Re: [PATCH dwarves 0/4] BTF ELF writing changes

From: Giuliano Procida <gprocida@google.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: dwarves@vger.kernel.org, acme@kernel.org,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Matthias Männich" <maennich@google.com>,
	kernel-team@android.com, "Kernel Team" <kernel-team@fb.com>,
	bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH dwarves 0/4] BTF ELF writing changes
Date: Wed, 27 Jan 2021 01:10:40 +0000	[thread overview]
Message-ID: <CAGvU0H=CFBmGeNx_4zJt9ou8r31knPcq0doOi-3p5JqnaQbp7w@mail.gmail.com> (raw)
In-Reply-To: <20210126195542.GB120879@krava>

Hi.

On Tue, 26 Jan 2021 at 19:56, Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Mon, Jan 25, 2021 at 01:06:21PM +0000, Giuliano Procida wrote:
> > Hi.
> >
> > This follows on from my change to improve the error handling around
> > llvm-objcopy in libbtf.c.
> >
> > Note on recipients: Please let me know if I should adjust To or CC.
> >
> > Note on style: I've generally placed declarations as allowed by C99,
> > closest to point of use. Let me know if you'd prefer otherwise.
> >
> > 1. Improve ELF error reporting
> >
> > 2. Add .BTF section using libelf
> >
> > This shows the minimal amount of code needed to drive libelf. However,
> > it leaves layout up to libelf, which is almost certainly not wanted.
> >
> > As an unexpcted side-effect, vmlinux is larger than before. It seems
> > llvm-objcopy likes to trim down .strtab.
> >
> > 3. Manually lay out updated ELF sections
> >
> > This does full layout of new and updated ELF sections. If the update
> > ELF sections were not the last ones in the file by offset, then it can
> > leave gaps between sections.
> >
> > 4. Align .BTF section to 8 bytes
> >
> > This was my original aim.
> >
> > Regards.
> >
> > Giuliano Procida (4):
> >   btf_encoder: Improve ELF error reporting
> >   btf_encoder: Add .BTF section using libelf
> >   btf_encoder: Manually lay out updated ELF sections
> >   btf_encoder: Align .BTF section to 8 bytes
>
> hi,
> I can't apply this on dwarves git master, which commit is it based on?
>

It's based on:
https://www.spinics.net/lists/dwarves/msg00775.html (0/3)
https://www.spinics.net/lists/dwarves/msg00774.html (1/3, unrelated fix)
https://www.spinics.net/lists/dwarves/msg00773.html (2/3, this is the
one you'll need for a clean git am; obsoleted by this new series)
(3/3 was abandoned)

Arnaldo did say the two commits were applied... but perhaps they
haven't been pushed to public master yet.

> thanks,
> jirka
>

You're welcome.
Giuliano.

> >
> >  libbtf.c | 222 +++++++++++++++++++++++++++++++++++++++++++------------
> >  1 file changed, 175 insertions(+), 47 deletions(-)
> >
> > --
> > 2.30.0.280.ga3ce27912f-goog
> >
>