Re: WIP _GLIBCXX_DEBUG backtrace

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On Mon, 4 Jul 2022, 18:21 François Dumont via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:

> Hi
>
> Here is the patch to add backtrace to _GLIBCXX_DEBUG mode. It is using
> the recently introduced _GLIBCXX_HAS_STACKTRACE.
>
> It is only WIP because for the moment I had to add:
>
> // { dg-options "-lstdc++_libbacktrace" }
>
> to avoid unresolved symbols.
>
> How should I handle this ?
>
> 1. Ask the user to define _GLIBCXX_DEBUG_STACKTRACE to get the backtrace
> and so also require to add this linker option.
>

For now, I think this is the best option. Even when the symbols are in the
library I think the backtraces should be optional. Controlled by a
compile-time macro and/or an environment variable.


> 2. Is it possible to add something in formatter.h to automagically link
> libstdc++_libbacktrace ?
>

Not possible, GCC and Unix linkers don't support doing that.


> 3. Add symbols to libstdc++.so ?
>

The symbols from libstdc++_libbacktrace.a will move to the .so at some
point, once the C++23 std::stacktrace implementation is stable. I don't
know if that will happen for GCC 13 though, it might be GCC 14.



> Output sample:
>
>
> /home/fdt/dev/gcc/build/x86_64-pc-linux-gnu/libstdc++-v3/include/debug/vector:264:
> In function:
>      void std::debug::vector<_Tp, _Allocator>::assign(_InputIterator,
>      _InputIterator) [with _InputIterator = const int*;
>      <template-parameter-2-2> = void; _Tp = int; _Allocator =
>      std::allocator<int>]
>
> Backtrace:
>      0x40284a void std::debug::vector<int, std::allocator<int>
>  >::assign<int const*, void>(int const*, int const*)
>
> /home/fdt/dev/gcc/build/x86_64-pc-linux-gnu/libstdc++-v3/include/debug/vector:264
>      0x402bed void gnu_test::check_assign1<std::debug::vector<int,
> std::allocator<int> > >()
> /home/fdt/dev/gcc/git/libstdc++-v3/testsuite/util/debug/checks.h:111
>      0x40246c test01()
>
> /home/fdt/dev/gcc/git/libstdc++-v3/testsuite/23_containers/vector/debug/assign4_neg.cc:26
>      0x40246c main
>
> /home/fdt/dev/gcc/git/libstdc++-v3/testsuite/23_containers/vector/debug/assign4_neg.cc:31
>
> Error: function requires a valid iterator range [first, last).
>
> Objects involved in the operation:
>      iterator "first" @ 0x7ffe09e62fd8 {
>        type = int const* (constant iterator);
>      }
>      iterator "last" @ 0x7ffe09e62fd0 {
>        type = int const* (constant iterator);
>      }
> XFAIL: 23_containers/vector/debug/assign4_neg.cc execution test
>
> François
>
>