Bug 1464084 - Don't export std:🧵:_M_start_thread symbols with --enable-stdcxx-compat. r=froydnj

This relies on the fact that providing multiple --version-script
combines them all, so we effectively create a new symbol version
that has no global symbol, but hides the std:🧵:_M_start_thread
symbols.

This version script trick happens to work with BFD ld, gold, and lld.

The downside is that when providing multiple --version-script's, ld
doesn't want any of them to have no version at all. So for the libraries
that do already have a version script (through SYMBOLS_FILE), we use a
version where there used to be none, using the library name as the
version. Practically speaking, this binds the libraries a little closer
than they used to be, kind of non-flat namespace on OSX (which is the
default there), meaning the dynamic linker will actively want to use
symbols from those libraries instead of a system library that might
happen to have the same symbol name.

--HG--
extra : rebase_source : a7f672c35609d993849385ddb874ba791b34f929

build/unix/stdc++compat/hide_std.ld

@@ -0,0 +1,5 @@
+hidden {
+  local:
+    # std::thread::_M_start_thread(...)
+    _ZNSt6thread15_M_start_thread*;
+};

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

@@ -23,3 +23,5 @@ 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]

python/mozbuild/mozbuild/action/generate_symbols_file.py

@@ -42,6 +42,8 @@ def generate_symbols_file(output, *args):
 
     symbols = [s.strip() for s in pp.out.getvalue().splitlines() if s.strip()]
 
+    libname, ext = os.path.splitext(os.path.basename(output.name))
+
     if buildconfig.substs['OS_TARGET'] == 'WINNT':
         # A def file is generated for MSVC link.exe that looks like the
         # following:
@@ -66,14 +68,13 @@ def generate_symbols_file(output, *args):
         # those platforms, and to DATA on Windows, so that the "DATA" part
         # is, in fact, part of the symbol name as far as the symbols variable
         # is concerned.
-        libname, ext = os.path.splitext(os.path.basename(output.name))
         assert ext == '.def'
         output.write('LIBRARY %s\nEXPORTS\n  %s\n'
                      % (libname, '\n  '.join(symbols)))
     elif buildconfig.substs['GCC_USE_GNU_LD']:
         # A linker version script is generated for GNU LD that looks like the
         # following:
-        # {
+        # liblibrary.so {
         # global:
         #   symbol1;
         #   symbol2;
@@ -81,8 +82,8 @@ def generate_symbols_file(output, *args):
         # local:
         #   *;
         # };
-        output.write('{\nglobal:\n  %s;\nlocal:\n  *;\n};'
-                     % ';\n  '.join(symbols))
+        output.write('%s {\nglobal:\n  %s;\nlocal:\n  *;\n};'
+                     % (libname, ';\n  '.join(symbols)))
     elif buildconfig.substs['OS_TARGET'] == 'Darwin':
         # A list of symbols is generated for Apple ld that simply lists all
         # symbols, with an underscore prefix.

testing/cppunittest.ini

@@ -43,7 +43,6 @@ skip-if = os == 'android' # Bug 1147630
 [TestSaturate]
 [TestSplayTree]
 [TestSPSCQueue]
-skip-if = os == 'linux' # Bug 1464084
 [TestSyncRunnable]
 [TestTemplateLib]
 [TestTuple]