Re: [PATCH] ebpf: fix compatibility with libbpf 1.0+

[Shreesh Adiga]

On Sun, Dec 18, 2022 at 05:15:04PM +0100, Philippe Mathieu-Daudé wrote:
> Hi,
>
> On 18/12/22 15:39, Shreesh Adiga wrote:
> > The current implementation fails to load on a system with
> > libbpf 1.0 and reports that legacy map definitions in 'maps'
> > section are not supported by libbpf v1.0+. This commit updates
> > the Makefile to add BTF (-g flag) and appropriately updates
> > the maps in rss.bpf.c and update the skeleton file in repo.
> >
> > Signed-off-by: Shreesh Adiga <16567adigashreesh@gmail.com>
> > ---
> >   ebpf/rss.bpf.skeleton.h  | 1171 ++++++++++++++++++++++++++++----------
> >   tools/ebpf/Makefile.ebpf |    8 +-
> >   tools/ebpf/rss.bpf.c     |   43 +-
> >   3 files changed, 891 insertions(+), 331 deletions(-)
>
>
> > +static inline const void *rss_bpf__elf_bytes(size_t *sz)
> > +{
> > +   *sz = 20440;
> > +   return (const void *)"\
> >   
> > \x7f\x45\x4c\x46\x02\x01\x01\0\0\0\0\0\0\0\0\0\x01\0\xf7\0\x01\0\0\0\0\0\0\0\0\
> > -\0\0\0\0\0\0\0\0\0\0\0\x18\x1d\0\0\0\0\0\0\0\0\0\0\x40\0\0\0\0\0\x40\0\x0a\0\
> > -\x01\0\xbf\x18\0\0\0\0\0\0\xb7\x01\0\0\0\0\0\0\x63\x1a\x4c\xff\0\0\0\0\xbf\xa7\
> > -\0\0\0\0\0\0\x07\x07\0\0\x4c\xff\xff\xff\x18\x01\0\0\0\0\0\0\0\0\0\0\0\0\0\0\
> > +\0\0\0\0\0\0\0\0\0\0\0\x98\x4c\0\0\0\0\0\0\0\0\0\0\x40\0\0\0\0\0\x40\0\x0d\0\
> > +\x01\0\xbf\x19\0\0\0\0\0\0\xb7\x01\0\0\0\0\0\0\x63\x1a\x54\xff\0\0\0\0\xbf\xa7\
> > +\0\0\0\0\0\0\x07\x07\0\0\x54\xff\xff\xff\x18\x01\0\0\0\0\0\0\0\0\0\0\0\0\0\0\
> >   
> > \xbf\x72\0\0\0\0\0\0\x85\0\0\0\x01\0\0\0\xbf\x06\0\0\0\0\0\0\x18\x01\0\0\0\0\0\
> > -\0\0\0\0\0\0\0\0\0\xbf\x72\0\0\0\0\0\0\x85\0\0\0\x01\0\0\0\xbf\x07\0\0\0\0\0\0\
> > -\x18\0\0\0\xff\xff\xff\xff\0\0\0\0\0\0\0\0\x15\x06\x66\x02\0\0\0\0\xbf\x79\0\0\
> > -\0\0\0\0\x15\x09\x64\x02\0\0\0\0\x71\x61\0\0\0\0\0\0\x55\x01\x01\0\0\0\0\0\x05\
> > -\0\x5d\x02\0\0\0\0\xb7\x01\0\0\0\0\0\0\x63\x1a\xc0\xff\0\0\0\0\x7b\x1a\xb8\xff\
> > -\0\0\0\0\x7b\x1a\xb0\xff\0\0\0\0\x7b\x1a\xa8\xff\0\0\0\0\x7b\x1a\xa0\xff\0\0\0\
> > -\0\x63\x1a\x98\xff\0\0\0\0\x7b\x1a\x90\xff\0\0\0\0\x7b\x1a\x88\xff\0\0\0\0\x7b\
> > -\x1a\x80\xff\0\0\0\0\x7b\x1a\x78\xff\0\0\0\0\x7b\x1a\x70\xff\0\0\0\0\x7b\x1a\
> > -\x68\xff\0\0\0\0\x7b\x1a\x60\xff\0\0\0\0\x7b\x1a\x58\xff\0\0\0\0\x7b\x1a\x50\
