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Date:   Fri, 19 Mar 2021 11:45:44 +0800
From:   Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To:     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
Cc:     bpf@vger.kernel.org
Subject: CLANG LTO compatibility issue with DEBUG_INFO_BTF
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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?

pahole version: v1.20
clang version: 11.0


Thanks