Re: Demangle symbols in debug assertion messages

["François Dumont" <frs.dumont@gmail.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