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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 v2 bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section
Date: Thu, 22 Apr 2021 15:56:04 -0700	[thread overview]
Message-ID: <d85c8d5a-7eaf-1d6b-afff-7fddd2083982@fb.com> (raw)
In-Reply-To: <20210416202404.3443623-13-andrii@kernel.org>



On 4/16/21 1:23 PM, 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>

I think strict enforcement of extern/global map definitions is good.
If library want people will use its maps, it may put the map definition
into one of its headers and application can include and have
exact the same definition.

Acked-by: Yonghong Song <yhs@fb.com>

  reply	other threads:[~2021-04-22 22:56 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16 20:23 [PATCH v2 bpf-next 00/17] BPF static linker: support externs Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 01/17] bpftool: support dumping BTF VAR's "extern" linkage Andrii Nakryiko
2021-04-22  3:02   ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 02/17] bpftool: dump more info about DATASEC members Andrii Nakryiko
2021-04-22  3:09   ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 03/17] libbpf: suppress compiler warning when using SEC() macro with externs Andrii Nakryiko
2021-04-22  3:47   ` Yonghong Song
2021-04-22  3:59     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 04/17] libbpf: mark BPF subprogs with hidden visibility as static for BPF verifier Andrii Nakryiko
2021-04-22  5:43   ` Yonghong Song
2021-04-22 18:09     ` Andrii Nakryiko
2021-04-22 23:00       ` Yonghong Song
2021-04-22 23:28         ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 05/17] libbpf: allow gaps in BPF program sections to support overriden weak functions Andrii Nakryiko
2021-04-22  6:25   ` Yonghong Song
2021-04-22 18:10     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 06/17] libbpf: refactor BTF map definition parsing Andrii Nakryiko
2021-04-22 15:33   ` Yonghong Song
2021-04-22 18:40     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 07/17] libbpf: factor out symtab and relos sanity checks Andrii Nakryiko
2021-04-22 16:06   ` Yonghong Song
2021-04-22 18:16     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 08/17] libbpf: make few internal helpers available outside of libbpf.c Andrii Nakryiko
2021-04-22 16:19   ` Yonghong Song
2021-04-22 18:18     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 09/17] libbpf: extend sanity checking ELF symbols with externs validation Andrii Nakryiko
2021-04-22 16:35   ` Yonghong Song
2021-04-22 18:20     ` Andrii Nakryiko
2021-04-22 23:13       ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 10/17] libbpf: tighten BTF type ID rewriting with error checking Andrii Nakryiko
2021-04-22 16:50   ` Yonghong Song
2021-04-22 18:24     ` Andrii Nakryiko
2021-04-23  2:54       ` Alexei Starovoitov
2021-04-23  4:25         ` Andrii Nakryiko
2021-04-23  5:11           ` Alexei Starovoitov
2021-04-23 16:09             ` Andrii Nakryiko
2021-04-23 16:18               ` Alexei Starovoitov
2021-04-23 16:30                 ` Andrii Nakryiko
2021-04-23 16:34                   ` Alexei Starovoitov
2021-04-23 17:02                     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 11/17] libbpf: add linker extern resolution support for functions and global variables Andrii Nakryiko
2021-04-22 21:27   ` Yonghong Song
2021-04-22 22:12     ` Andrii Nakryiko
2021-04-22 23:57       ` Yonghong Song
2021-04-23  2:36         ` Yonghong Song
2021-04-23  4:28           ` Andrii Nakryiko
2021-04-23  4:27         ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section Andrii Nakryiko
2021-04-22 22:56   ` Yonghong Song [this message]
2021-04-22 23:32     ` Andrii Nakryiko
2021-04-16 20:24 ` [PATCH v2 bpf-next 13/17] selftests/bpf: use -O0 instead of -Og in selftests builds Andrii Nakryiko
2021-04-23  0:05   ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 14/17] selftests/bpf: omit skeleton generation for multi-linked BPF object files Andrii Nakryiko
2021-04-23  0:13   ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 15/17] selftests/bpf: add function linking selftest Andrii Nakryiko
2021-04-23  0:50   ` Yonghong Song
2021-04-23  2:34     ` Alexei Starovoitov
2021-04-23  4:29       ` Andrii Nakryiko
2021-04-23 17:18     ` Andrii Nakryiko
2021-04-23 17:35       ` Yonghong Song
2021-04-23 17:55         ` Andrii Nakryiko
2021-04-23 17:58           ` Yonghong Song
2021-04-23 17:59             ` Andrii Nakryiko
2021-04-16 20:24 ` [PATCH v2 bpf-next 16/17] selftests/bpf: add global variables " Andrii Nakryiko
2021-04-23  1:01   ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 17/17] sleftests/bpf: add map " Andrii Nakryiko
2021-04-23  1:20   ` Yonghong Song

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