From: Yonghong Song <yhs@fb.com>
To: Andrii Nakryiko <andrii@kernel.org>, <bpf@vger.kernel.org>,
<netdev@vger.kernel.org>, <ast@fb.com>, <daniel@iogearbox.net>
Cc: <kernel-team@fb.com>
Subject: Re: [PATCH v3 bpf-next 12/18] libbpf: support extern resolution for BTF-defined maps in .maps section
Date: Fri, 23 Apr 2021 11:49:15 -0700 [thread overview]
Message-ID: <df3be1a8-a8b7-b79a-2264-b5ccb2d5a105@fb.com> (raw)
In-Reply-To: <20210423181348.1801389-13-andrii@kernel.org>
On 4/23/21 11:13 AM, Andrii Nakryiko wrote:
> Add extra logic to handle map externs (only BTF-defined maps are supported for
> linking). Re-use the map parsing logic used during bpf_object__open(). Map
> externs are currently restricted to always match complete map definition. So
> all the specified attributes will be compared (down to pining, map_flags,
> numa_node, etc). In the future this restriction might be relaxed with no
> backwards compatibility issues. If any attribute is mismatched between extern
> and actual map definition, linker will report an error, pointing out which one
> mismatches.
>
> The original intent was to allow for extern to specify attributes that matters
> (to user) to enforce. E.g., if you specify just key information and omit
> value, then any value fits. Similarly, it should have been possible to enforce
> map_flags, pinning, and any other possible map attribute. Unfortunately, that
> means that multiple externs can be only partially overlapping with each other,
> which means linker would need to combine their type definitions to end up with
> the most restrictive and fullest map definition. This requires an extra amount
> of BTF manipulation which at this time was deemed unnecessary and would
> require further extending generic BTF writer APIs. So that is left for future
> follow ups, if there will be demand for that. But the idea seems intresting
> and useful, so I want to document it here.
>
> Weak definitions are also supported, but are pretty strict as well, just
> like externs: all weak map definitions have to match exactly. In the follow up
> patches this most probably will be relaxed, with __weak map definitions being
> able to differ between each other (with non-weak definition always winning, of
> course).
>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
next prev parent reply other threads:[~2021-04-23 18:49 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-23 18:13 [PATCH v3 bpf-next 00/18] BPF static linker: support externs Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 01/18] bpftool: support dumping BTF VAR's "extern" linkage Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 02/18] bpftool: dump more info about DATASEC members Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 03/18] libbpf: suppress compiler warning when using SEC() macro with externs Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 04/18] libbpf: mark BPF subprogs with hidden visibility as static for BPF verifier Andrii Nakryiko
2021-04-23 18:23 ` Yonghong Song
2021-04-23 18:13 ` [PATCH v3 bpf-next 05/18] libbpf: allow gaps in BPF program sections to support overriden weak functions Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 06/18] libbpf: refactor BTF map definition parsing Andrii Nakryiko
2021-04-23 18:36 ` Yonghong Song
2021-04-23 18:13 ` [PATCH v3 bpf-next 07/18] libbpf: factor out symtab and relos sanity checks Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 08/18] libbpf: make few internal helpers available outside of libbpf.c Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 09/18] libbpf: extend sanity checking ELF symbols with externs validation Andrii Nakryiko
2021-04-23 18:39 ` Yonghong Song
2021-04-23 18:13 ` [PATCH v3 bpf-next 10/18] libbpf: tighten BTF type ID rewriting with error checking Andrii Nakryiko
2021-04-23 18:40 ` Yonghong Song
2021-04-23 18:13 ` [PATCH v3 bpf-next 11/18] libbpf: add linker extern resolution support for functions and global variables Andrii Nakryiko
2021-04-23 18:46 ` Yonghong Song
2021-04-23 18:13 ` [PATCH v3 bpf-next 12/18] libbpf: support extern resolution for BTF-defined maps in .maps section Andrii Nakryiko
2021-04-23 18:49 ` Yonghong Song [this message]
2021-04-23 18:13 ` [PATCH v3 bpf-next 13/18] selftests/bpf: use -O0 instead of -Og in selftests builds Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 14/18] selftests/bpf: omit skeleton generation for multi-linked BPF object files Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 15/18] selftests/bpf: add function linking selftest Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 16/18] selftests/bpf: add global variables " Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 17/18] selftests/bpf: add map " Andrii Nakryiko
2021-04-23 18:53 ` Yonghong Song
2021-04-23 21:23 ` Alexei Starovoitov
2021-04-23 21:39 ` Andrii Nakryiko
2021-04-23 18:13 ` [PATCH v3 bpf-next 18/18] selftests/bpf: document latest Clang fix expectations for linking tests Andrii Nakryiko
2021-04-23 18:51 ` Yonghong Song
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