Re: [PATCH bpf-next] bpf: Generate BTF_KIND_FLOAT when linking vmlinux

[Arnaldo Carvalho de Melo <acme@redhat.com>]

Em Tue, Mar 30, 2021 at 11:28:36PM -0700, Andrii Nakryiko escreveu:
> On Tue, Mar 30, 2021 at 6:44 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote:
> >
> > pahole v1.21 will support the --btf_gen_floats flag, which makes it
> > generate the information about the floating-point types.
> >
> > Adjust link-vmlinux.sh to pass this flag to pahole in case it's
> > supported. Whether or not this flag is supported is determined by
> > probing, which is chosen over version check for two reasons:
> >
> > 1) at this moment --btf_gen_floats exists only in master, which
> >    identifies itself as v1.20.
> > 2) distros may backport features, making the version check too
> >    conservative.
> >
> 
> Does anyone really cherry-pick and backport pahole patches, though? So
> far we've been using strictly version checks for pahole (1.13, then
> 1.16, then 1.19 for modules), that keeps everything simpler and more
> reliable, IMO. I'd stick with 1.21 check and just check with Arnaldo
> when he's planning to release a new version.

The plan is to get 1.21 out of the door when we finish the LTO work, which should be soon.

- Arnaldo
 
> > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> > ---
> >  scripts/link-vmlinux.sh | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> > index 3b261b0f74f0..f4c763d2661d 100755
> > --- a/scripts/link-vmlinux.sh
> > +++ b/scripts/link-vmlinux.sh
> > @@ -227,8 +227,13 @@ gen_btf()
> >
> >         vmlinux_link ${1}
> >
> > +       local paholeopt=-J
> > +       if ${PAHOLE} --btf_gen_floats --help >/dev/null 2>&1; then
> > +               paholeopt="${paholeopt} --btf_gen_floats"
> > +       fi
> > +
> >         info "BTF" ${2}
> > -       LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
> > +       LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} ${paholeopt} ${1}
> 
> we know that -J is always specified, so I'd leave it intact, and just
> have "extra pahole options", potentially empty.
> 
> >
> >         # Create ${2} which contains just .BTF section but no symbols. Add
> >         # SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all
> > --
> > 2.29.2
> >