Re: [PATCH v2] pahole: Add --kabi_prefix flag

From: Jiri Olsa <jolsa@redhat.com>
To: Shuyi Cheng <chengshuyi@linux.alibaba.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
	dwarves@vger.kernel.org, wenan.mao@linux.alibaba.com,
	Jiri Olsa <jolsa@kernel.org>
Subject: Re: [PATCH v2] pahole: Add --kabi_prefix flag
Date: Thu, 20 May 2021 14:18:21 +0200	[thread overview]
Message-ID: <YKZTjViH1uJoMSyI@krava> (raw)
In-Reply-To: <ebbd7ace-f3ab-d104-c36c-788f4c169bbd@linux.alibaba.com>

On Thu, May 20, 2021 at 08:08:44PM +0800, Shuyi Cheng wrote:
> 
> 
> On 5/20/21 7:49 PM, Jiri Olsa wrote:
> > On Thu, May 20, 2021 at 06:27:48PM +0800, Shuyi Cheng wrote:
> > > 
> > > 
> > > On 5/20/21 4:07 AM, Jiri Olsa wrote:
> > > > On Wed, May 19, 2021 at 10:44:44AM +0800, Shuyi Cheng wrote:
> > > > > To solve problems similar to _RH_KABI_REPLACE. The _RH_KABI_REPLACE(_orig,
> > > > > _new) macros perserve size alignment and kabi agreement between _orig and
> > > > > _new.Below is the definition of this macro:
> > > > > 
> > > > > # define _RH_KABI_REPLACE(_orig, _new)            \
> > > > >       union {                        \
> > > > >           _new;                    \
> > > > >           struct {                \
> > > > >               _orig;                \
> > > > >           } __UNIQUE_ID(rh_kabi_hide);        \
> > > > >           __RH_KABI_CHECK_SIZE_ALIGN(_orig, _new);    \
> > > > >       }
> > > > 
> > > > hi,
> > > > that macro sounds familiar ;-) I think this should be already
> > > > solved directly in the header file by this one:
> > > > 
> > > >     https://gitlab.com/cki-project/kernel-ark/-/commit/331be9c5a436057ee852075c102d9d90a9046a30
> > > > 
> > > > jirka
> > > > 
> > > 
> > > Well, this patch solves this problem very well from the kernel level. But
> > > there are many mirrors [here](http://debuginfo.centos.org/7/x86_64/) that
> > > still have this problem. And these mirrors support ebpf, so it is very
> > > important to effectively extract the btf segment from these mirrors. :-)
> > 
> > hum, the link shows 3.10.* centos kernel, right?
> > AFAIK there's no BTF support in those kernels..
> > 
> > but maybe I'm missing some backporting channel,
> > could you please point me to related sources?
> > 
> > jirka
> > 
> 
> Yes, it is the centos kernel of version 3.10. This version of the centos
> kernel supports ebpf. As far as I think, BTF features don't depend on the
> kernel much. Only when using the STRUCT OPS feature does the kernel support
> BTF, see [here](https://github.com/libbpf/libbpf/blob/57375504c6c9766d23f178c40f71bf5e8df9363d/src/libbpf.c#L2549)
> and [here](https://www.spinics.net/lists/netdev/msg637060.html). Therefore,
> in the 3.10 version of the Centos kernel, with the help of the vmlinux btf
> segment, libbpf CO-RE can be easily supported.

ok, so you're generating BTF for centos 3.10 kernel?

I think that fix would be easy kernel backport, but I guess
we can go with pahole option just as well, if backport is
not an option for you

jirka