-To: <20190807193011.g2zuaapc2uvvr4h6@ast-mbp>
On Wed, Aug 7, 2019 at 12:30 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Tue, Aug 06, 2019 at 10:37:54PM -0700, Andrii Nakryiko wrote:
> > Simplify code by relying on newly added BTF helper functions.
> >
> > Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> ..
> >
> > - for (i = 0, vsi = (struct btf_var_secinfo *)(t + 1);
> > - i < vars; i++, vsi++) {
> > + for (i = 0, vsi = (void *)btf_var_secinfos(t); i < vars; i++, vsi++) {
>
> > + struct btf_member *m = (void *)btf_members(t);
> ...
> > case BTF_KIND_ENUM: {
> > - struct btf_enum *m = (struct btf_enum *)(t + 1);
> > - __u16 vlen = BTF_INFO_VLEN(t->info);
> > + struct btf_enum *m = (void *)btf_enum(t);
> > + __u16 vlen = btf_vlen(t);
> ...
> > case BTF_KIND_FUNC_PROTO: {
> > - struct btf_param *m = (struct btf_param *)(t + 1);
> > - __u16 vlen = BTF_INFO_VLEN(t->info);
> > + struct btf_param *m = (void *)btf_params(t);
> > + __u16 vlen = btf_vlen(t);
>
> So all of these 'void *' type hacks are only to drop const-ness ?
Yes.
> May be the helpers shouldn't be taking const then?
>
Probably not, because then we'll have much wider-spread problem of
casting const pointers into non-const when passing btf_type into
helpers.
I think const as a default is the right choice, because normally BTF
is immutable and btf__type_by_id is returning const pointer, etc.
That's typical and expected use-case. btf_dedup and BTF sanitization +
datasec size setting pieces are an exception that have to modify BTF
types in place before passing it to user.
So realistically I think we can just leave it as (void *), or I can do
explicit non-const type casts, or we can just not use helpers for
mutable cases. Do you have a preference?
next prev parent reply other threads:[~2019-08-07 20:00 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-07 5:37 [PATCH v4 bpf-next 00/14] CO-RE offset relocations Andrii Nakryiko
2019-08-07 5:37 ` [PATCH v4 bpf-next 01/14] libbpf: add helpers for working with BTF types Andrii Nakryiko
2019-08-07 19:31 ` Alexei Starovoitov
2019-08-07 19:54 ` Andrii Nakryiko
2019-08-07 5:37 ` [PATCH v4 bpf-next 02/14] libbpf: convert libbpf code to use new btf helpers Andrii Nakryiko
2019-08-07 19:30 ` Alexei Starovoitov
2019-08-07 19:59 ` Andrii Nakryiko [this message]
2019-08-07 20:01 ` Alexei Starovoitov
2019-08-07 20:10 ` Andrii Nakryiko
2019-08-07 5:37 ` [PATCH v4 bpf-next 03/14] libbpf: add .BTF.ext offset relocation section loading Andrii Nakryiko
2019-08-07 5:37 ` [PATCH v4 bpf-next 04/14] libbpf: implement BPF CO-RE offset relocation algorithm Andrii Nakryiko
2019-08-07 5:37 ` [PATCH v4 bpf-next 05/14] selftests/bpf: add BPF_CORE_READ relocatable read macro Andrii Nakryiko
2019-08-07 5:37 ` [PATCH v4 bpf-next 06/14] selftests/bpf: add CO-RE relocs testing setup Andrii Nakryiko
2019-08-07 5:37 ` [PATCH v4 bpf-next 07/14] selftests/bpf: add CO-RE relocs struct flavors tests Andrii Nakryiko
2019-08-07 5:38 ` [PATCH v4 bpf-next 08/14] selftests/bpf: add CO-RE relocs nesting tests Andrii Nakryiko
2019-08-07 5:38 ` [PATCH v4 bpf-next 09/14] selftests/bpf: add CO-RE relocs array tests Andrii Nakryiko
2019-08-07 5:38 ` [PATCH v4 bpf-next 10/14] selftests/bpf: add CO-RE relocs enum/ptr/func_proto tests Andrii Nakryiko
2019-08-07 5:38 ` [PATCH v4 bpf-next 11/14] selftests/bpf: add CO-RE relocs modifiers/typedef tests Andrii Nakryiko
2019-08-07 5:38 ` [PATCH v4 bpf-next 12/14] selftests/bpf: add CO-RE relocs ptr-as-array tests Andrii Nakryiko
2019-08-07 5:38 ` [PATCH v4 bpf-next 13/14] selftests/bpf: add CO-RE relocs ints tests Andrii Nakryiko
2019-08-07 5:38 ` [PATCH v4 bpf-next 14/14] selftests/bpf: add CO-RE relocs misc tests Andrii Nakryiko
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