From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Martin Lau <kafai@fb.com>
Cc: Yonghong Song <yhs@fb.com>,
"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
David Miller <davem@davemloft.net>,
Kernel Team <Kernel-team@fb.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next 06/13] bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS
Date: Fri, 20 Dec 2019 10:41:20 -0800 [thread overview]
Message-ID: <CAEf4BzZDSaw18f3je0=+kG38F0+3G1zcB48T_He2H5LhJQ3ygg@mail.gmail.com> (raw)
In-Reply-To: <20191220165158.bc6mp7w5ooof262h@kafai-mbp>
On Fri, Dec 20, 2019 at 8:52 AM Martin Lau <kafai@fb.com> wrote:
>
> On Thu, Dec 19, 2019 at 11:22:17PM -0800, Martin Lau wrote:
>
> > [ ... ]
> >
> > > > +/* __bpf_##_name (e.g. __bpf_tcp_congestion_ops) is the map's value
> > > > + * exposed to the userspace and its btf-type-id is stored
> > > > + * at the map->btf_vmlinux_value_type_id.
> > > > + *
> > > > + * The *_name##_dummy is to ensure the BTF type is emitted.
> > > > + */
> > > > +
> > > > #define BPF_STRUCT_OPS_TYPE(_name) \
> > > > -extern struct bpf_struct_ops bpf_##_name;
> > > > +extern struct bpf_struct_ops bpf_##_name; \
> > > > + \
> > > > +static struct __bpf_##_name { \
> > > > + BPF_STRUCT_OPS_COMMON_VALUE; \
> > > > + struct _name data ____cacheline_aligned_in_smp; \
> > > > +} *_name##_dummy;
> > >
> > > There are other ways to retain types in debug info without
> > > creating new variables. For example, you can use it in a cast
> > > like
> > > (void *)(struct __bpf_##_name *)v
> > hmm... What is v?
> Got it. "v" could be any dummy pointer in a function.
> I will use (void) instead of (void *) to avoid compiler warning.
>
This discussion inspired me to try this:
#define PRESERVE_TYPE_INFO(type) ((void)(type *)0)
... somewhere in any function ...
PRESERVE_TYPE_INFO(struct whatever_struct);
And it works! We should probably put this helper macro somewhere in
include/linux/bpf.h and use it consistently for cases like this.
> >
> > > Not sure whether we could easily find a place for such casting or not.
> This can be done in bpf_struct_ops_init().
>
> Thanks for the tips!
next prev parent reply other threads:[~2019-12-20 18:41 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-14 0:47 [PATCH bpf-next 00/13] Introduce BPF STRUCT_OPS Martin KaFai Lau
2019-12-14 0:47 ` [PATCH bpf-next 01/13] bpf: Save PTR_TO_BTF_ID register state when spilling to stack Martin KaFai Lau
2019-12-16 19:48 ` Yonghong Song
2019-12-14 0:47 ` [PATCH bpf-next 02/13] bpf: Avoid storing modifier to info->btf_id Martin KaFai Lau
2019-12-16 21:34 ` Yonghong Song
2019-12-14 0:47 ` [PATCH bpf-next 03/13] bpf: Add enum support to btf_ctx_access() Martin KaFai Lau
2019-12-16 21:36 ` Yonghong Song
2019-12-14 0:47 ` [PATCH bpf-next 04/13] bpf: Support bitfield read access in btf_struct_access Martin KaFai Lau
2019-12-16 22:05 ` Yonghong Song
2019-12-14 0:47 ` [PATCH bpf-next 05/13] bpf: Introduce BPF_PROG_TYPE_STRUCT_OPS Martin KaFai Lau
2019-12-17 6:14 ` Yonghong Song
2019-12-18 16:41 ` Martin Lau
2019-12-14 0:47 ` [PATCH bpf-next 06/13] bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS Martin KaFai Lau
2019-12-17 7:48 ` [Potential Spoof] " Yonghong Song
2019-12-20 7:22 ` Martin Lau
2019-12-20 16:52 ` Martin Lau
2019-12-20 18:41 ` Andrii Nakryiko [this message]
2019-12-14 0:47 ` [PATCH bpf-next 07/13] bpf: tcp: Support tcp_congestion_ops in bpf Martin KaFai Lau
2019-12-17 17:36 ` Yonghong Song
2019-12-14 0:47 ` [PATCH bpf-next 08/13] bpf: Add BPF_FUNC_tcp_send_ack helper Martin KaFai Lau
2019-12-17 17:41 ` Yonghong Song
2019-12-14 0:47 ` [PATCH bpf-next 09/13] bpf: Add BPF_FUNC_jiffies Martin KaFai Lau
2019-12-14 1:59 ` Eric Dumazet
2019-12-14 19:25 ` Neal Cardwell
2019-12-16 19:30 ` Martin Lau
2019-12-17 8:26 ` Jakub Sitnicki
2019-12-17 18:22 ` Martin Lau
2019-12-17 21:04 ` Eric Dumazet
2019-12-18 9:03 ` Jakub Sitnicki
2019-12-16 19:14 ` Martin Lau
2019-12-16 19:33 ` Eric Dumazet
2019-12-16 21:17 ` Martin Lau
2019-12-16 23:08 ` Alexei Starovoitov
2019-12-17 0:34 ` Eric Dumazet
2019-12-14 0:48 ` [PATCH bpf-next 10/13] bpf: Synch uapi bpf.h to tools/ Martin KaFai Lau
2019-12-14 0:48 ` [PATCH bpf-next 11/13] bpf: libbpf: Add STRUCT_OPS support Martin KaFai Lau
2019-12-18 3:07 ` Andrii Nakryiko
2019-12-18 7:03 ` Martin Lau
2019-12-18 7:20 ` Martin Lau
2019-12-18 16:36 ` Andrii Nakryiko
2019-12-18 16:34 ` Andrii Nakryiko
2019-12-18 17:33 ` Martin Lau
2019-12-18 18:14 ` Andrii Nakryiko
2019-12-18 20:19 ` Martin Lau
2019-12-19 8:53 ` Toke Høiland-Jørgensen
2019-12-19 20:49 ` Andrii Nakryiko
2019-12-20 10:16 ` Toke Høiland-Jørgensen
2019-12-20 17:34 ` Andrii Nakryiko
2019-12-14 0:48 ` [PATCH bpf-next 12/13] bpf: Add bpf_dctcp example Martin KaFai Lau
2019-12-14 0:48 ` [PATCH bpf-next 13/13] bpf: Add bpf_cubic example Martin KaFai Lau
2019-12-14 2:26 ` [PATCH bpf-next 00/13] Introduce BPF STRUCT_OPS Eric Dumazet
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