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Date:   Sun, 27 Dec 2020 19:47:57 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Jakub Jelinek <jakub@...hat.com>,
        Fangrui Song <maskray@...gle.com>,
        Caroline Tice <cmtice@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Nick Clifton <nickc@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH v3 0/2] Kbuild: DWARF v5 support

On Fri, Dec 4, 2020 at 2:13 AM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
>
> sigh...I ran a broken script to send the series which doesn't cc folks properly.
> + lkml, linux-kbuild
> (Might just resend, properly)
>
> On Thu, Dec 3, 2020 at 5:11 PM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> >
> > DWARF v5 is the latest standard of the DWARF debug info format.
> >
> > DWARF5 wins significantly in terms of size when mixed 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.
> >
> > Changes from v2:
> > * Drop two of the earlier patches that have been accepted already.
> > * Add measurements with GCC 10.2 to commit message.
> > * Update help text as per Arvind with help from Caroline.
> > * Improve case/wording between DWARF Versions as per Masahiro.
> >
> > Changes from the RFC:
> > * split patch in 3 patch series, include Fangrui's patch, too.
> > * prefer `DWARF vX` format, as per Fangrui.
> > * use spaces between assignment in Makefile as per Masahiro.
> > * simplify setting dwarf-version-y as per Masahiro.
> > * indent `prompt` in Kconfig change as per Masahiro.
> > * remove explicit default in Kconfig as per Masahiro.
> > * add comments to test_dwarf5_support.sh.
> > * change echo in test_dwarf5_support.sh as per Masahiro.
> > * remove -u from test_dwarf5_support.sh as per Masahiro.
> > * add a -gdwarf-5 cc-option check to Kconfig as per Jakub.
> >

I have tested v3 on top of Linux v5.10.3 on Debian/testing AMD64.

Numbers talk - bullshit walks. [ Linus Torvalds ]

[ 5.10.3-1-amd64-gcc10-bfd ]

GNU-toolchain: GCC v10.2.1 and GNU/ld BFD v2.35.1

503096  vmlinux
6864    vmlinux.compressed
580104  vmlinux.o

701856  linux-image-5.10.3-1-amd64-gcc10-bfd-dbg_5.10.3-1~bullseye+dileks1_amd64.deb

[ 5.10.3-1-amd64-clang-ias ]

LLVM-toolchain: Clang and LLD v11.0.1-rc2

358424  vmlinux
7032    vmlinux.compressed
353788  vmlinux.o

508336  linux-image-5.10.3-1-amd64-clang-ias-dbg_5.10.3-1~bullseye+dileks1_amd64.deb

[ 5.10.3-1-amd64-gcc10-bfd ]

$ llvm-dwarfdump-11 vmlinux.o | head -15
error: vmlinux.o:       file format elf64-x86-64

.debug_info contents:
decoding address ranges: invalid range list offset 0x265
0x00000000: Compile Unit: length = 0x0000001f, format = DWARF32,
version = 0x0005, unit_type = DW_UT_compile, abbr_offset = 0x0000,
addr_size = 0x08 (next unit at 0x00
000023)

0x0000000c: DW_TAG_compile_unit
             DW_AT_stmt_list   (0x00000000)
             DW_AT_ranges      (0x0000000c
                [0x0000000000000000, 0x000000000000021c)
                [0x0000000000000000, 0x000000000000019e)
                [0x0000000000000000, 0x0000000000002000))
             DW_AT_name        ("head_64.S")
             DW_AT_comp_dir    ("/home/dileks/src/linux-kernel/git")
             DW_AT_producer    ("GNU AS 2.35.1")
             DW_AT_language    (DW_LANG_Mips_Assembler)

[ 5.10.3-1-amd64-clang-ias ]

$ llvm-dwarfdump-11 vmlinux.o | head -15
vmlinux.o:      file format elf64-x86-64

.debug_info contents:
0x00000000: Compile Unit: length = 0x00000377, format = DWARF32,
version = 0x0005, unit_type = DW_UT_compile, abbr_offset = 0x0000,
addr_size = 0x08 (next unit at 0x00
00037b)

0x0000000c: DW_TAG_compile_unit
             DW_AT_stmt_list   (0x00000000)
             DW_AT_ranges      (0x0000000c
                [0x0000000000000000, 0x0000000000002000)
                [0x0000000000000000, 0x000000000000021c)
                [0x0000000000000000, 0x000000000000019e))
             DW_AT_name        ("arch/x86/kernel/head_64.S")
             DW_AT_comp_dir    ("/home/dileks/src/linux-kernel/git")
             DW_AT_producer    ("Debian clang version 11.0.1-+rc2-1")
             DW_AT_language    (DW_LANG_Mips_Assembler)

Attached are my kernel config files.

Feel free to add my:

Tested-by: Sedat Dilek <sedat.dilek@...il.com>

- sed@ -

> > Nick Desaulniers (2):
> >   Kbuild: make DWARF version a choice
> >   Kbuild: implement support for DWARF v5
> >
> >  Makefile                          | 15 +++++++------
> >  include/asm-generic/vmlinux.lds.h |  6 +++++-
> >  lib/Kconfig.debug                 | 35 ++++++++++++++++++++++++++-----
> >  scripts/test_dwarf5_support.sh    |  9 ++++++++
> >  4 files changed, 53 insertions(+), 12 deletions(-)
> >  create mode 100755 scripts/test_dwarf5_support.sh
> >
> > --
> > 2.29.2.576.ga3fc446d84-goog
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers
>
> --
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Download attachment "config-5.10.3-1-amd64-gcc10-bfd" of type "application/octet-stream" (235775 bytes)

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