[Bug debug/99090] gsplit-dwarf broken on riscv64-linux

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99090

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:b5040344b9ca609e19ee59ba56cd4af9697a1692

commit r11-7472-gb5040344b9ca609e19ee59ba56cd4af9697a1692
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Mar 3 09:53:58 2021 +0100

    dwarf2out: Fix -gsplit-dwarf on riscv or other non-.uleb128 targets
[PR99090]

    As mentioned in the PR, riscv* only supports .uleb128 with constant
    arguments, doesn't support difference of two labels because of aggressive
    linker relaxations.  But I bet various other targets, especially those not
    using GNU assembler, might suffer from the same problem.
    As the FIXME comment in output_loc_list indicates, we ICE on
    -gsplit-dwarf on those targets whenever we need .debug_loclists, because
    we only emit DW_LLE_startx_length which requires working .uleb128 delta
    of 2 code section labels.  We can't use DW_LLE_base_addressx
    once followed by DW_LLE_offset_pair either because the latter suffers
    from the same issue - need .uleb128 difference of code section labels
    (and in that case not just for the second operand but also for the first).

    So, this patch implements what the comment said and emits
DW_LLE_startx_endx
    instead, which wastes more space in .debug_addr, but will work.

    Bootstrapped/regtested on x86_64-linux and i686-linux and as written in the
    PR, Jim has tested it on riscv*linux.  Ok for trunk?

    BTW, for HAVE_AS_LEB128 -gdwarf-5 -gsplit-dwarf, maybe we should consider
    instead of always emitting DW_LLE_startx_length do all the optimizations
    that we do for HAVE_AS_LEB128 -gdwarf-5, or at least a subset of them.
    For !have_multiple_function_sections, we in that case emit just
    DW_LLE_offset_pair (that can certainly be a win for small TUs, we wouldn't
    need any .debug_addr entry in that case; on the other side, just using
    DW_LLE_offset_pair can be harmful for very large TUs especially if the
    loclist has many entries, emitting in that case a single
DW_LLE_base_address
    or for -gsplit-dwarf DW_LLE_base_addressx followed by DW_LLE_offset_pair
    might be much smaller), and for have_multiple_function_sections figuring
    out if DW_LLE_base_address followed by DW_LLE_offset_pair entries
    or DW_LLE_start_length is bettter.  So perhaps a middle-ground for
    -gsplit-dwarf would be to always do the have_multiple_function_sections
    behavior, i.e. DW_LLE_base_addressx followed by DW_LLE_offset_pair vs.
    DW_LLE_startx_length decisions based on the ranges and their counts.
    And perhaps dwz could optimize afterwards, on linked binaries or shared
    libraries it knows all the offsets and could figure out optimal DW_LLE_*.

    2021-03-03  Jakub Jelinek  <jakub@redhat.com>

            PR debug/99090
            * dwarf2out.c (dw_loc_list_struct): Add end_entry member.
            (new_loc_list): Clear end_entry.
            (output_loc_list): Only use DW_LLE_startx_length for -gsplit-dwarf
            if HAVE_AS_LEB128, otherwise use DW_LLE_startx_endx.  Fix comment
            typo.
            (index_location_lists): For dwarf_version >= 5 without
HAVE_AS_LEB128,
            initialize also end_entry.