Re: [PATCH v4 bpf-next 14/22] libbpf: Generate loader program out of BPF ELF file.

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	john fastabend <john.fastabend@gmail.com>,
	bpf <bpf@vger.kernel.org>, Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v4 bpf-next 14/22] libbpf: Generate loader program out of BPF ELF file.
Date: Tue, 11 May 2021 16:22:52 -0700	[thread overview]
Message-ID: <CAEf4BzZzOP6ai0Yf_PbF+At4-UXu0E_8bKyXL4Qj9T6ohxvofQ@mail.gmail.com> (raw)
In-Reply-To: <20210508034837.64585-15-alexei.starovoitov@gmail.com>

On Fri, May 7, 2021 at 8:49 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> From: Alexei Starovoitov <ast@kernel.org>
>
> The BPF program loading process performed by libbpf is quite complex
> and consists of the following steps:
> "open" phase:
> - parse elf file and remember relocations, sections
> - collect externs and ksyms including their btf_ids in prog's BTF
> - patch BTF datasec (since llvm couldn't do it)
> - init maps (old style map_def, BTF based, global data map, kconfig map)
> - collect relocations against progs and maps
> "load" phase:
> - probe kernel features
> - load vmlinux BTF
> - resolve externs (kconfig and ksym)
> - load program BTF
> - init struct_ops
> - create maps
> - apply CO-RE relocations
> - patch ld_imm64 insns with src_reg=PSEUDO_MAP, PSEUDO_MAP_VALUE, PSEUDO_BTF_ID
> - reposition subprograms and adjust call insns
> - sanitize and load progs
>
> During this process libbpf does sys_bpf() calls to load BTF, create maps,
> populate maps and finally load programs.
> Instead of actually doing the syscalls generate a trace of what libbpf
> would have done and represent it as the "loader program".
> The "loader program" consists of single map with:
> - union bpf_attr(s)
> - BTF bytes
> - map value bytes
> - insns bytes
> and single bpf program that passes bpf_attr(s) and data into bpf_sys_bpf() helper.
> Executing such "loader program" via bpf_prog_test_run() command will
> replay the sequence of syscalls that libbpf would have done which will result
> the same maps created and programs loaded as specified in the elf file.
> The "loader program" removes libelf and majority of libbpf dependency from
> program loading process.
>
> kconfig, typeless ksym, struct_ops and CO-RE are not supported yet.
>
> The order of relocate_data and relocate_calls had to change, so that
> bpf_gen__prog_load() can see all relocations for a given program with
> correct insn_idx-es.
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>  tools/lib/bpf/Build              |   2 +-
>  tools/lib/bpf/bpf_gen_internal.h |  40 ++
>  tools/lib/bpf/gen_loader.c       | 657 +++++++++++++++++++++++++++++++
>  tools/lib/bpf/libbpf.c           | 224 +++++++++--
>  tools/lib/bpf/libbpf.h           |  12 +
>  tools/lib/bpf/libbpf.map         |   1 +
>  tools/lib/bpf/libbpf_internal.h  |   2 +
>  tools/lib/bpf/skel_internal.h    | 116 ++++++
>  8 files changed, 1022 insertions(+), 32 deletions(-)
>  create mode 100644 tools/lib/bpf/bpf_gen_internal.h
>  create mode 100644 tools/lib/bpf/gen_loader.c
>  create mode 100644 tools/lib/bpf/skel_internal.h
>

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