Build shared libraries by default with -shared

The old behavior was to build fake/dummy shared libraries which were
really just normal object files.  This old behavior can still achieved
by settings the new `FAKE_DYLIBS` settings.

Author: sbc100

cmake/Modules/Platform/Emscripten.cmake

@@ -18,7 +18,7 @@ set(CMAKE_SYSTEM_NAME Emscripten)
 set(CMAKE_SYSTEM_VERSION 1)
 
 set(CMAKE_CROSSCOMPILING TRUE)
-set_property(GLOBAL PROPERTY TARGET_SUPPORTS_SHARED_LIBS FALSE)
+set_property(GLOBAL PROPERTY TARGET_SUPPORTS_SHARED_LIBS TRUE)
 
 # Advertise Emscripten as a 32-bit platform (as opposed to
 # CMAKE_SYSTEM_PROCESSOR=x86_64 for 64-bit platform), since some projects (e.g.

src/settings.js

@@ -2230,3 +2230,9 @@ var WASM_JS_TYPES = false;
 // CROSS_ORIGIN uses an inline worker to instead load the worker script
 // indirectly using `importScripts`
 var CROSS_ORIGIN = false;
+
+// This settings changes the behaviour of the ``-shared`` flag.  When set to true
+// you get the old emscripten behaivour where the ``-shared`` flag actually
+// produces a normal object file (i.e. ``ld -r``).  The default behaviour is that
+// `-shared` is the as :ref:`SIDE_MODULE`.
+var FAKE_DYLIBS = false;

test/test_other.py

@@ -1235,10 +1235,10 @@ def test_odd_suffixes(self):
       shutil.copy(test_file('hello_world.c'), 'test.' + suffix)
       self.do_runf('test.' + suffix, 'hello, world!')
 
-    for suffix in ('lo'):
+    for suffix in ('lo',):
       self.clear()
       print(suffix)
-      self.run_process([EMCC, test_file('hello_world.c'), '-shared', '-o', 'binary.' + suffix])
+      self.run_process([EMCC, test_file('hello_world.c'), '-sFAKE_DYLIBS', '-shared', '-o', 'binary.' + suffix])
       self.run_process([EMCC, 'binary.' + suffix])
       self.assertContained('hello, world!', self.run_js('a.out.js'))
 
@@ -1419,7 +1419,7 @@ def test_multiply_defined_libsymbols(self):
     ''')
 
     self.cflags.remove('-Werror')
-    self.emcc('libA.c', ['-shared', '-o', 'libA.so'])
+    self.emcc('libA.c', ['-shared', '-sFAKE_DYLIBS', '-o', 'libA.so'])
 
     self.emcc('a2.c', ['-r', '-L.', '-lA', '-o', 'a2.o'])
     self.emcc('b2.c', ['-r', '-L.', '-lA', '-o', 'b2.o'])
@@ -1552,7 +1552,12 @@ def test_link_group_bitcode(self):
   # We deliberately ignore duplicate input files in order to allow
   # "libA.so" on the command line twice. This is not really .so support
   # and the .so files are really object files.
-  def test_redundant_link(self):
+  @parameterized({
+    '': ([],),
+    'fake_dylibs': (['-sFAKE_DYLIBS'],),
+  })
+  def test_redundant_link(self, args):
+    self.cflags += args
     create_file('libA.c', 'int mult() { return 1; }')
     create_file('main.c', r'''
       #include <stdio.h>
@@ -1564,7 +1569,7 @@ def test_redundant_link(self):
     ''')
 
     self.cflags.remove('-Werror')
-    self.emcc('libA.c', ['-shared', '-o', 'libA.so'])
+    self.emcc('libA.c', ['-fPIC', '-shared', '-o', 'libA.so'])
     self.emcc('main.c', ['libA.so', 'libA.so', '-o', 'a.out.js'])
     self.assertContained('result: 1', self.run_js('a.out.js'))
 
@@ -2159,9 +2164,9 @@ def test_multidynamic_link(self, link_flags, lib_suffix):
     ''')
 
     # Build libfile normally into an .so
-    self.run_process([EMCC, 'libdir/libfile.c', '-shared', '-o', 'libdir/libfile.so' + lib_suffix])
+    self.run_process([EMCC, 'libdir/libfile.c', '-sFAKE_DYLIBS', '-shared', '-fPIC', '-o', 'libdir/libfile.so' + lib_suffix])
     # Build libother and dynamically link it to libfile
-    self.run_process([EMCC, '-Llibdir', 'libdir/libother.c'] + link_flags + ['-shared', '-o', 'libdir/libother.so'])
+    self.run_process([EMCC, '-Llibdir', 'libdir/libother.c'] + link_flags + ['-sFAKE_DYLIBS', '-shared', '-fPIC', '-o', 'libdir/libother.so'])
     # Build the main file, linking in both the libs
     self.run_process([EMCC, '-Llibdir', os.path.join('main.c')] + link_flags + ['-lother', '-c'])
     print('...')
@@ -4906,20 +4911,6 @@ def test_valid_abspath_2(self):
     self.run_process(cmd)
     self.assertContained('hello, world!', self.run_js('a.out.js'))
 
-  def test_warn_dylibs(self):
-    shared_suffixes = ['.so', '.dylib', '.dll']
-
-    for suffix in ('.o', '.bc', '.so', '.dylib', '.js', '.html'):
-      print(suffix)
-      cmd = [EMCC, test_file('hello_world.c'), '-o', 'out' + suffix]
-      if suffix in ['.o', '.bc']:
-        cmd.append('-c')
-      if suffix in ['.dylib', '.so']:
-        cmd.append('-shared')
-      err = self.run_process(cmd, stderr=PIPE).stderr
-      warning = 'linking a library with `-shared` will emit a static object file'
-      self.assertContainedIf(warning, err, suffix in shared_suffixes)
-
   @crossplatform
   @parameterized({
     'O2': [['-O2']],
@@ -8369,20 +8360,6 @@ def test_side_module_folder_deps(self):
     self.run_process([EMCC, test_file('hello_world.c'), '-sSIDE_MODULE', '-o', 'subdir/libside2.so', '-L', 'subdir', '-lside1'])
     self.run_process([EMCC, test_file('hello_world.c'), '-sMAIN_MODULE', '-o', 'main.js', '-L', 'subdir', '-lside2'])
 
