diff --git a/build/unix/stdc++compat/stdc++compat.cpp b/build/unix/stdc++compat/stdc++compat.cpp
index 5ce33346c17d..d8637042ae74 100644
--- a/build/unix/stdc++compat/stdc++compat.cpp
+++ b/build/unix/stdc++compat/stdc++compat.cpp
@@ -8,7 +8,6 @@
 #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)
@@ -145,12 +144,6 @@ namespace std {
  * depending on optimization level */
 template basic_ios<char, char_traits<char>>::operator bool() const;
 }  // namespace std
-
-/* 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
 
 #if MOZ_LIBSTDCXX_VERSION >= GLIBCXX_VERSION(3, 4, 23)
@@ -161,18 +154,3 @@ 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);
-}
diff --git a/python/mozbuild/mozbuild/action/check_binary.py b/python/mozbuild/mozbuild/action/check_binary.py
index 57ccfa6b29df..1b69b8bcd3d2 100644
--- a/python/mozbuild/mozbuild/action/check_binary.py
+++ b/python/mozbuild/mozbuild/action/check_binary.py
@@ -23,7 +23,6 @@ from mozpack.executables import (
 
 
 STDCXX_MAX_VERSION = Version('3.4.19')
-CXXABI_MAX_VERSION = Version('1.3.7')
 GLIBC_MAX_VERSION = Version('2.17')
 LIBGCC_MAX_VERSION = Version('4.8')
 
@@ -97,8 +96,11 @@ def iter_symbols(binary):
                 continue
             addr = int(m.group(0), 16)
             # The second "column" is 7 one-character items that can be
-            # whitespaces. We don't have use for their value, so just skip
-            # those.
+            # whitespaces.
+            flags = line[m.end():][:7]
+            # We're only interested whether the symbol might be weak.
+            weak = 'w' in flags
+
             rest = line[m.end() + 9:].split()
             # The number of remaining colums will vary between ELF and MACHO.
             # On ELF, we have:
@@ -117,6 +119,7 @@ def iter_symbols(binary):
                 'size': int(rest[1], 16) if ty == ELF else 0,
                 'name': name,
                 'version': ver or None,
+                'weak': weak,
             }
     else:
         export_table = False
@@ -144,6 +147,7 @@ def iter_symbols(binary):
                 'size': 0,
                 'name': name,
                 'version': None,
+                'weak': None,
             }
 
 
@@ -165,6 +169,11 @@ def check_dep_versions(target, binary, lib, prefix, max_version):
             if sym['addr'] != 0:
                 continue
 
+            # Versions for weak symbols don't matter, since the code must
+            # handle the case where they're not defined.
+            if sym['weak']:
+                continue
+
             # No version to check
             if not sym['version']:
                 continue
@@ -186,8 +195,6 @@ def check_dep_versions(target, binary, lib, prefix, max_version):
 def check_stdcxx(target, binary):
     check_dep_versions(
         target, binary, 'libstdc++', 'GLIBCXX', STDCXX_MAX_VERSION)
-    check_dep_versions(
-        target, binary, 'libstdc++', 'CXXABI', CXXABI_MAX_VERSION)
 
 
 def check_libgcc(target, binary):