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Date:   Fri, 29 Jan 2021 16:58:18 -0800
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Subject: Re: [PATCH v6 0/2] Kbuild: DWARF v5 support
To:     Nick Desaulniers <ndesaulniers@google.com>,
        Sedat Dilek <sedat.dilek@gmail.com>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Jakub Jelinek <jakub@redhat.com>,
        Caroline Tice <cmtice@google.com>,
        Nick Clifton <nickc@redhat.com>, Yonghong Song <yhs@fb.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
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On Fri, Jan 29, 2021 at 4:46 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@googlegroups.com> wrote:
>
> On Fri, Jan 29, 2021 at 4:08 PM Sedat Dilek <sedat.dilek@gmail.com> wrote=
:
> >
> > On Fri, Jan 29, 2021 at 8:43 PM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > DWARF v5 is the latest standard of the DWARF debug info format.
> > >
> > > DWARF5 wins significantly in terms of size and especially so when mix=
ed
> > > with compression (CONFIG_DEBUG_INFO_COMPRESSED).
> > >
> > > Link: http://www.dwarfstd.org/doc/DWARF5.pdf
> > >
> > > Patch 1 is a cleanup that lays the ground work and isn't DWARF
> > > v5 specific.
> > > Patch 2 implements Kconfig and Kbuild support for DWARFv5.
> > >
> >
> > When you will do a v7...
> >
> > Can you look also at places where we have hardcoded DWARF-2 handling...
>
> Ah, sorry, I just saw this now, after sending v7.  Can we wait to
> purge DWARF v2 until after we have DWARF v5?
>
> In fact, if they are orthogonal like I suspect, why don't you send
> some patches and I will help you test them?
> --
> Thanks,
> ~Nick Desaulniers

Basically the distinction is just between DWARF v2 .debug_line and
DWARF v5 .debug_line .
(-gdwarf-4 adds an extra maximum_operations_per_instruction (constant
1) compared with -gdwarf-2 but that can mostly be ignored).

Refinement among -gdwarf-[234] just clarifies things and is not going
to affect debugging experience in any case.
So I agree with Nick that it can be done separately.
Note: such clarification can make things a bit ugly because binutils
before 2020 does not recognize -gdwarf-[345].


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