[Bug debugedit/28728] New: Unknown DWARF DW_FORM_0x25

[Bug debugedit/28728] New: Unknown DWARF DW_FORM_0x25

[vt at altlinux dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

            Bug ID: 28728
           Summary: Unknown DWARF DW_FORM_0x25
           Product: debugedit
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: debugedit
          Assignee: unassigned at sourceware dot org
          Reporter: vt at altlinux dot org
                CC: debugedit at sourceware dot org
  Target Milestone: ---

Created attachment 13884
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13884&action=edit
Example of compiled module

When building Linux kernel with[1] CC=clang LLVM=1 and
CONFIG_DEBUG_INFO_DWARF5=y debugedit reports error when processing compiled
kernel modules, such as

  debugedit:
./lib/modules/5.16.0+rc6.20211223-drm-tip-alt1/kernel/sound/usb/caiaq/snd-usb-caiaq.ko:
Unknown DWARF DW_FORM_0x25

[1] https://www.kernel.org/doc/html/latest/kbuild/llvm.html

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[Bug debugedit/28728] Unknown DWARF DW_FORM_0x25

[vt at altlinux dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

--- Comment #1 from Vitaly Chikunov <vt at altlinux dot org> ---
Also, it seems, debugedit is unable to extract source list from such binary.

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[Bug debugedit/28728] Unknown DWARF DW_FORM_0x25 (DW_FORM_strx)

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

Mark Wielaard <mark at klomp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
                 CC|                            |mark at klomp dot org
            Summary|Unknown DWARF DW_FORM_0x25  |Unknown DWARF DW_FORM_0x25
                   |                            |(DW_FORM_strx)
   Last reconfirmed|                            |2021-12-27
     Ever confirmed|0                           |1

--- Comment #2 from Mark Wielaard <mark at klomp dot org> ---
(In reply to Vitaly Chikunov from comment #0)
> When building Linux kernel with[1] CC=clang LLVM=1 and
> CONFIG_DEBUG_INFO_DWARF5=y debugedit reports error when processing compiled
> kernel modules, such as
> 
>   debugedit:
> ./lib/modules/5.16.0+rc6.20211223-drm-tip-alt1/kernel/sound/usb/caiaq/snd-
> usb-caiaq.ko: Unknown DWARF DW_FORM_0x25

That is DW_FORM_strx1, which is only partially supported by debugedit. Normally
the DW_FORM_strx forms are only used when generating split DWARF (.dwo) files.
Best workaround for now is to not use DWARF5 with llvm (which isn't the default
for clang/llvm anyway).

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[Bug debugedit/28728] Unknown DWARF DW_FORM_0x25 (DW_FORM_strx)

[telans at posteo dot de]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

James Beddek <telans at posteo dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |telans at posteo dot de

--- Comment #3 from James Beddek <telans at posteo dot de> ---
(In reply to Mark Wielaard from comment #2)
> (In reply to Vitaly Chikunov from comment #0)
> > When building Linux kernel with[1] CC=clang LLVM=1 and
> > CONFIG_DEBUG_INFO_DWARF5=y debugedit reports error when processing compiled
> > kernel modules, such as
> > 
> >   debugedit:
> > ./lib/modules/5.16.0+rc6.20211223-drm-tip-alt1/kernel/sound/usb/caiaq/snd-
> > usb-caiaq.ko: Unknown DWARF DW_FORM_0x25
> 
> That is DW_FORM_strx1, which is only partially supported by debugedit.
> Normally the DW_FORM_strx forms are only used when generating split DWARF
> (.dwo) files. Best workaround for now is to not use DWARF5 with llvm (which
> isn't the default for clang/llvm anyway).

DWARFv5 is now the default with the upcoming Clang 14.0.0 release:
https://github.com/llvm/llvm-project/blob/e80c52986e1bb3afa6a92c58b1cb897877923a66/clang/docs/ReleaseNotes.rst#dwarf-support-in-clang

At the moment debugedit warns for almost any binary compiled with Clang
14.0.0-rc1

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[Bug debugedit/28728] Unknown DWARF DW_FORM_0x25 (DW_FORM_strx)

[telans at posteo dot de]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

--- Comment #4 from James Beddek <telans at posteo dot de> ---
Additionally from what I can tell the flags to re-enable DWARFv4, -gdwarf-4,
and -fdebug-default-version=4 do nothing to silence this issue.

