[Bug symtab/26327] GDB hangs in get_builder() due to recursive ancestor pointers

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

https://sourceware.org/bugzilla/show_bug.cgi?id=26327

--- Comment #16 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom de Vries <vries@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=4cf88725da1cb503be04d3237354105ec170bc86

commit 4cf88725da1cb503be04d3237354105ec170bc86
Author: Tom de Vries <tdevries@suse.de>
Date:   Fri May 7 12:13:05 2021 +0200

    [gdb/symtab] Fix infinite recursion in dwarf2_cu::get_builder()

    With the test-case attached in PR26327, gdb aborts:
    ...
    $ gdb -q -batch 447.dealII -ex "b main"
    Aborted (core dumped)
    ...
    when running out of stack due to infinite recursion:
    ...
     #8  0x00000000006aaba6 in dwarf2_cu::get_builder (this=0x35e4b40)
         at src/gdb/dwarf2/read.c:700
     #9  0x00000000006aaba6 in dwarf2_cu::get_builder (this=0x22ee2c0)
         at src/gdb/dwarf2/read.c:700
     #10 0x00000000006aaba6 in dwarf2_cu::get_builder (this=0x35e4b40)
         at src/gdb/dwarf2/read.c:700
     #11 0x00000000006aaba6 in dwarf2_cu::get_builder (this=0x22ee2c0)
         at src/gdb/dwarf2/read.c:700
    ...

    We're recursing in this code in dwarf2_cu::get_builder():
    ...
         /* Otherwise, search ancestors for a valid builder.  */
         if (ancestor != nullptr)
           return ancestor->get_builder ();
    ...
    due to the fact that the ancestor chain is a cycle.

    Higher up in the call stack, we find some code that is responsible for
    triggering this, in new_symbol:
    ...
           case DW_TAG_formal_parameter:
             {
               /* If we are inside a function, mark this as an argument.  If
                  not, we might be looking at an argument to an inlined
function
                  when we do not have enough information to show inlined
frames;
                  pretend it's a local variable in that case so that the user
can
                  still see it.  */
               struct context_stack *curr
                 = cu->get_builder ()->get_current_context_stack ();
               if (curr != nullptr && curr->name != nullptr)
                 SYMBOL_IS_ARGUMENT (sym) = 1;
    ...

    This is code that was added to support pre-4.1 gcc, to be able to show
    arguments of inlined functions as locals, in the absense of sufficiently
    correct debug information.

    Removing this code (that is, doing SYMBOL_IS_ARGUMENT (sym) = 1
    unconditially), fixes the crash.  The ancestor variable also seems to have
    been added specifically to deal with fallout from this code, so remove that
as
    well.

    Tested on x86_64-linux:
    - openSUSE Leap 15.2 with gcc 7.5.0, and
    - openSUSE Tumbleweed with gcc 10.3.0.

    gdb/ChangeLog:

    2021-05-07  Tom de Vries  <tdevries@suse.de>

            PR symtab/26327
            * dwarf2/read.c (struct dwarf2_cu): Remove ancestor.
            (dwarf2_cu::get_builder): Remove ancestor-related code.
            (new_symbol): Remove code supporting pre-4.1 gcc that show
arguments
            of inlined functions as locals.
            (follow_die_offset, follow_die_sig_1): Remove setting of ancestor.

    gdb/doc/ChangeLog:

    2021-05-07  Tom de Vries  <tdevries@suse.de>

            PR symtab/26327
            * gdb.texinfo (Inline Functions): Update.

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