Re: ../../gdbsupport/new-op.cc:137:1: error: ‘void operator delete [](void*, std::size_t)’ is a usual (non-placement) deallocation function in C++14 (or with -fsized-deallocation) [-Werror=c++14-compat]

[Andrew Burgess <aburgess@redhat.com>]

* 周春明(日月) via Gdb-patches <gdb-patches@sourceware.org> [2022-03-01 15:48:47 +0800]:

> 
> Hi GDB maintainers,
> 
> I tried to build new GDB12, but encounter below error, anyone could tell me how to fix it? Thanks!
> 
>  CXX new-op.o
> ../../gdbsupport/new-op.cc:32:13: error: ‘void operator delete(void*, std::size_t)’ is a usual (non-placement) deallocation function in C++14 (or with -fsized-deallocation) [-Werror=c++14-compat]
>  extern void operator delete (void *p, std::size_t) noexcept;
>  ^
> ../../gdbsupport/new-op.cc:33:13: error: ‘void operator delete [](void*, std::size_t)’ is a usual (non-placement) deallocation function in C++14 (or with -fsized-deallocation) [-Werror=c++14-compat]
>  extern void operator delete[] (void *p, std::size_t) noexcept;
>  ^
> ../../gdbsupport/new-op.cc:119:1: error: ‘void operator delete(void*, std::size_t)’ is a usual (non-placement) deallocation function in C++14 (or with -fsized-deallocation) [-Werror=c++14-compat]
>  operator delete (void *p, std::size_t) noexcept
>  ^
> ../../gdbsupport/new-op.cc:137:1: error: ‘void operator delete [](void*, std::size_t)’ is a usual (non-placement) deallocation function in C++14 (or with -fsized-deallocation) [-Werror=c++14-compat]
>  operator delete[] (void *p, std::size_t) noexcept

I was able to reproduce this on Ubuntu 16.04.1 with their gcc 5.4.0.
I was unable to easily rebuild GCC 5.4.0 on my current development
machine to check if this is reproducible with upstream gcc, or is just
something impacting Ubuntu.  However, you can configure like:

  ../src/configure ...configure-flags-here... CXXFLAGS="-Wno-error=c++14-compat"

to disable this warning/error which I believe should be fine.

For why this error is occurring, I'm honestly not 100% sure what the
error is telling us.  I _think_ what it's saying is that the delete
operator that we're declaring/defining conflicts with a "usual
deallocation function", which is added in c++14 and means something
specific.  I guess the idea is that maybe we're just randomly defining
this version of delete for some reason, and then, if/when we move on
to c++14 this function will get called unexpectedly by the language
runtime in some situations.

As time moved on I think this warning was relaxed, possibly with this
commit:

  https://gcc.gnu.org/legacy-ml/gcc-patches/2015-05/msg01883.html

All this makes me wonder if the usual deallocation functions are ever
actually used, and indeed, I applied the patch below, and GDB still
seems to build fine, so this might be an alternative approach.  Maybe
we should commit this to master?

Thanks,
Andrew

---

diff --git a/gdbsupport/new-op.cc b/gdbsupport/new-op.cc
index 1d066ba..4faa557 100644
--- a/gdbsupport/new-op.cc
+++ b/gdbsupport/new-op.cc
@@ -27,11 +27,6 @@
 #include "host-defs.h"
 #include <new>
 
-/* These are declared in <new> starting C++14.  Add these here to enable
-   compilation using C++11. */
-extern void operator delete (void *p, std::size_t) noexcept;
-extern void operator delete[] (void *p, std::size_t) noexcept;
-
 /* Override operator new / operator new[], in order to internal_error
    on allocation failure and thus query the user for abort/core
    dump/continue, just like xmalloc does.  We don't do this from a
@@ -116,12 +111,6 @@ operator delete (void *p, const std::nothrow_t&) noexcept
 }
 
 void
-operator delete (void *p, std::size_t) noexcept
-{
-  return ::operator delete (p, std::nothrow);
-}
-
-void
 operator delete[] (void *p) noexcept
 {
   return ::operator delete (p);
@@ -133,10 +122,4 @@ operator delete[] (void *p, const std::nothrow_t&) noexcept
   return ::operator delete (p, std::nothrow);
 }
 
-void
-operator delete[] (void *p, std::size_t) noexcept
-{
-  return ::operator delete[] (p, std::nothrow);
-}
-
 #endif