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[Bug debugedit/28728] Unknown DWARF DW_FORM_0x25 (DW_FORM_strx)

[sam at gentoo dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

--- Comment #5 from Sam James <sam at gentoo dot org> ---
(In reply to James Beddek from comment #4)
> Additionally from what I can tell the flags to re-enable DWARFv4, -gdwarf-4,
> and -fdebug-default-version=4 do nothing to silence this issue.

CC=clang CFLAGS="-gdwarf-4 -fdebug-default-version=4" ... doesn't give a
warning for me at least. This has been bugging me for a while, glad I found it.

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[Bug debugedit/28728] Unknown DWARF DW_FORM_0x25 (DW_FORM_strx)

[sam at gentoo dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

Sam James <sam at gentoo dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bero at lindev dot ch

--- Comment #6 from Sam James <sam at gentoo dot org> ---
*** Bug 29773 has been marked as a duplicate of this bug. ***

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[Bug debugedit/28728] Unknown DWARF DW_FORM_0x25 (DW_FORM_strx)

[seppo.yliolli at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

Seppo Yli-Olli <seppo.yliolli at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |seppo.yliolli at gmail dot com

--- Comment #7 from Seppo Yli-Olli <seppo.yliolli at gmail dot com> ---
This is now reproducing basically everywhere where LLVM17 clang is used. The
workaround to use DWARF4 seems quite unexpected now that DWARF5 is these days
the norm for everything.

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[Bug debugedit/28728] Unknown DWARF DW_FORM_0x25 (DW_FORM_strx)

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

Mark Wielaard <mark at klomp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

--- Comment #8 from Mark Wielaard <mark at klomp dot org> ---
https://inbox.sourceware.org/debugedit/20231204223100.3495057-1-mark@klomp.org/

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[Bug debugedit/28728] Unknown DWARF DW_FORM_0x25 (DW_FORM_strx)

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

Mark Wielaard <mark at klomp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #9 from Mark Wielaard <mark at klomp dot org> ---
commit 3e7aeeab4f744ad15108775685db68d3a35b0735
Author: Mark Wielaard <mark@klomp.org>
Date:   Thu Mar 23 18:07:40 2023 +0100

    debugedit: Add support for .debug_str_offsets (DW_FORM_strx)

    In theory supporting strx .debug_str_offsets is easy, the strings in
    .debug_str are just read through an indirection table. When the
    strings are updated in .debug_str we just need to rewrite the
    indirection table.

    The tricky part is the ET_REL (object files or kernel modules)
    support. Relocation reading is "global" per section and we expect to
    read a relocation only once. But we need to read the
    DW_AT_str_offsets_base before reading any strx form attributes. So we
    read that first, then reset the relptr. And when we read from the
    .debug_str_offsets section we need to save and restore the .debug_info
    relptr.

            * tools/debugedit.c (do_read_24): New function.
            (str_offsets_base): New static variable.
            (buf_read_ule24): New function.
            (buf_read_ube24): Likewise.
            (setup_relbuf): Handle .debug_str_offsets.
            (do_read_uleb128): New function.
            (do_read_str_form_relocated): Likewise.
            (read_abbrev): Handle DW_FORM_strx[1234].
            (edit_strp): Take the actual string form as argument.
            Use do_read_str_form_relocated.
            (read_dwarf5_line_entries): Pass form to edit_strp.
            (edit_attributes_str_comp_dir): Take the actual string
            form as argument. Use do_read_str_form_relocated.
            (edit_attributes): Handle DW_FORM_strx[1234].
            (edit_info): Read DW_AT_str_offsets_base first.
            (update_str_offsets): New function.
            (edit_dwarf2): Setup do_read_24. Call update_str_offsets.

    https://sourceware.org/bugzilla/show_bug.cgi?id=28728

    Signed-off-by: Mark Wielaard <mark@klomp.org>

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[Bug debugedit/28728] Unknown DWARF DW_FORM_0x25 (DW_FORM_strx)

[vt at altlinux dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28728

--- Comment #10 from Vitaly Chikunov <vt at altlinux dot org> ---
Mark,

Thanks the fix! But, since LLVM 18 is started to produce DWARF 5 by default,
maybe you can draft a release with it?

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