3 files changed, 212 insertions, 0 deletions
diff --git a/build/unix/stdc++compat/hide_std.ld b/build/unix/stdc++compat/hide_std.ld
new file mode 100644
index 0000000000..4b3400b0f3
--- /dev/null
+++ b/build/unix/stdc++compat/hide_std.ld
@@ -0,0 +1,5 @@
+hidden {
+  local:
+    # std::thread::_M_start_thread(...)
+    _ZNSt6thread15_M_start_thread*;
+};
diff --git a/build/unix/stdc++compat/moz.build b/build/unix/stdc++compat/moz.build
new file mode 100644
index 0000000000..aac8f2b0f5
--- /dev/null
+++ b/build/unix/stdc++compat/moz.build
@@ -0,0 +1,27 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+if CONFIG["MOZ_LIBSTDCXX_TARGET_VERSION"]:
+    Library("stdc++compat")
+    SOURCES += ["stdc++compat.cpp"]
+
+if CONFIG["MOZ_LIBSTDCXX_HOST_VERSION"]:
+    HostLibrary("host_stdc++compat")
+    HOST_SOURCES += [
+        "stdc++compat.cpp",
+    ]
+
+FORCE_STATIC_LIB = True
+
+NO_PGO = True
+
+DisableStlWrapping()
+COMPILE_FLAGS["CLANG_PLUGIN"] = []
+
+DEFINES["MOZ_LIBSTDCXX_VERSION"] = CONFIG["MOZ_LIBSTDCXX_TARGET_VERSION"]
+HOST_DEFINES["MOZ_LIBSTDCXX_VERSION"] = CONFIG["MOZ_LIBSTDCXX_HOST_VERSION"]
+
+OS_LIBS += ["-Wl,--version-script,%s/hide_std.ld" % SRCDIR]
diff --git a/build/unix/stdc++compat/stdc++compat.cpp b/build/unix/stdc++compat/stdc++compat.cpp
new file mode 100644
index 0000000000..1d12ea7744
--- /dev/null
+++ b/build/unix/stdc++compat/stdc++compat.cpp
@@ -0,0 +1,180 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <ostream>
+#include <istream>
+#include <string>
+#include <stdarg.h>
+#include <stdio.h>
+#include <mozilla/Assertions.h>
+#include <cxxabi.h>
+
+/* GLIBCXX_3.4.16 is from gcc 4.6.1 (172240)
+   GLIBCXX_3.4.17 is from gcc 4.7.0 (174383)
+   GLIBCXX_3.4.18 is from gcc 4.8.0 (190787)
+   GLIBCXX_3.4.19 is from gcc 4.8.1 (199309)
+   GLIBCXX_3.4.20 is from gcc 4.9.0 (199307)
+   GLIBCXX_3.4.21 is from gcc 5.0 (210290)
+   GLIBCXX_3.4.22 is from gcc 6.0 (222482)
+   GLIBCXX_3.4.23 is from gcc 7.0
+
+This file adds the necessary compatibility tricks to avoid symbols with
+version GLIBCXX_3.4.17 and bigger, keeping binary compatibility with
+libstdc++ 4.7.
+
+WARNING: all symbols from this file must be defined weak when they
+overlap with libstdc++.
+*/
+
+#define GLIBCXX_VERSION(a, b, c) (((a) << 16) | ((b) << 8) | (c))
+
+#if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 18)
+// Implementation of utility functions for the prime rehash policy used in
+// unordered_map and unordered_set.
+#  include <unordered_map>
+#  include <tr1/unordered_map>
+namespace std {
+size_t __attribute__((weak))
+__detail::_Prime_rehash_policy::_M_next_bkt(size_t __n) const {
+  tr1::__detail::_Prime_rehash_policy policy(_M_max_load_factor);
+  size_t ret = policy._M_next_bkt(__n);
+  _M_next_resize = policy._M_next_resize;
+  return ret;
+}
+
+pair<bool, size_t> __attribute__((weak))
+__detail::_Prime_rehash_policy::_M_need_rehash(size_t __n_bkt, size_t __n_elt,
+                                               size_t __n_ins) const {
+  tr1::__detail::_Prime_rehash_policy policy(_M_max_load_factor);
+  policy._M_next_resize = _M_next_resize;
+  pair<bool, size_t> ret = policy._M_need_rehash(__n_bkt, __n_elt, __n_ins);
+  _M_next_resize = policy._M_next_resize;
+  return ret;
+}
+}  // namespace std
+#endif
+
+#if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 20)
+namespace std {
+
+/* We shouldn't be throwing exceptions at all, but it sadly turns out
+   we call STL (inline) functions that do. */
+void __attribute__((weak)) __throw_out_of_range_fmt(char const* fmt, ...) {
+  va_list ap;
+  char buf[1024];  // That should be big enough.
