[Bug varobj/27757] -var-list-children coredump

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

https://sourceware.org/bugzilla/show_bug.cgi?id=27757

--- Comment #15 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=e25d6d93c4a0d597da2521c2c38cb1ce6e51feb8

commit e25d6d93c4a0d597da2521c2c38cb1ce6e51feb8
Author: Simon Marchi <simon.marchi@polymtl.ca>
Date:   Thu Apr 22 15:01:28 2021 -0400

    gdb: fix getting range of flexible array member in Python

    As reported in bug 27757, we get an internal error when doing:

        $ cat test.c
        struct foo {
            int len;
            int items[];
        };

        struct foo *p;

        int main() {
            return 0;
        }
        $ gcc test.c -g -O0 -o test
        $ ./gdb -q -nx --data-directory=data-directory ./test -ex 'python
gdb.parse_and_eval("p").type.target()["items"].type.range()'
        Reading symbols from ./test...
        /home/simark/src/binutils-gdb/gdb/gdbtypes.h:435: internal-error:
LONGEST dynamic_prop::const_val() const: Assertion `m_kind == PROP_CONST'
failed.
        A problem internal to GDB has been detected,
        further debugging may prove unreliable.
        Quit this debugging session? (y or n)

    This is because the Python code (typy_range) blindly reads the high
    bound of the type of `items` as a constant value.  Since it is a
    flexible array member, it has no high bound, the property is undefined.
    Since commit 8c2e4e0689 ("gdb: add accessors to struct dynamic_prop"),
    the getters check that you are not getting a property value of the wrong
    kind, so this causes a failed assertion.

    Fix it by checking if the property is indeed a constant value before
    accessing it as such.  Otherwise, use 0.  This restores the previous GDB
    behavior: because the structure was zero-initialized, this is what was
    returned before.  But now this behavior is explicit and not accidental.

    Add a test, gdb.python/flexible-array-member.exp, that is derived from
    gdb.base/flexible-array-member.exp.  It tests the same things, but
    through the Python API.  It also specifically tests getting the range
    from the various kinds of flexible array member types (AFAIK it wasn't
    possible to do the equivalent through the CLI).

    gdb/ChangeLog:

            PR gdb/27757
            * python/py-type.c (typy_range): Check that bounds are constant
            before accessing them as such.
            * guile/scm-type.c (gdbscm_type_range): Likewise.

    gdb/testsuite/ChangeLog:

            PR gdb/27757
            * gdb.python/flexible-array-member.c: New test.
            * gdb.python/flexible-array-member.exp: New test.
            * gdb.guile/scm-type.exp (test_range): Add test for flexible
            array member.
            * gdb.guile/scm-type.c (struct flex_member): New.
            (main): Use it.

    Change-Id: Ibef92ee5fd871ecb7c791db2a788f203dff2b841

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