Re: [PATCH 1/3] bpf: Move iterator functions into special init section

From: Jiri Olsa <jolsa@redhat.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>, Yonghong Song <yhs@fb.com>,
	Song Liu <songliubraving@fb.com>,
	dwarves@vger.kernel.org, bpf@vger.kernel.org,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andriin@fb.com>, Hao Luo <haoluo@google.com>,
	"Frank Ch. Eigler" <fche@redhat.com>,
	Mark Wielaard <mjw@redhat.com>
Subject: Re: [PATCH 1/3] bpf: Move iterator functions into special init section
Date: Mon, 9 Nov 2020 19:49:30 +0100	[thread overview]
Message-ID: <20201109184930.GA362089@krava> (raw)
In-Reply-To: <20201109180655.GD340169@kernel.org>

On Mon, Nov 09, 2020 at 03:06:55PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Nov 09, 2020 at 03:05:00PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Fri, Nov 06, 2020 at 11:25:10PM +0100, Jiri Olsa escreveu:
> > > With upcoming changes to pahole, that change the way how and
> > > which kernel functions are stored in BTF data, we need a way
> > > to recognize iterator functions.
> > > 
> > > Iterator functions need to be in BTF data, but have no real
> > > body and are currently placed in .init.text section, so they
> > > are freed after kernel init and are filtered out of BTF data
> > > because of that.
> > > 
> > > The solution is to place these functions under new section:
> > >   .init.bpf.preserve_type
> > > 
> > > And add 2 new symbols to mark that area:
> > >   __init_bpf_preserve_type_begin
> > >   __init_bpf_preserve_type_end
> > > 
> > > The code in pahole responsible for picking up the functions will
> > > be able to recognize functions from this section and add them to
> > > the BTF data and filter out all other .init.text functions.
> > 
> > This isn't applying on torvalds/master:
> > 
> > [acme@five linux]$ patch -p1 < /wb/1.patch
> > patching file include/asm-generic/vmlinux.lds.h
> > Hunk #2 succeeded at 754 (offset 1 line).
> > patching file include/linux/bpf.h
> > Hunk #1 succeeded at 1276 (offset -1 lines).
> > patching file include/linux/init.h
> > Hunk #1 FAILED at 52.
> > 1 out of 1 hunk FAILED -- saving rejects to file include/linux/init.h.rej
> > [acme@five linux]$
> > [acme@five linux]$ cat include/linux/init.h.rej
> > --- include/linux/init.h
> > +++ include/linux/init.h
> > @@ -52,6 +52,7 @@
> >  #define __initconst	__section(.init.rodata)
> >  #define __exitdata	__section(.exit.data)
> >  #define __exit_call	__used __section(.exitcall.exit)
> > +#define __init_bpf_preserve_type __section(.init.bpf.preserve_type)
> > 
> >  /*
> >   * modpost check for section mismatches during the kernel build.
> > [acme@five linux]$
> > 
> > 
> > I'm fixing it up by hand to try together with pahole's patches.
> 
> Due to:
> 
> 33def8498fdde180 ("treewide: Convert macro and uses of __section(foo) to __section("foo")")

ok, I'll send new version for the kernel patch

thanks,
jirka