+
+  va_start(ap, fmt);
+  vsnprintf(buf, sizeof(buf), fmt, ap);
+  buf[sizeof(buf) - 1] = 0;
+  va_end(ap);
+
+  __throw_range_error(buf);
+}
+
+}  // namespace std
+#endif
+
+#if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 20)
+/* Technically, this symbol is not in GLIBCXX_3.4.20, but in CXXABI_1.3.8,
+   but that's equivalent, version-wise. Those calls are added by the compiler
+   itself on `new Class[n]` calls. */
+extern "C" void __attribute__((weak)) __cxa_throw_bad_array_new_length() {
+  MOZ_CRASH();
+}
+#endif
+
+#if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 21)
+/* While we generally don't build with exceptions, we have some host tools
+ * that do use them. libstdc++ from GCC 5.0 added exception constructors with
+ * char const* argument. Older versions only have a constructor with
+ * std::string. */
+namespace std {
+__attribute__((weak)) runtime_error::runtime_error(char const* s)
+    : runtime_error(std::string(s)) {}
+}  // namespace std
+#endif
+
+#if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 21)
+/* Expose the definitions for the old ABI, allowing us to call its functions */
+#  define _GLIBCXX_THREAD_ABI_COMPAT 1
+#  include <thread>
+
+namespace std {
+/* The old ABI has a thread::_M_start_thread(shared_ptr<_Impl_base>),
+ * while the new has thread::_M_start_thread(unique_ptr<_State>, void(*)()).
+ * There is an intermediate ABI at version 3.4.21, with
+ * thread::_M_start_thread(shared_ptr<_Impl_base>, void(*)()).
+ * The void(*)() parameter is only there to keep a reference to pthread_create
+ * on the caller side, and is unused in the implementation
+ * We're creating an entry point for the new and intermediate ABIs, and make
+ * them call the old ABI. */
+
+__attribute__((weak)) void thread::_M_start_thread(shared_ptr<_Impl_base> impl,
+                                                   void (*)()) {
+  _M_start_thread(std::move(impl));
+}
+
+#  if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 22)
+/* We need a _Impl_base-derived class wrapping a _State to call the old ABI
+ * from what we got by diverting the new API */
+struct StateWrapper : public thread::_Impl_base {
+  unique_ptr<thread::_State> mState;
+
+  StateWrapper(unique_ptr<thread::_State> aState) : mState(std::move(aState)) {}
+
+  void _M_run() override { mState->_M_run(); }
+};
+
+__attribute__((weak)) void thread::_M_start_thread(unique_ptr<_State> aState,
+                                                   void (*)()) {
+  auto impl = std::make_shared<StateWrapper>(std::move(aState));
+  _M_start_thread(std::move(impl));
+}
+
+/* For some reason this is a symbol exported by new versions of libstdc++,
+ * even though the destructor is default there too */
+__attribute__((weak)) thread::_State::~_State() = default;
+#  endif
+}  // namespace std
+#endif
+
+#if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 21)
+namespace std {
+/* Instantiate this template to avoid GLIBCXX_3.4.21 symbol versions
+ * depending on optimization level */
+template basic_ios<char, char_traits<char>>::operator bool() const;
+}  // namespace std
+
+#  if !defined(MOZ_ASAN) && !defined(MOZ_TSAN)
+/* operator delete with size is only available in CXXAPI_1.3.9, equivalent to
+ * GLIBCXX_3.4.21. */
+void operator delete(void* ptr, size_t size) noexcept(true) {
+  ::operator delete(ptr);
+}
+#  endif
+#endif
+
+#if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 23)
+namespace std {
+/* Instantiate this template to avoid GLIBCXX_3.4.23 symbol versions
+ * depending on optimization level */
+template basic_string<char, char_traits<char>, allocator<char>>::basic_string(
+    const basic_string&, size_t, const allocator<char>&);
+}  // namespace std
+#endif
+
+/* The __cxa_thread_atexit_impl symbol is only available on GLIBC 2.18, but we
+ * want things to keep working on 2.17. It's not actually used directly from
+ * C++ code, but through __cxa_thead_atexit in libstdc++. The problem we have,
+ * though, is that rust's libstd also uses it, introducing a dependency we
+ * don't actually want. Fortunately, we can fall back to libstdc++'s wrapper
+ * (which, on systems without __cxa_thread_atexit_impl, has its own compatible
+ * implementation).
+ * The __cxa_thread_atexit symbol itself is marked CXXABI_1.3.7, which is
+ * equivalent to GLIBCXX_3.4.18.
+ */
+extern "C" int __cxa_thread_atexit_impl(void (*dtor)(void*), void* obj,
+                                        void* dso_handle) {
+  return __cxxabiv1::__cxa_thread_atexit(dtor, obj, dso_handle);
+}