linux-kernel - Re: linux-next failing build due to missing cubictcp

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Date:   Mon, 3 May 2021 10:59:44 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Michal Suchánek <msuchanek@...e.de>,
        Jiri Olsa <jolsa@...hat.com>
Cc:     Yonghong Song <yhs@...com>, linux-kernel@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        dwarves@...r.kernel.org, Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: linux-next failing build due to missing cubictcp_state symbol

CCing pahole people.

On 03. 05. 21, 9:59, Jiri Slaby wrote:
> On 03. 05. 21, 8:11, Jiri Slaby wrote:
>>>>>>> looks like vfs_truncate did not get into BTF data,
>>>>>>> I'll try to reproduce
>>>
>>> _None_ of the functions are generated by pahole -J from debuginfo on 
>>> ppc64. debuginfo appears to be correct. Neither pahole -J fs/open.o 
>>> works correctly. collect_functions in dwarves seems to be defunct on 
>>> ppc64... "functions" array is bogus (so find_function -- the bsearch 
>>> -- fails).
>>
>> It's not that bogus. I forgot an asterisk:
>>> #0  find_function (btfe=0x100269f80, name=0x10024631c "stream_open") 
>>> at /usr/src/debug/dwarves-1.21-1.1.ppc64/btf_encoder.c:350
>>> (gdb) p (*functions)@84
>>> $5 = {{name = 0x7ffff68e0922 ".__se_compat_sys_ftruncate", addr = 
>>> 75232, size = 72, sh_addr = 65536, generated = false}, {
>>>     name = 0x7ffff68e019e ".__se_compat_sys_open", addr = 80592, size 
>>> = 216, sh_addr = 65536, generated = false}, {
>>>     name = 0x7ffff68e0076 ".__se_compat_sys_openat", addr = 80816, 
>>> size = 232, sh_addr = 65536, generated = false}, {
>>>     name = 0x7ffff68e0908 ".__se_compat_sys_truncate", addr = 74304, 
>>> size = 100, sh_addr = 65536, generated = false}, {
>> ...
>>>     name = 0x7ffff68e0808 ".stream_open", addr = 65824, size = 72, 
>>> sh_addr = 65536, generated = false}, {
>> ...
>>>     name = 0x7ffff68e0751 ".vfs_truncate", addr = 73392, size = 544, 
>>> sh_addr = 65536, generated = false}}
>>
>> The dot makes the difference, of course. The question is why is it 
>> there? I keep looking into it. Only if someone has an immediate idea...
> 
> Well, .vfs_truncate is in .text (and contains an ._mcount call). And 
> vfs_truncate is in .opd (w/o an ._mcount call). Since setup_functions 
> excludes all functions without the ._mcount call, is_ftrace_func later 
> returns false for such functions and they are filtered before the BTF 
> processing.
> 
> Technically, get_vmlinux_addrs looks at a list of functions between 
> __start_mcount_loc and __stop_mcount_loc and considers only the listed.
> 
> I don't know what the correct fix is (exclude .opd functions from the 
> filter?). Neither why cross compiler doesn't fail, nor why ebi v2 avoids 
> this too.

Attaching a patch for pahole which fixes the issue, but I have no idea 
whether it is the right fix at all.

> regards,-- 
js
suse labs

View attachment "ppc64-opd-fix.patch" of type "text/x-patch" (1687 bytes)