[Bug symtab/27541] gdb crashes on "file -readnow"

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

https://sourceware.org/bugzilla/show_bug.cgi?id=27541

--- Comment #9 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Simon Marchi <simark@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=8a91fbdf3b570460afdf0cac0d7f087b9d55f60c

commit 8a91fbdf3b570460afdf0cac0d7f087b9d55f60c
Author: Simon Marchi <simon.marchi@polymtl.ca>
Date:   Tue Mar 30 13:37:11 2021 -0400

    gdb/dwarf: disable per-BFD resource sharing for -readnow objfiles

    New in v2:

      - Disable sharing only for -readnow objfiles, not all objfiles.

    As described in PR 27541, we hit an internal error when loading a binary
    the standard way and then loading it with the -readnow option:

        $ ./gdb -nx -q --data-directory=data-directory ~/a.out -ex "set confirm
off" -ex "file -readnow ~/a.out"
        Reading symbols from /home/simark/a.out...
        Reading symbols from ~/a.out...
        /home/simark/src/binutils-gdb/gdb/dwarf2/read.c:8098: internal-error:
void create_all_comp_units(dwarf2_per_objfile*): Assertion
`per_objfile->per_bfd->all_comp_units.empty ()' failed.

    This is a recurring problem that exposes a design issue in the DWARF
    per-BFD sharing feature.  Things work well when loading a binary with
    the same method (with/without index, with/without readnow) twice in a
    row.  But they don't work so well when loading a binary with different
    methods.  See this previous fix, for example:

        efb763a5ea35 ("gdb: check for partial symtab presence in
dwarf2_initialize_objfile")

    That one handled the case where the first load is normal (uses partial
    symbols) and the second load uses an index.

    The problem is that when loading an objfile with a method A, we create a
    dwarf2_per_bfd and some dwarf2_per_cu_data and initialize them with the
    data belonging to that method.  When loading another obfile sharing the
    same BFD but with a different method B, it's not clear how to re-use the
    dwarf2_per_bfd/dwarf2_per_cu_data previously created, because they
    contain the data specific to method A.

    I think the most sensible fix would be to not share a dwarf2_per_bfd
    between two objfiles loaded with different methods.  That means that two
    objfiles sharing the same BFD and loaded the same way would share a
    dwarf2_per_bfd.  Two objfiles sharing the same BFD but loaded with
    different methods would use two different dwarf2_per_bfd structures.

    However, this isn't a trivial change.  So to fix the known issue quickly
    (including in the gdb 10 branch), this patch just disables all
    dwarf2_per_bfd sharing for objfiles using READNOW.

    Generalize the gdb.base/index-cache-load-twice.exp test to test all
    the possible combinations of loading a file with partial symtabs, index
    and readnow.  Move it to gdb.dwarf2, since it really exercises features
    of the DWARF reader.

    gdb/ChangeLog:

            PR gdb/27541
            * dwarf2/read.c (dwarf2_has_info): Don't share dwarf2_per_bfd
            with objfiles using READNOW.

    gdb/testsuite/ChangeLog:

            PR gdb/27541
            * gdb.base/index-cache-load-twice.exp: Remove.
            * gdb.base/index-cache-load-twice.c: Remove.
            * gdb.dwarf2/per-bfd-sharing.exp: New.
            * gdb.dwarf2/per-bfd-sharing.c: New.

    Change-Id: I9ffcf1e136f3e75242f70e4e58e4ba1fd3083389

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