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Date:   Mon, 22 Mar 2021 09:48:43 +0800
From:   Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To:     Yonghong Song <yhs@fb.com>
Cc:     Sami Tolvanen <samitolvanen@google.com>,
        Kees Cook <keescook@chromium.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        <linux-kernel@vger.kernel.org>, <bpf@vger.kernel.org>
Subject: Re: CLANG LTO compatibility issue with DEBUG_INFO_BTF
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On Thu, 18 Mar 2021 20:56:46 -0700 Yonghong Song wrote:


> 
> 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!
> 

Got it. Thanks for the information