[Bug symtab/30357] Segmentation fault for the 'start' command

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

https://sourceware.org/bugzilla/show_bug.cgi?id=30357

--- Comment #10 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The gdb-13-branch branch has been updated by Tom de Vries
<vries@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=69eedc8e312685d9c0055098e9c461b95a2e832f

commit 69eedc8e312685d9c0055098e9c461b95a2e832f
Author: Tom de Vries <tdevries@suse.de>
Date:   Tue Apr 18 05:47:21 2023 +0200

    [gdb/symtab] Handle empty file name in .debug_line section

    With DWARF 5, it's possible to produce an empty file name in the File Name
    Table of the .debug_line section:
    ...
     The File Name Table (offset 0x112, lines 1, columns 2):
      Entry Dir     Name
      0     1       (indirect line string, offset: 0x2d):
    ...

    Currently, when gdb reads an exec containing such debug info, it segfaults:
    ...
    Thread 1 "gdb" received signal SIGSEGV, Segmentation fault.
    0x000000000072cd38 in dwarf2_start_subfile (cu=0x2badc50, fe=..., lh=...)
at \
      gdb/dwarf2/read.c:18716
    18716     if (!IS_ABSOLUTE_PATH (filename) && dirname != NULL)
    ...
    because read_direct_string transforms "" into a nullptr, and we end up
    dereferencing the nullptr.

    Note that the behaviour of read_direct_string has been present since repo
    creation.

    Fix this in read_formatted_entries, by transforming nullptr filenames in to
""
    filenames.

    Tested on x86_64-linux.

    Reviewed-By: Tom Tromey <tom@tromey.com>

    PR symtab/30357
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30357

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