Re: [PATCH] libbpf: Fix up generation of bpf_helper_defs.h

Stanislav Fomichev
2019-11-26T23:10:35Z

On 11/26, Andrii Nakryiko wrote:
> On Tue, Nov 26, 2019 at 2:17 PM Arnaldo Carvalho de Melo
> <arnaldo.melo@gmail.com> wrote:
> >
> > Em Tue, Nov 26, 2019 at 07:10:18PM -0300, Arnaldo Carvalho de Melo escreveu:
> > > Em Tue, Nov 26, 2019 at 02:05:41PM -0800, Andrii Nakryiko escreveu:
> > > > On Tue, Nov 26, 2019 at 11:12 AM Arnaldo Carvalho de Melo
> > > > <arnaldo.melo@gmail.com> wrote:
> > > > >
> > > > > Em Tue, Nov 26, 2019 at 07:50:44PM +0100, Toke Høiland-Jørgensen escreveu:
> > > > > > Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com> writes:
> > > > > >
> > > > > > > Em Tue, Nov 26, 2019 at 05:38:18PM +0100, Toke Høiland-Jørgensen escreveu:
> > > > > > >> Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com> writes:
> > > > > > >>
> > > > > > >> > Em Tue, Nov 26, 2019 at 12:10:45PM -0300, Arnaldo Carvalho de Melo escreveu:
> > > > > > >> >> Hi guys,
> > > > > > >> >>
> > > > > > >> >> While merging perf/core with mainline I found the problem below for
> > > > > > >> >> which I'm adding this patch to my perf/core branch, that soon will go
> > > > > > >> >> Ingo's way, etc. Please let me know if you think this should be handled
> > > > > > >> >> some other way,
> > > > > > >> >
> > > > > > >> > This is still not enough, fails building in a container where all we
> > > > > > >> > have is the tarball contents, will try to fix later.
> > > > > > >>
> > > > > > >> Wouldn't the right thing to do not be to just run the script, and then
> > > > > > >> put the generated bpf_helper_defs.h into the tarball?
> > > > >
> > > > > > > I would rather continue just running tar and have the build process
> > > > > > > in-tree or outside be the same.
> > > > > >
> > > > > > Hmm, right. Well that Python script basically just parses
> > > > > > include/uapi/linux/bpf.h; and it can be given the path of that file with
> > > > > > the --filename argument. So as long as that file is present, it should
> > > > > > be possible to make it work, I guess?
> > > > >
> > > > > > However, isn't the point of the tarball to make a "stand-alone" source
> > > > > > distribution?
> > > > >
> > > > > Yes, it is, and as far as possible without any prep, just include the
> > > > > in-source tree files needed to build it.
> > > > >
> > > > > > I'd argue that it makes more sense to just include the
> > > > > > generated header, then: The point of the Python script is specifically
> > > > > > to extract the latest version of the helper definitions from the kernel
> > > > > > source tree. And if you're "freezing" a version into a tarball, doesn't
> > > > > > it make more sense to also freeze the list of BPF helpers?
> > > > >
> > > > > Your suggestion may well even be the only solution, as older systems
> > > > > don't have python3, and that script requires it :-\
> > > > >
> > > > > Some containers were showing this:
> > > > >
> > > > > /bin/sh: 1: /git/linux/scripts/bpf_helpers_doc.py: not found
> > > > > Makefile:184: recipe for target 'bpf_helper_defs.h' failed
> > > > > make[3]: *** [bpf_helper_defs.h] Error 127
> > > > > make[3]: *** Deleting file 'bpf_helper_defs.h'
> > > > > Makefile.perf:778: recipe for target '/tmp/build/perf/libbpf.a' failed
> > > > >
> > > > > That "not found" doesn't mean what it looks from staring at the above,
> > > > > its just that:
> > > > >
> > > > > nobody@1fb841e33ba3:/tmp/perf-5.4.0$ head -1 /tmp/perf-5.4.0/scripts/bpf_helpers_doc.py
> > > > > #!/usr/bin/python3
> > > > > nobody@1fb841e33ba3:/tmp/perf-5.4.0$ ls -la /usr/bin/python3
> > > > > ls: cannot access /usr/bin/python3: No such file or directory
> > > > > nobody@1fb841e33ba3:/tmp/perf-5.4.0$
> > > > >
> > > > > So, for now, I'll keep my fix and start modifying the containers where
> > > > > this fails and disable testing libbpf/perf integration with BPF on those
> > > > > containers :-\
> > > >
> > > > I don't think there is anything Python3-specific in that script. I
> > > > changed first line to
> > > >
> > > > #!/usr/bin/env python
> > > >
> > > > and it worked just fine. Do you mind adding this fix and make those
> > > > older containers happy(-ier?).
> > >
> > > I'll try it, was trying the other way around, i.e. adding python3 to
> > > those containers and they got happier, but fatter, so I'll remove that
> > > and try your way, thanks!
> > >
> > > I didn't try it that way due to what comes right after the interpreter
> > > line:
> > >
> > > #!/usr/bin/python3
> > > # SPDX-License-Identifier: GPL-2.0-only
> > > #
> > > # Copyright (C) 2018-2019 Netronome Systems, Inc.
> > >
> > > # In case user attempts to run with Python 2.
> > > from __future__ import print_function
> >
> > And that is why I think you got it working, that script uses things
> > like:
> >
> > print('Parsed description of %d helper function(s)' % len(self.helpers),
> > file=sys.stderr)
> >
> > That python2 thinks its science fiction, what tuple is that? Can't
> > understand, print isn't a function back then.
>
> Not a Python expert (or even regular user), but quick googling showed
> that this import is the way to go to use Python3 semantics of print
> within Python2, so seems like that's fine. But maybe Quentin has
> anything to say about this.
We are using this script with python2.7, works just fine :-)
So maybe doing s/python3/python/ is the way to go, whatever
default python is installed, it should work with that.

> > https://sebastianraschka.com/Articles/2014_python_2_3_key_diff.html#the-print-function
> >
> > I've been adding python3 to where it is available and not yet in the
> > container images, most are working after that, some don't need because
> > they need other packages for BPF to work and those are not available, so
> > nevermind, lets have just the fix I provided, I'll add python3 and life
> > goes on.
> >
> > - Arnaldo