[Bug 284953] typeid() returns mangled string that can't be demangled

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=284953

--- Comment #11 from Mark Millard <marklmi26-fbsd@yahoo.com> ---
(In reply to Dimitry Andric from comment #2)
(In reply to Mark Millard from comment #10)

Context: Itanium C++ ABI

Another relevant section is the one about  __cxa_demangle(. . .).
Turns out it is very explicit about the _Z vs. not for the
use of std::type_info::name() results for that routine:

QUOTE
3.4 Demangler API

Synopsis:

namespace abi {
  extern "C" char* __cxa_demangle (const char* mangled_name,
                                   char* buf,
                                   size_t* n,
                                   int* status);
}
mangled-name is a pointer to a null-terminated array of characters.
It may be either an external name, i.e. with a "_Z" prefix,
or an internal NTBS mangling, e.g. of a type for type_info.
END QUOTE

So: Adding the _Z should not be required for decoding
std::type_info::name() results via use of __cxa_demangle( . . . ) .

If the Itanium C++ ABI is the context involved, then it looks like
this buzilla should be reopened and the upstream fix would be to
the __cxa_demangle implementation so that it does not require
_Z for what std::type_info::name() returns.

I cannot change the status.

Also:
The wording of 3.4 suggests that there may be other internal NTBS
naming that also should not require the _Z prefix. It looks like
separately adding a _Z prefix would be more of a work-around than
an actual fix. Knowing when to apply the workaround vs. not could
be messy.

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