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Message-ID: <4e1d1504-55e5-db8b-112b-921d86ef7d5b@fb.com>
Date: Thu, 18 Mar 2021 20:56:46 -0700
From: Yonghong Song <yhs@...com>
To: Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Kees Cook <keescook@...omium.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
<linux-kernel@...r.kernel.org>
CC: <bpf@...r.kernel.org>
Subject: Re: CLANG LTO compatibility issue with DEBUG_INFO_BTF
On 3/18/21 8:45 PM, Jisheng Zhang wrote:
> Hi,
>
> When trying the latest 5.12-rc3 with both LTO_CLANG_THIN and DEBUG_INFO_BTF
> enabled, I met lots of warnings such as:
>
> ...
> tag__recode_dwarf_type: couldn't find 0x4a7ade5 type for 0x4ab9f88 (subroutine_type)!
> ftype__recode_dwarf_types: couldn't find 0x4a7ade5 type for 0x4ab9fa4 (formal_parameter)!
> ...
> namespace__recode_dwarf_types: couldn't find 0x4a8ff4a type for 0x4aba05c (member)!
> namespace__recode_dwarf_types: couldn't find 0x4a7ae9b type for 0x4aba084 (member)!
> ...
> WARN: multiple IDs found for 'path': 281, 729994 - using 281
> WARN: multiple IDs found for 'task_struct': 421, 730101 - using 421
> ...
>
>
> then finally get build error:
> FAILED unresolved symbol vfs_truncate
>
>
> Is this a known issue? Do we need to make DEBUG_INFO_BTF depend on !LTO?
This is a known issue for pahole. pahole does not handle dwarf well
generated with LTO. Bill Wendling from google is looking at the issue
and I will help look at the issue as well. Since bpf heavily depends
on BTF, at this point, I suggest if you are using bpf, please do not
turn on LTO. Or if you build with LTO, just turn off DEBUG_INFO_BTF
in your config. Thanks!
>
> pahole version: v1.20
> clang version: 11.0
>
>
> Thanks
>
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