[Bug gdb/23743] GDB index file mmapping broken, ubsan => runtime error: load of misaligned address

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

https://sourceware.org/bugzilla/show_bug.cgi?id=23743

--- Comment #20 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom Tromey <tromey@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=42c2c69462fd83db2e0532ee57c44091bc1032f9

commit 42c2c69462fd83db2e0532ee57c44091bc1032f9
Author: Tom Tromey <tom@tromey.com>
Date:   Sat Apr 17 13:56:36 2021 -0600

    Handle unaligned mapping of .gdb_index

    The .gdb_index was designed such that all data would be aligned.
    Unfortunately, we neglected to require this alignment in the objcopy
    instructions in the manual.  As a result, in many cases, a .gdb_index
    in the wild will not be properly aligned by mmap.  This yields
    undefined behavior, which is PR gdb/23743.

    This patch fixes the bug by always assuming that the mapping is
    unaligned, and using extract_unsigned_integer when needed.  A new
    helper class is introduced to make this less painful.

    gdb/ChangeLog
    2021-04-17  Tom Tromey  <tom@tromey.com>

            PR gdb/23743:
            * dwarf2/read.c (class offset_view): New.
            (struct symbol_table_slot): Remove.
            (struct mapped_index) <symbol_table, constant_pool>: Change type.
            <symbol_name_index, symbol_vec_index>: New methods.
            <symbol_name_slot_invalid, symbol_name_at, symbol_name_count>:
            Rewrite.
            (read_gdb_index_from_buffer): Update.
            (struct dw2_symtab_iterator) <vec>: Change type.
            (dw2_symtab_iter_init_common, dw2_symtab_iter_init)
            (dw2_symtab_iter_next, dw2_expand_marked_cus): Update.
            * dwarf2/index-write.c (class data_buf) <append_data>: Remove.
            <append_array, append_offset>: New methods.
            (write_hash_table, add_address_entry, write_gdbindex_1)
            (write_debug_names): Update.
            * dwarf2/index-common.h (byte_swap, MAYBE_SWAP): Remove.

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