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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

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")")

I'm using this now:

diff --git a/include/linux/init.h b/include/linux/init.h
index 7b53cb3092ee9956..a7c71e3b5f9a1d65 100644
--- a/include/linux/init.h
+++ b/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.