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Date:   Mon, 24 Aug 2020 17:43:43 -0700
From:   Yonghong Song <yhs@...com>
To:     Hao Luo <haoluo@...gle.com>
CC:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, Shuah Khan <shuah@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andriin@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Quentin Monnet <quentin@...valent.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Andrey Ignatov <rdna@...com>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [PATCH bpf-next v1 1/8] bpf: Introduce pseudo_btf_id



On 8/24/20 5:05 PM, Hao Luo wrote:
> Yonghong,
> 
> An update on this thread. I successfully reproduced this issue on a
> 8.2.0 gcc compiler, It looks like gcc 4.9 did not have this issue. I
> was also using clang which did not show this bug.
> 
> It seems having a DW_AT_specification that refers to another
> DW_TAG_variable isn't handled in pahole. I have a (maybe hacky) pahole
> patch as fix and let me clean it up and post for review soon.

Sounds good. Thanks for fixing it in pahole! People may use gcc 4.9 up 
to gcc 10, or llvm compiler (let us say llvm10 which is the version 
which has CO-RE support and is recommended for compiling bpf
programs.) Once you have fix for gcc 8.2, it might be worthwhile to
check a few other gcc/llvm version (at least gcc8/9/10 and llvm10)
to ensure it still works.

Currently, by default kernel is using DWARF2, pahole has a good
support for dwarf2. I am not sure whether it supports dwarf4 well
or not. But I think additional dwarf4 support, if needed, can
be done a little bit later as dwarf4 is not widely used yet for kernel,
I think.


> 
> Hao
> 

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