[patch] libstdc++/69945 Add __gnu_cxx::__freeres hook

[Jonathan Wakely <jwakely at redhat dot com>]

This adds a new function to libsupc++ which will free the memory still
in use by the pool used for allocating exceptions when malloc fails.

This is similar to glibc's __libc_freeres, which valgrind (and other
tools?) use to tell glibc to deallocate everything before exiting.

I initially called it __gnu_cxx::__free_eh_pool() but I figured we
might have other memory in use at some later date, and we wouldn't
want valgrind to have to start calling a second function, nor make a
function called __free_eh_pool() actually free other things.

I intentionally *didn't* lock the pool's mutex before freeing it,
because this should never be called in a context where multiple
threads are still active and accessing the pool.

Thoughts?

Is the new test a good idea, or will exposing it like that in the
testsuite just give users the idea that they can/should be doing the
same themselves?


[ Aside: should the actual pool be created with placement-new to
[ ensure it doesn't ever get destroyed?
[
[   alignas(pool) unsigned char poolbuf[sizeof(pool)];
[   pool& emergency_pool = *::new(poolbuf) pool;



commit 40fed1db72b0a4852d5890c2c464a0baabb02b74
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Feb 24 18:22:30 2016 +0000

    libstdc++/69945 Add __gnu_cxx::__freeres hook
    
    	* config/abi/pre/gnu.ver: Add new symbol.
    	* libsupc++/eh_alloc.cc (__gnu_cxx::__freeres): Define.
    	* testsuite/18_support/free_eh_pool.cc: New test.

diff --git a/libstdc++-v3/config/abi/pre/gnu.ver b/libstdc++-v3/config/abi/pre/gnu.ver
index 41069d1..5c6b0fe 100644
--- a/libstdc++-v3/config/abi/pre/gnu.ver
+++ b/libstdc++-v3/config/abi/pre/gnu.ver
@@ -2148,6 +2148,8 @@ CXXABI_1.3.10 {
     _ZGTtNKSt13bad_exceptionD1Ev;
     _ZGTtNKSt13bad_exception4whatEv;
 
+    _ZN9__gnu_cxx9__freeresEv;
+
 } CXXABI_1.3.9;
 
 # Symbols in the support library (libsupc++) supporting transactional memory.
diff --git a/libstdc++-v3/libsupc++/eh_alloc.cc b/libstdc++-v3/libsupc++/eh_alloc.cc
index 6973af3..d362e40 100644
--- a/libstdc++-v3/libsupc++/eh_alloc.cc
+++ b/libstdc++-v3/libsupc++/eh_alloc.cc
@@ -73,6 +73,10 @@ using namespace __cxxabiv1;
 # define EMERGENCY_OBJ_COUNT	4
 #endif
 
+namespace __gnu_cxx
+{
+  void __freeres();
+}
 
 namespace
 {
@@ -106,6 +110,8 @@ namespace
       // to implement in_pool.
       char *arena;
       std::size_t arena_size;
+
+      friend void __gnu_cxx::__freeres();
     };
 
   pool::pool()
@@ -244,6 +250,19 @@ namespace
   pool emergency_pool;
 }
 
+namespace __gnu_cxx
+{
+  void
+  __freeres()
+  {
+    if (emergency_pool.arena)
+      {
+	::free(emergency_pool.arena);
+	emergency_pool.arena = 0;
+      }
+  }
+}
+
 extern "C" void *
 __cxxabiv1::__cxa_allocate_exception(std::size_t thrown_size) _GLIBCXX_NOTHROW
 {
diff --git a/libstdc++-v3/testsuite/18_support/free_eh_pool.cc b/libstdc++-v3/testsuite/18_support/free_eh_pool.cc
new file mode 100644
index 0000000..9712d3d
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/free_eh_pool.cc
@@ -0,0 +1,35 @@
+// Copyright (C) 2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do run }
+
+namespace __gnu_cxx {
+  void __freeres();
+}
+
+struct X {
+  ~X() {
+    __gnu_cxx::__freeres();
+  }
+};
+
+X x;
+
+int
+main()
+{
+}