netdev - Re: [PATCH bpf-next v3 0/8] bpf: btf: fix struct/union/fwd types with kind

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Message-ID: <635d452c-115d-6777-ff3f-180d448dcee8@iogearbox.net>
Date:   Tue, 18 Dec 2018 01:18:05 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Yonghong Song <yhs@...com>, netdev@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...com>, kernel-team@...com,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf-next v3 0/8] bpf: btf: fix struct/union/fwd types with
 kind_flag

On 12/16/2018 07:13 AM, Yonghong Song wrote:
> Commit 69b693f0aefa ("bpf: btf: Introduce BPF Type Format (BTF)")
> introduced BTF, a debug info format for BTF.
> 
> The original design has a couple of issues though.
> First, the bitfield size is only encoded in int type.
> If the struct member bitfield type is enum, pahole ([1])
> or llvm is forced to replace enum with int type. As a result, the original
> type information gets lost.
> 
> Second, the original BTF design does not envision the possibility of
> BTF=>header_file conversion ([2]), hence does not encode "struct" or
> "union" info for a forward type. Such information is necessary to
> convert BTF to a header file.
> 
> This patch set fixed the issue by introducing kind_flag, using one bit
> in type->info. When kind_flag, the struct/union btf_member->offset
> will encode both bitfield_size and bit_offset, covering both
> int and enum base types. The kind_flag is also used to indicate whether
> the forward type is a union (when set) or a struct.
> 
> Patch #1 refactors function btf_int_bits_seq_show() so Patch #2
> can reuse part of the function.
> Patch #2 implemented kind_flag support for struct/union/fwd types.
> Patch #3 added kind_flag support for cgroup local storage map pretty print.
> Patch #4 syncs kernel uapi btf.h to tools directory.
> Patch #5 added unit tests for kind_flag.
> Patch #6 added tests for kernel bpffs based pretty print with kind_flag.
> Patch #7 refactors function btf_dumper_int_bits() so Patch #8
> can reuse part of the function.
> Patch #8 added bpftool support of pretty print with kind_flag set.
> 
> [1] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?id=b18354f64cc215368c3bc0df4a7e5341c55c378c
> [2] https://lwn.net/SubscriberLink/773198/fe3074838f5c3f26/
> 
> Change logs:
>   v2 -> v3:
>     . Relocated comments about bitfield_size/bit_offset interpretation
>       of the "offset" field right before the "offset" struct member.
>     . Added missing byte alignment checking for non-bitfield enum
>       member of a struct with kind_flag set.
>     . Added two test cases in unit tests for struct type, kind_flag set,
>       non-bitfield int/enum member, not-byte aligned bit offsets.
>     . Added comments to help understand there is no overflow for
>       total_bits_offset in bpftool function btf_dumper_int_bits().
>     . Added explanation of typedef type dumping fix in Patch #8 commit
>       message.
> 
>   v1 -> v2:
>     . If kind_flag is set for a structure, ensure an int member,
>       whether it is a bitfield or not, is a regular int type.
>     . Added support so cgroup local storage map pretty print
>       works with kind_flag.
> 
> Yonghong Song (8):
>   bpf: btf: refactor btf_int_bits_seq_show()
>   bpf: btf: fix struct/union/fwd types with kind_flag
>   bpf: enable cgroup local storage map pretty print with kind_flag
>   tools/bpf: sync btf.h header from kernel to tools
>   tools/bpf: add test_btf unit tests for kind_flag
>   tools/bpf: test kernel bpffs map pretty print with struct kind_flag
>   tools: bpftool: refactor btf_dumper_int_bits()
>   tools: bpftool: support pretty print with kind_flag set
> 
>  include/linux/btf.h                    |   5 +-
>  include/uapi/linux/btf.h               |  20 +-
>  kernel/bpf/btf.c                       | 352 +++++++++++--
>  kernel/bpf/local_storage.c             |  17 +-
>  tools/bpf/bpftool/btf_dumper.c         |  61 ++-
>  tools/include/uapi/linux/btf.h         |  20 +-
>  tools/testing/selftests/bpf/test_btf.c | 664 ++++++++++++++++++++++++-
>  7 files changed, 1047 insertions(+), 92 deletions(-)
> 

Applied to bpf-next, thanks!