[Bug libstdc++/46332] New: __cxa_demangle yields excess parentheses for function types

[Bug libstdc++/46332] New: __cxa_demangle yields excess parentheses for function types

[gcc-bugzilla at contacts dot eelis.net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

           Summary: __cxa_demangle yields excess parentheses for function
                    types
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: gcc-bugzilla@contacts.eelis.net


Consider:

  #include <iostream>
  #include <typeinfo>
  #include <cxxabi.h>

  int main()
  {
    std::cout <<
     abi::__cxa_demangle(typeid( void() ).name(), 0, 0, 0) << '\n';
  }

The output is "void ()()", but it should really just be "void ()". If "void
()()" had any meaning at all, it would denote the type of a function returning
a function, but of course that's not valid C++.

The same problem can also be seen by trying to compile and link the following
program:

  template <typename> void f();
  int main() { f<void()>(); }

This produces:

  undefined reference to `void f<void ()()>()'

Here, too, "void ()()" is wrong and should just be "void ()".

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ian at airs dot com
          Component|libstdc++                   |other

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2010-11-07 11:08:40 UTC ---
Ian, can you have a look? Thanks in advance.

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2010-11-09 17:02:21 UTC ---
Actually, if this happens also in error messages cannot be a demangler issue
only. I'm pretty sure to have seen this behavior mentioned already... Ian, any
hint?

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[gcc-bugzilla at contacts dot eelis.net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

--- Comment #3 from Eelis <gcc-bugzilla at contacts dot eelis.net> 2010-11-09 17:26:40 UTC ---
(In reply to comment #2)
> I'm pretty sure to have seen this behavior mentioned already...

You may be thinking of bug #36002. That one was about errors emitted during
compilation, and has been fixed. This time it's about errors emitted during
linking (and demangling explicitly). :)

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |paolo.carlini at oracle dot
                   |                            |com

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2010-11-09 18:07:08 UTC ---
Ah, ok, now I notice the linker is involved, thanks for emphasizing that and
the fixed PR. Well, basing on that PR, this one should be fixable pretty
easily!

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2010-11-09 18:09:54 UTC ---
HJ, can you help us figuring out which specific patch fixed 36002? Then I can
work on applying the same tweak to the demangler...

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[ian at airs dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

Ian Lance Taylor <ian at airs dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2010.11.09 19:53:18
                 CC|                            |bkoz at redhat dot com
         AssignedTo|unassigned at gcc dot       |ian at airs dot com
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #6 from Ian Lance Taylor <ian at airs dot com> 2010-11-09 19:53:18 UTC ---
I have a patch for this, but it breaks the libstdc++ test
testsuite/abi/demangle/abi_examples/14.cc .  That test expects _Z3fooIiFvdEiEvv
to demangle to "void foo<int, void ()(double), int>()".  With my patch it
demangles to "void foo<int, void (double), int>()".  That is, the inner "()"
goes away.  Now, clearly the inner "()" makes little sense, but I wonder
whether it should be "(*)" instead.

Ben, you added the test on 2003-02-27.  The test says it comes from the ABI
doc, but I can't find anything in the ABI doc which looks quite like this case.
 Do you recall anything about this test?  Do you think simply omitting the
inner "()" would be an appropriate demangling?

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> 2010-11-09 19:55:49 UTC ---
Thanks.

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[ian at airs dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

--- Comment #7 from Ian Lance Taylor <ian at airs dot com> 2010-11-09 19:55:05 UTC ---
Created attachment 22352
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22352
Possible patch

This is the patch I tested which drops the inner "()".

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |UNCONFIRMED
     Ever Confirmed|1                           |0

--- Comment #9 from H.J. Lu <hjl.tools at gmail dot com> 2010-11-09 19:57:47 UTC ---
(In reply to comment #5)
> HJ, can you help us figuring out which specific patch fixed 36002? Then I can
> work on applying the same tweak to the demangler...