> > -\xff\0\0\0\0\x15\x08\x4c\x02\0\0\0\0\x6b\x1a\xd0\xff\0\0\0\0\xbf\xa3\0\0\0\0\0\
> > -\0\x07\x03\0\0\xd0\xff\xff\xff\xbf\x81\0\0\0\0\0\0\xb7\x02\0\0\x0c\0\0\0\xb7\
> > +\0\0\0\0\0\0\0\0\0\xbf\x72\0\0\0\0\0\0\x85\0\0\0\x01\0\0\0\xbf\x08\0\0\0\0\0\0\
> > +\x18\0\0\0\xff\xff\xff\xff\0\0\0\0\0\0\0\0\x15\x06\x67\x02\0\0\0\0\xbf\x87\0\0\
> > +\0\0\0\0\x15\x07\x65\x02\0\0\0\0\x71\x61\0\0\0\0\0\0\x55\x01\x01\0\0\0\0\0\x05\
> > +\0\x5e\x02\0\0\0\0\xb7\x01\0\0\0\0\0\0\x63\x1a\xc8\xff\0\0\0\0\x7b\x1a\xc0\xff\
> > +\0\0\0\0\x7b\x1a\xb8\xff\0\0\0\0\x7b\x1a\xb0\xff\0\0\0\0\x7b\x1a\xa8\xff\0\0\0\
> > +\0\x63\x1a\xa0\xff\0\0\0\0\x7b\x1a\x98\xff\0\0\0\0\x7b\x1a\x90\xff\0\0\0\0\x7b\
> > +\x1a\x88\xff\0\0\0\0\x7b\x1a\x80\xff\0\0\0\0\x7b\x1a\x78\xff\0\0\0\0\x7b\x1a\
> > +\x70\xff\0\0\0\0\x7b\x1a\x68\xff\0\0\0\0\x7b\x1a\x60\xff\0\0\0\0\x7b\x1a\x58\
> > +\xff\0\0\0\0\x15\x09\x4d\x02\0\0\0\0\x6b\x1a\xd0\xff\0\0\0\0\xbf\xa3\0\0\0\0\0\
> [...]
>
> Can we have a build system step which generates this file and compare
> with what is committed in the repository that we can run in our CI?
>
> That would avoid the need of human review of this blob.
>
Here are the steps to verify:
Pull latest archlinux/archlinux docker image and get a bash shell inside
the container. Install the required toolchain packages.
pacman -Syu --noconfirm
pacman -S --noconfirm  bpf libbpf llvm clang make

Confirm the versions:
clang 14.0.6
bpftool 7.0.0
libbpf 1.0.1

After this, ensure that the files Makefile.ebpf and rss.bpf.c from this
patch exist at /home/shreesh/c/qemu/tools/ebpf/ inside the docker.
This path seems to be important since BTF info seems to contain the absolute
path of rss.bpf.c which was compiled by clang and is embedded inside
the generated ELF object.

Run `make -C /home/shreesh/c/qemu/tools/ebpf -f Makefile.ebpf` and
verify that `sha256sum /home/shreesh/c/qemu/tools/ebpf/rss.bpf.skeleton.h` is
a54af3d1fb401ddd56c151f00ae20d6557e965c0a1a4d8ed5f8d925457158a0e which
should be the same as the one submitted as part of this patch.

I'm not familiar with QEMU's CI and am not sure if the above steps can
be converted into build system steps. However it should be doable by a
human and verify that the generated skeleton file is correct and not
tampered with.

Regards,
Shreesh