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Message-ID: <523c1afa-ed9d-4c76-baea-1c43b1b0c682@kernel.org>
Date: Wed, 21 Aug 2024 07:32:21 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Jiri Olsa <olsajiri@...il.com>
Cc: masahiroy@...nel.org, linux-kernel@...r.kernel.org,
Jiri Slaby <jslaby@...e.cz>, Nathan Chancellor <nathan@...nel.org>,
Nicolas Schier <nicolas@...sle.eu>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
<eddyz87@...il.com>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
linux-kbuild@...r.kernel.org, bpf@...r.kernel.org, shung-hsi.yu@...e.com,
msuchanek@...e.com
Subject: Re: [RFC] kbuild: bpf: Do not run pahole with -j on 32bit userspace
On 20. 08. 24, 16:33, Jiri Olsa wrote:
> On Tue, Aug 20, 2024 at 10:59:50AM +0200, Jiri Slaby (SUSE) wrote:
>> From: Jiri Slaby <jslaby@...e.cz>
>>
>> == WARNING ==
>> This is only a PoC. There are deficiencies like CROSS_COMPILE or LLVM
>> are completely unhandled.
>>
>> The simple version is just do there:
>> ifeq ($(CONFIG_64BIT,y)
>> but it has its own deficiencies, of course.
>>
>> So any ideas, inputs?
>> == WARNING ==
>>
>> When pahole is run with -j on 32bit userspace (32bit pahole in
>> particular), it randomly fails with OOM:
>>> btf_encoder__tag_kfuncs: Failed to get ELF section(62) data: out of memory.
>>> btf_encoder__encode: failed to tag kfuncs!
>>
>> or simply SIGSEGV (failed to allocate the btf encoder).
>>
>> It very depends on how many threads are created.
>>
>> So do not invoke pahole with -j on 32bit.
>
> could you share more details about your setup?
>
> does it need to run on pure 32bit to reproduce?
armv7l builds are 32bit only.
> I can't reproduce when
> doing cross build and running 32 bit pahole on x86_64..
i586 is built using 64bit kernel. It is enough to have 32bit userspace.
As written in the linked bug:
https://bugzilla.suse.com/show_bug.cgi?id=1229450#c6
FWIW, steps to reproduce locally:
docker pull jirislaby/pahole_crash
docker run -it jirislaby/pahole_crash
The VM space of pahole is exhausted:
process map: https://bugzilla.suse.com/attachment.cgi?id=876821
strace of mmaps: https://bugzilla.suse.com/attachment.cgi?id=876822
You need to run with large enough -j on a fast machine. Note that this
happens on build hosts even with -j4, but they are under heavy load, so
parallelism of held memory is high.
On my box with 16 cores, it is (likely far) enough to run with -j32.
> I do see some
> errors though
>
> [667939] STRUCT bpf_prog_aux Error emitting BTF type
> Encountered error while encoding BTF.
It's possible that it is one of the errors. There are different ones. As
I wrote above, sometimes it is a crash, sometimes it is the failure I
mentioned above. But it always ends up with a failed build:
> libbpf: failed to find '.BTF' ELF section in vmlinux
> FAILED: load BTF from vmlinux: No data available
> make[2]: *** [../scripts/Makefile.vmlinux:34: vmlinux] Error 255
> make[2]: *** Deleting file 'vmlinux'
> make[1]: ***
[/home/abuild/rpmbuild/BUILD/kernel-vanilla-6.11~rc3.338.gc3f2d783a459/linux-6.11-rc3-338-gc3f2d783a459/Makefile:1158:
vmlinux] Error 2
> make: *** [../Makefile:224: __sub-make] Error 2
> error: Bad exit status from /var/tmp/rpm-tmp.olf5Nu (%build)
thanks,
--
js
suse labs
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