Re: Demangle symbols in debug assertion messages

[François Dumont <frs dot dumont at gmail dot com>]

On 20/05/2015 12:19, Jonathan Wakely wrote:
> On 20/05/15 11:17 +0100, Jonathan Wakely wrote:
> > On 04/05/15 22:31 +0200, François Dumont wrote:
> > > Hi
> > >
> > >   Here is  the patch to demangle symbols in debug messages. I have 
> > > also simplify code in formatter.h.
> > >
> > >   Here is an example of assertion message:
> > >
> > > /home/fdt/dev/gcc/build/x86_64-unknown-linux-gnu/libstdc++-v3/include/debug/functions.h:213: 
> > >
> > >   error: function requires a valid iterator range [__first, __last).
> > >
> > > Objects involved in the operation:
> > > iterator "__first" @ 0x0x7fff165d68b0 {
> > > type = 
> > > __gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<int*, 
> > > std::__cxx1998::vector<int, std::allocator<int> > >, 
> > > std::__debug::vector<int, std::allocator<int> > > (mutable iterator);
> > > state = dereferenceable;
> > > references sequence with type `std::__debug::vector<int, 
> > > std::allocator<int> >' @ 0x0x7fff165d69d0
> > > }
> > > iterator "__last" @ 0x0x7fff165d68e0 {
> > > type = 
> > > __gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<int*, 
> > > std::__cxx1998::vector<int, std::allocator<int> > >, 
> > > std::__debug::vector<int, std::allocator<int> > > (mutable iterator);
> > > state = dereferenceable;
> > > references sequence with type `std::__debug::vector<int, 
> > > std::allocator<int> >' @ 0x0x7fff165d69d0
> > > }
> > >
> > >
> > >   * include/debug/formatter.h (_GLIBCXX_TYPEID): New macro to simplify
> > >   usage of typeid.
> > >   (_Error_formatter::_M_print_type): New.
> > >   * src/c++11/debug.cc
> > >   (_Error_formatter::_Parameter::_M_print_field): Use latter.
> > >   (_Error_formatter::_M_print_type): Implement latter using
> > >   __cxaabiv1::__cxa_demangle to print demangled type name.
> > >
> > > I just hope that __cxa_demangle is portable.
> >
> > It's provided by GCC itself so is always available in the runtime.
> > (It is also portable, because it's defined by the Itanium C++ ABI).
> >
> >
> > > Ok to commit ?
> >
> > Yes, this is great, thanks!
>
> Does this fix https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65392 ?
With the patch this code of the bug report generates the following debug 
message:

/home/fdt/dev/gcc/build/x86_64-unknown-linux-gnu/libstdc++-v3/include/debug/safe_iterator.h:395:
    error: attempt to retreat a past-the-end iterator 2 steps, which falls
    outside its valid range.

Objects involved in the operation:
iterator @ 0x0x7fff32365c50 {
  type = 
__gnu_debug::_Safe_iterator<std::__cxx1998::_Deque_iterator<int, int&, 
int*>, std::__debug::deque<int, std::allocator<int> > > (mutable iterator);
  state = past-the-end;
  references sequence with type `std::__debug::deque<int, 
std::allocator<int> >' @ 0x0x7fff32365cd0
}

which looks nice.

However I wouldn't say that bug is fixed because debug mode do not 
generate mangle name, it simply rely on typeid to get it. Shouldn't bug 
report be saying so ? Whatever, symbol generated by typeid can be 
demangle by __cxa_demangle so it mustn't be that bad.

François