It was fixed by revision 145365:

http://gcc.gnu.org/ml/gcc-cvs/2009-03/msg00872.html

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[bkoz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

Benjamin Kosnik <bkoz at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bkoz at gcc dot gnu.org

--- Comment #10 from Benjamin Kosnik <bkoz at gcc dot gnu.org> 2010-11-09 23:00:30 UTC ---

Hey Ian. I believe this comes from:

http://www.codesourcery.com/public/cxx-abi/abi-examples.html#mangling

But this looks to be slightly different from what is on the table now, ie:

_Z3fooIiPFidEiEvv     void foo<int,int(*)(double),int>();
(Note: return type encoded for template function.)

>From that, I see the (*) is the approved demangling. That does seem to be
better to me than just removing the ().

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[ian at airs dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

Ian Lance Taylor <ian at airs dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|2010-11-09 19:53:18         |2010.11.10 05:17:05
     Ever Confirmed|0                           |1

--- Comment #11 from Ian Lance Taylor <ian at airs dot com> 2010-11-10 05:17:05 UTC ---
I agree that for _Z3fooIiPFidEiEvv we should use (*), and in fact we do use
(*), with or without the patch attached to this PR.  This PR is about a
different sort of symbol, _Z3fooIiFvdEiEvv, or, in the current 14.cc,
_Z3fooIiFvdEiEvv.  The key difference here is that these symbols use F rather
than PF, which means that refer to a function type rather than a pointer to a
function type.  I'm not sure exactly what it means to instantiate a template
with a function type, but g++ does generate these sort of symbols.  I could
change the () to (*), but that would imply a pointer to a function type which
isn't what we have.

So my question for Ben is: should we change the expected demangling in 14.cc to
be void foo<int, void (double), int>() or should we do something else.

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

--- Comment #12 from Paolo Carlini <paolo.carlini at oracle dot com> 2010-11-10 08:24:59 UTC ---
IMHO, void (double) is fine for a function type: Ian's point about function
type vs pointer to function type fully clarifies the issue for me. If currently
the C++ front-end also uses 'void (double)' in error messages, consistency
would be an additional reason.

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[bkoz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

--- Comment #13 from Benjamin Kosnik <bkoz at gcc dot gnu.org> 2010-11-10 15:24:28 UTC ---

> Should we change the expected demangling in 14.cc to
> be void foo<int, void (double), int>() or should we do something else.

I think 14.cc should be foo<int, void (double), int>(). Your change is ok with
me.

FWIW, this is also consistent to C++ hackers using C++0x's std::function
notation. So, at least we are consistent with that (as well as g++ error
messages as pointed out by Paolo.)

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

--- Comment #14 from Jonathan Wakely <redi at gcc dot gnu.org> 2010-11-10 16:46:17 UTC ---
Yep, looks right to me
void (double) is a function type
void (*)(double) is a pointer to such a function type
void (&)(double) is a reference to such a type

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[ian at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

--- Comment #15 from ian at gcc dot gnu.org <ian at gcc dot gnu.org> 2010-11-13 01:21:17 UTC ---
Author: ian
Date: Sat Nov 13 01:21:12 2010
New Revision: 166695

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=166695
Log:
libiberty/:
    PR other/46332
    * cp-demangle.c (d_print_function_type): Don't print parentheses
    if there are no modifiers to print.
    * testsuite/demangle-expected: Tweak one test case, add another.
libstdc++/:
    * testsuite/abi/demangle/abi_examples/14.cc (main): Change
    expected demangling.

Modified:
    trunk/libiberty/ChangeLog
    trunk/libiberty/cp-demangle.c
    trunk/libiberty/testsuite/demangle-expected
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/testsuite/abi/demangle/abi_examples/14.cc

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[ian at airs dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

Ian Lance Taylor <ian at airs dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #16 from Ian Lance Taylor <ian at airs dot com> 2010-11-13 01:24:20 UTC ---
Fixed in mainline.  Thanks for reporting the problem.

In practice the real fix is going to be in the GNU binutils, since that is the
demangler code seen by most people.  I will get this patch into the next GNU
binutils release.

[Bug other/46332] __cxa_demangle yields excess parentheses for function types

[ian at airs dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46332

--- Comment #17 from Ian Lance Taylor <ian at airs dot com> 2010-11-16 14:51:44 UTC ---
I have added this patch to the binutils 2.21 release branch, so it will be in
the GNU binutils 2.21 release.