Re: [PATCH dwarves 0/2] dwarf_loader: improve cus__merging_cu()

From: Bill Wendling <morbo@google.com>
To: Yonghong Song <yhs@fb.com>
Cc: "Arnaldo Carvalho de Melo" <arnaldo.melo@gmail.com>,
	dwarves@vger.kernel.org, "Alexei Starovoitov" <ast@kernel.org>,
	"Andrii Nakryiko" <andrii@kernel.org>, bpf <bpf@vger.kernel.org>,
	"David Blaikie" <dblaikie@gmail.com>,
	"Fāng-ruì Sòng" <maskray@google.com>,
	kernel-team@fb.com, "Nick Desaulniers" <ndesaulniers@google.com>
Subject: Re: [PATCH dwarves 0/2] dwarf_loader: improve cus__merging_cu()
Date: Fri, 2 Apr 2021 12:44:50 -0700	[thread overview]
Message-ID: <CAGG=3QXkvwrm_tnsYtJ-gvHw8Emv5xFWeckoPoD4PhEud7v8EA@mail.gmail.com> (raw)
In-Reply-To: <06ba2ed4-2730-9ce8-0665-3c720bc786a3@fb.com>

I tried porting the .config we're using to the official branch and
couldn't replicate the problem. It's probably something local.

-bw

On Thu, Apr 1, 2021 at 3:00 PM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 4/1/21 1:56 PM, Bill Wendling wrote:
> > On Thu, Apr 1, 2021 at 12:35 PM Bill Wendling <morbo@google.com> wrote:
> >>
> >> On Wed, Mar 31, 2021 at 7:58 PM Yonghong Song <yhs@fb.com> wrote:
> >>>
> >>> Function cus__merging_cu() is introduced in Commit 39227909db3c
> >>> ("dwarf_loader: Permit merging all DWARF CU's for clang LTO built
> >>> binary") to test whether cross-cu references may happen.
> >>> The original implementation anticipates compilation flags
> >>> in dwarf, but later some concerns about binary size surfaced
> >>> and the decision is to scan .debug_abbrev as a faster way
> >>> to check cross-cu references. Also putting a note in vmlinux
> >>> to indicate whether lto is enabled for built or not can
> >>> provide a much faster way.
> >>>
> >>> This patch set implemented this two approaches, first
> >>> checking the note (in Patch #2), if not found, then
> >>> check .debug_abbrev (in Patch #1).
> >>>
> >>> Yonghong Song (2):
> >>>    dwarf_loader: check .debug_abbrev for cross-cu references
> >>>    dwarf_loader: check .notes section for lto build info
> >>>
> >>>   dwarf_loader.c | 76 ++++++++++++++++++++++++++++++++++++--------------
> >>>   1 file changed, 55 insertions(+), 21 deletions(-)
> >>>
> >> With this series of patches, the compilation passes for me with
> >> ThinLTO. You may add this if you like:
> >>
> >> Tested-by: Bill Wendling <morbo@google.com>
> >
> > I did notice these warnings following the "pahole -J .tmp_vmlinux.btf"
> > command. I don't know the severity of them, but it might be good to
> > investigate.
> >
> > $ ./tools/bpf/resolve_btfids/resolve_btfids vmlinux
> >    BTFIDS  vmlinux
> > WARN: multiple IDs found for 'inode': 355, 8746 - using 355
> > WARN: multiple IDs found for 'file': 588, 8779 - using 588
> > WARN: multiple IDs found for 'path': 411, 8780 - using 411
> > WARN: multiple IDs found for 'seq_file': 1414, 8836 - using 1414
> > WARN: multiple IDs found for 'vm_area_struct': 538, 8873 - using 538
> > WARN: multiple IDs found for 'task_struct': 28, 8880 - using 28
> > WARN: multiple IDs found for 'inode': 355, 9484 - using 355
> > WARN: multiple IDs found for 'file': 588, 9517 - using 588
> > WARN: multiple IDs found for 'path': 411, 9518 - using 411
> > WARN: multiple IDs found for 'seq_file': 1414, 9578 - using 1414
> > WARN: multiple IDs found for 'vm_area_struct': 538, 9615 - using 538
> > WARN: multiple IDs found for 'task_struct': 28, 9622 - using 28
> > WARN: multiple IDs found for 'seq_file': 1414, 12223 - using 1414
> > WARN: multiple IDs found for 'file': 588, 12237 - using 588
> > WARN: multiple IDs found for 'path': 411, 12238 - using 411
> > ...
>
> I didn't see it with my config. Maybe you can share your config file?
>
> >
> > -bw
> >