[Bug symtab/25065] GDB segfaults while running gdb.cp/subtypes.exp with -flto

cvs-commit at gcc dot gnu.org sourceware-bugzilla@sourceware.org
Wed Nov 27 20:06:00 GMT 2019


--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Kevin Buettner <kevinb@sourceware.org>:


commit 8d9a2568651d55eb518d3ac6c0dd0b4719da7f77
Author: Kevin Buettner <kevinb@redhat.com>
Date:   Sat Oct 12 14:35:56 2019 -0700

    Fix BZ 25065 - Ensure that physnames are computed for inherited DIEs

    This is a fix for BZ 25065.

    GDB segfaults when running either gdb.cp/subtypes.exp or
    gdb.cp/local.exp in conjunction with using the -flto compiler/linker

    A much simpler program, which was used to help create the test for
    this fix, is:

    -- doit.cc --
    int main()
      class Foo {
        int doit ()
          return 0;

      Foo foo;

      return foo.doit ();
    -- end doit.cc --

    gcc -o doit -flto -g doit.cc
    gdb -q doit
    Reading symbols from doit...
    (gdb) ptype main::Foo
    type = class Foo {
    Segmentation fault (core dumped)

    The segfault occurs due to a NULL physname in
    c_type_print_base_struct_union in c-typeprint.c.  Specifically,
    calling is_constructor_name() eventually causes the SIGSEGV is this
    code in c-typeprint.c:

              const char *physname = TYPE_FN_FIELD_PHYSNAME (f, j);
              int is_full_physname_constructor =
                TYPE_FN_FIELD_CONSTRUCTOR (f, j)
                || is_constructor_name (physname)
                || is_destructor_name (physname)
                || method_name[0] == '~';

    However, looking at compute_delayed_physnames(), we see that
    the TYPE_FN_FIELD_PHYSNAME field should never be NULL.  This
    field will be set to "" for NULL physnames:

          physname = dwarf2_physname (mi.name, mi.die, cu);
          TYPE_FN_FIELD_PHYSNAME (fn_flp->fn_fields, mi.index)
        = physname ? physname : "";

    For this particular case, it turns out that compute_delayed_physnames
    wasn't being called, which left TYPE_FN_FIELD_PHYSNAME set to the NULL
    value that it started with when that data structure was allocated.

    The place to fix it, I think, is towards the end of

    My first attempt at fix caused the origin CU's method_list (which is
    simply the list of methods whose physnames still need to be computed)
    to be added to the CU which is doing the inheriting.  One drawback
    with this approach is that compute_delayed_physnames is (eventually)
    called with a CU that's different than the CU in which the methods
    were found.  It's not clear whether this will cause problems or not.

    A safer approach, which is what I ultimately settled on, is to call
    compute_delayed_physnames() from inherit_abstract_dies().  One
    potential drawback is that all needed types might not be known at that
    point.  However, in my testing, I haven't seen a problem along these


        * dwarf2read.c (inherit_abstract_dies): Ensure that delayed
        physnames are computed for inherited DIEs.

    Change-Id: I6c6ffe96b301a9daab9f653956b89e3a33fa9445

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