From: Ilya Leoshkevich <iii@linux.ibm.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>,
Andrii Nakryiko <andrii@kernel.org>,
dwarves@vger.kernel.org, bpf <bpf@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Yonghong Song <yhs@fb.com>, Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>
Subject: Re: [PATCH v4 dwarves] btf: Add support for the floating-point types
Date: Wed, 10 Mar 2021 22:02:49 +0100 [thread overview]
Message-ID: <ff68a62e776ce9e459bece7ae87cc53573500a50.camel@linux.ibm.com> (raw)
In-Reply-To: <CAEf4BzY0++YuU7+a3vSfWWZNLoov7mu7Q1ty4FqqH78gkqgqQw@mail.gmail.com>
On Wed, 2021-03-10 at 12:25 -0800, Andrii Nakryiko wrote:
> On Wed, Mar 10, 2021 at 12:16 PM Ilya Leoshkevich <iii@linux.ibm.com>
> wrote:
> >
> > Some BPF programs compiled on s390 fail to load, because s390
> > arch-specific linux headers contain float and double types.
> >
> > Fix as follows:
> >
> > - Make the DWARF loader fill base_type.float_type.
> >
> > - Introduce the --btf_gen_floats command-line parameter, so that
> > pahole could be used to build both the older and the newer
> > kernels.
> >
> > - libbpf introduced the support for the floating-point types in
> > commit
> > 986962fade5, so update the libbpf submodule to that version and
> > use
> > the new btf__add_float() function in order to emit the floating-
> > point
> > types when not in the compatibility mode.
> >
> > - Make the BTF loader recognize the new BTF kind.
> >
> > Example of the resulting entry in the vmlinux BTF:
> >
> > [7164] FLOAT 'double' size=8
> >
> > when building with:
> >
> > LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} --btf_gen_floats
> >
> > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> > ---
>
> So it looks good to me overall, but here's the question about using
> this --btf-gen-floats flag from link-vmlinux.sh script. If you
> specify
> that flag for an old pahole, it will probably error out, right? So
> that means we'll need to do feature detection for pahole supported
> features, right?..
I was planning to just bump the version in this check:
if [ "${pahole_ver}" -lt "116" ]; then
But we could also keep allowing 1.16-1.20 and pass the new flag on
1.21+ only.
What do you think?
next prev parent reply other threads:[~2021-03-10 21:03 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-10 20:15 [PATCH v4 dwarves] btf: Add support for the floating-point types Ilya Leoshkevich
2021-03-10 20:25 ` Andrii Nakryiko
2021-03-10 21:02 ` Ilya Leoshkevich [this message]
2021-03-10 21:35 ` Andrii Nakryiko
2021-03-11 17:46 ` Arnaldo Carvalho de Melo
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