Re: [PATCH] Fix faulty use of obstack_free() to *shrink* dont_print_statmem_obstack. Instead use obstack_blank_fast() with a "negative" size. A real stack data structured would be appropriate here. Added unit test gdb/testsuite/gdb.cp/printstaticrecursion.exp.

[Patrick Frants <osscontribute@gmail.com>]

 I am 99% sure the use of obstack_free() on line 390 (also cp-valprint.c)
is used in exactly the same way (shrinking) and is therefore also wrong.
However, I don't have a unit test for that case.

On Thu, Oct 19, 2017 at 11:29 AM, Patrick Frants <osscontribute@gmail.com>
wrote:

> Recursion detection for static members was not working because when
> popping addresses of the stack, the stack was unintentionally cleared,
> leaving the stack empty. This was caused by a call to obstack_next_free(),
> which frees the current object.
> The fix uses obstack_blank_fast with a negative size to shrink the current
> object with the desired amount.
> A unit test (gdb.cp/printstaticrecursion.exp) was added. No new
> regression has been observed in testsuite/gdb.cp/*.exp.
> ---
>  gdb/cp-valprint.c                             | 11 +++-----
>  gdb/testsuite/gdb.cp/printstaticrecursion.cc  | 21 +++++++++++++++
>  gdb/testsuite/gdb.cp/printstaticrecursion.exp | 39
> +++++++++++++++++++++++++++
>  3 files changed, 63 insertions(+), 8 deletions(-)
>  create mode 100644 gdb/testsuite/gdb.cp/printstaticrecursion.cc
>  create mode 100644 gdb/testsuite/gdb.cp/printstaticrecursion.exp
>
> diff --git a/gdb/cp-valprint.c b/gdb/cp-valprint.c
> index fb9bfd9..8f9658d 100644
> --- a/gdb/cp-valprint.c
> +++ b/gdb/cp-valprint.c
> @@ -370,14 +370,9 @@ cp_print_value_fields (struct type *type, struct type
> *real_type,
>
>           if (obstack_final_size > statmem_obstack_initial_size)
>             {
> -             /* In effect, a pop of the printed-statics stack.  */
> -
> -             void *free_to_ptr =
> -               (char *) obstack_next_free (&dont_print_statmem_obstack) -
> -               (obstack_final_size - statmem_obstack_initial_size);
> -
> -             obstack_free (&dont_print_statmem_obstack,
> -                           free_to_ptr);
> +          /* In effect, a pop of the printed-statics stack.  */
> +          size_t shrink_bytes = statmem_obstack_initial_size -
> obstack_final_size;
> +          obstack_blank_fast(&dont_print_statmem_obstack, shrink_bytes);
>             }
>
>           if (last_set_recurse != recurse)
> diff --git a/gdb/testsuite/gdb.cp/printstaticrecursion.cc
> b/gdb/testsuite/gdb.cp/printstaticrecursion.cc
> new file mode 100644
> index 0000000..616c00d
> --- /dev/null
> +++ b/gdb/testsuite/gdb.cp/printstaticrecursion.cc
> @@ -0,0 +1,21 @@
> +#include <cstdio>
> +
> +struct Inner
> +{
> +    static Inner instance;
> +};
> +
> +
> +struct Outer
> +{
> +    Inner inner;
> +    static Outer instance;
> +};
> +
> +Inner Inner::instance;
> +Outer Outer::instance;
> +
> +int main()
> +{
> +    return 0; /* break-here */
> +}
> \ No newline at end of file
> diff --git a/gdb/testsuite/gdb.cp/printstaticrecursion.exp
> b/gdb/testsuite/gdb.cp/printstaticrecursion.exp
> new file mode 100644
> index 0000000..1407c12
> --- /dev/null
> +++ b/gdb/testsuite/gdb.cp/printstaticrecursion.exp
> @@ -0,0 +1,39 @@
> +# Copyright 2008-2017 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +
> +if { [skip_cplus_tests] } { continue }
> +
> +standard_testfile printstaticrecursion.cc
> +
> +# Create and source the file that provides information about the compiler
> +# used to compile the test case.
> +if [get_compiler_info "c++"] {
> +    untested "couldn't find a valid c++ compiler"
> +    return -1
> +}
> +
> +if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug
> c++}]} {
> +    return -1
> +}
> +
> +if ![runto_main] then {
> +    perror "couldn't run to main"
> +    continue
> +}
> +
> +gdb_test "print Outer::instance" "{inner = {static instance = {static
> instance = <same as static member of an already seen type>}}, static
> instance = {inner = {static instance = {static instance = <same as static
> member of an already seen type>}}, static instance = <same as static member
> of an already seen type>}}" "Print recursive static member"
> +gdb_exit
> +return 0
> --
> 1.8.3.1
>
>