Bug 28728

Also, it seems, debugedit is unable to extract source list from such binary.

(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).

(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

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.

(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.

*** Bug 29773 has been marked as a duplicate of this bug. ***

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.

https://inbox.sourceware.org/debugedit/20231204223100.3495057-1-mark@klomp.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>

Mark,

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

(In reply to Vitaly Chikunov from comment #10)
> Thanks the fix! But, since LLVM 18 is started to produce DWARF 5 by default,
> maybe you can draft a release with it?

I found some other bugs that cause issues with strx. Will post them soon.
Current work in progress here:
https://code.wildebeest.org/git/user/mjw/debugedit/log/?h=strx
Then do a new release after those get integrated.