Bug 1724830 - Use _GLIBCXX_RELEASE in stdc++compat.cpp. r=firefox-build-system-reviewers,andi

Since the minimum required version of gcc and libstdc++ is 7.1 as of bug
1536848, the _GLIBCXX_RELEASE macro is available on all supported
versions. Which means instead of grabbing the largest version of the
libstdc++ symbols and tweaking for that, we can just tweak for
_GLIBCXX_RELEASE. We also remove the conditions that are always true due
to the versions involved.

Differential Revision: https://phabricator.services.mozilla.com/D122194

build/unix/stdc++compat/moz.build

@@ -21,7 +21,4 @@ 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]

build/unix/stdc++compat/stdc++compat.cpp

@@ -33,13 +33,11 @@ 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, 20)
 namespace std {
 
 /* We shouldn't be throwing exceptions at all, but it sadly turns out
-   we call STL (inline) functions that do. */
+   we call STL (inline) functions that do. This avoids the GLIBCXX_3.4.20
+   symbol version. */
 void __attribute__((weak)) __throw_out_of_range_fmt(char const* fmt, ...) {
   va_list ap;
   char buf[1024];  // That should be big enough.
@@ -53,42 +51,36 @@ void __attribute__((weak)) __throw_out_of_range_fmt(char const* fmt, ...) {
 }
 
 }  // namespace std
-#endif
 
-#if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 20)
 namespace __cxxabiv1 {
-/* 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. */
+/* Calls to this function are added by the compiler itself on `new Class[n]`
+ * calls. This avoids the GLIBCXX_3.4.20 symbol version. */
 extern "C" void __attribute__((weak)) __cxa_throw_bad_array_new_length() {
   MOZ_CRASH();
 }
 }  // namespace __cxxabiv1
-#endif
 
-#if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 29)
+#if _GLIBCXX_RELEASE >= 11
 namespace std {
 
+/* This avoids the GLIBCXX_3.4.29 symbol version. */
 void __attribute__((weak)) __throw_bad_array_new_length() { MOZ_CRASH(); }
 
 }  // namespace std
 #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. */
+ * std::string. This avoids the GLIBCXX_3.4.21 symbol version. */
 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>
+#define _GLIBCXX_THREAD_ABI_COMPAT 1
+#include <thread>
 
 namespace std {
 /* The old ABI has a thread::_M_start_thread(shared_ptr<_Impl_base>),
@@ -98,16 +90,15 @@ namespace std {
  * 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. */
-
+ * them call the old ABI. This avoids the GLIBCXX_3.4.21 symbol version. */
 __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 */
+ * from what we got by diverting the new API. This avoids the GLIBCXX_3.4.22
+ * symbol version. */
 struct StateWrapper : public thread::_Impl_base {
   unique_ptr<thread::_State> mState;
 
@@ -116,6 +107,7 @@ struct StateWrapper : public thread::_Impl_base {
   void _M_run() override { mState->_M_run(); }
 };
 
+/* This avoids the GLIBCXX_3.4.22 symbol version. */
 __attribute__((weak)) void thread::_M_start_thread(unique_ptr<_State> aState,
                                                    void (*)()) {
   auto impl = std::make_shared<StateWrapper>(std::move(aState));
@@ -123,11 +115,11 @@ __attribute__((weak)) void thread::_M_start_thread(unique_ptr<_State> aState,
 }
 
 /* For some reason this is a symbol exported by new versions of libstdc++,
- * even though the destructor is default there too */
+ * even though the destructor is default there too. This avoids the
+ * GLIBCXX_3.4.22 symbol version. */
 __attribute__((weak)) thread::_State::~_State() = default;
-#  endif
 
-#  if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 26)
+#if _GLIBCXX_RELEASE >= 9
 // Ideally we'd define
 //    bool _Sp_make_shared_tag::_S_eq(const type_info& ti) noexcept
 // but we wouldn't be able to change its visibility because of the existing
@@ -136,55 +128,53 @@ __attribute__((weak)) thread::_State::~_State() = default;
 // it doesn't support RTTI. Not supporting RTTI doesn't matter for Firefox
 // itself because it's built with RTTI disabled.
 // So we define via the mangled symbol.
+// This avoids the GLIBCXX_3.4.26 symbol version.
 extern "C" __attribute__((visibility("hidden"))) bool
 _ZNSt19_Sp_make_shared_tag5_S_eqERKSt9type_info(const type_info*) noexcept {
   return false;
 }
-#  endif
-
-}  // namespace std
 #endif
 
-#if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 21)
+}  // namespace std
+
 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)
+#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>&);
 
-#  if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 26)
+#if _GLIBCXX_RELEASE >= 9
+// This avoids the GLIBCXX_3.4.26 symbol version.
 template basic_stringstream<char, char_traits<char>,
                             allocator<char>>::basic_stringstream();
 
 template basic_ostringstream<char, char_traits<char>,
                              allocator<char>>::basic_ostringstream();
-#  endif
+#endif
 
-#  if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 29)
+#if _GLIBCXX_RELEASE >= 11
+// This avoids the GLIBCXX_3.4.29 symbol version.
 template void basic_string<char, char_traits<char>, allocator<char>>::reserve();
 
 template void
 basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t>>::reserve();
-#  endif
+#endif
 
 }  // 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