-  @crossplatform
-  def test_side_module_ignore(self):
-    self.run_process([EMCC, test_file('hello_world.c'), '-sSIDE_MODULE', '-o', 'libside.so'])
-
-    # Attempting to link statically against a side module (libside.so) should fail.
-    err = self.expect_fail([EMCC, '-L.', '-lside'])
-    self.assertContained(r'error: attempted static link of dynamic object \.[/\\]libside.so', err, regex=True)
-
-    # But a static library in the same location (libside.a) should take precedence.
-    self.run_process([EMCC, test_file('hello_world.c'), '-c'])
-    self.run_process([EMAR, 'cr', 'libside.a', 'hello_world.o'])
-    self.run_process([EMCC, '-L.', '-lside'])
-    self.assertContained('hello, world!', self.run_js('a.out.js'))
-
   @is_slow_test
   @parameterized({
     '': ([],),
@@ -11903,23 +11880,24 @@ def test_err(self):
   def test_euidaccess(self):
     self.do_other_test('test_euidaccess.c')
 
-  def test_shared_flag(self):
-    self.run_process([EMCC, '-shared', test_file('hello_world.c'), '-o', 'libother.so'])
+  def test_fake_dylibs(self):
+    self.run_process([EMCC, '-shared', '-sFAKE_DYLIBS', '-fPIC', test_file('hello_world.c'), '-o', 'libother.so'])
+    self.assertIsObjectFile('libother.so')
 
-    # Test that `-shared` flag causes object file generation but gives a warning
-    err = self.run_process([EMCC, '-shared', test_file('hello_world.c'), '-o', 'out.foo', 'libother.so'], stderr=PIPE).stderr
-    self.assertContained('linking a library with `-shared` will emit a static object', err)
+    # Test that `-sFAKE_DYLIBS` flag causes object file generation and will generate a warning about
+    # dylink dependencies being ignored.
+    err = self.run_process([EMCC, '-shared', '-sFAKE_DYLIBS', '-fPIC', test_file('hello_world.c'), '-o', 'out.foo', 'libother.so'], stderr=PIPE).stderr
     self.assertContained('emcc: warning: ignoring dynamic library libother.so when generating an object file, this will need to be included explicitly in the final link', err)
     self.assertIsObjectFile('out.foo')
 
     # Test that using an executable output name overrides the `-shared` flag, but produces a warning.
-    err = self.run_process([EMCC, '-shared', test_file('hello_world.c'), '-o', 'out.js'],
+    err = self.run_process([EMCC, '-shared', '-sFAKE_DYLIBS', '-fPIC', test_file('hello_world.c'), '-o', 'out.js'],
                            stderr=PIPE).stderr
     self.assertContained('warning: -shared/-r used with executable output suffix', err)
     self.run_js('out.js')
 
   def test_shared_soname(self):
-    self.run_process([EMCC, '-shared', '-Wl,-soname', '-Wl,libfoo.so.13', test_file('hello_world.c'), '-lc', '-o', 'libfoo.so'])
+    self.run_process([EMCC, '-shared', '-sFAKE_DYLIBS', '-Wl,-soname', '-Wl,libfoo.so.13', test_file('hello_world.c'), '-lc', '-o', 'libfoo.so'])
     self.run_process([EMCC, '-sSTRICT', 'libfoo.so'])
     self.assertContained('hello, world!', self.run_js('a.out.js'))
 

tools/building.py

@@ -170,6 +170,9 @@ def lld_flags_for_executable(external_symbols):
     stub = create_stub_object(external_symbols)
     cmd.append(stub)
 
+  if not settings.FAKE_DYLIBS:
+    cmd.append('-Bdynamic')
+
   if not settings.ERROR_ON_UNDEFINED_SYMBOLS:
     cmd.append('--import-undefined')
 

tools/cmdline.py

@@ -65,6 +65,7 @@ class EmccOptions:
   dash_M = False
   dash_S = False
   dash_c = False
+  dylibs: List[str] = []
   embed_files: List[str] = []
   emit_symbol_map = False
   emit_tsd = ''

tools/link.py

@@ -829,6 +829,22 @@ def setup_sanitizers(options):
     settings.LOAD_SOURCE_MAP = 1
 
 
+def get_dylibs(options, linker_args):
+  """Find all the Wasm dynanamic libraries specified on the command line,
+  either via `-lfoo` or vis `libfoo.so` directly."""
+
+  dylibs = []
+  for arg in linker_args:
+    if arg.startswith('-l'):
+      for ext in DYLIB_EXTENSIONS:
+        path = find_library('lib' + arg[2:] + ext, options.lib_dirs)
+        if path and building.is_wasm_dylib(path):
+          dylibs.append(path)
+    elif building.is_wasm_dylib(arg):
+      dylibs.append(arg)
+  return dylibs
+
+
 @ToolchainProfiler.profile_block('linker_setup')
 def phase_linker_setup(options, linker_args):  # noqa: C901, PLR0912, PLR0915
   """Future modifications should consider refactoring to reduce complexity.
@@ -843,6 +859,15 @@ def phase_linker_setup(options, linker_args):  # noqa: C901, PLR0912, PLR0915
   setup_environment_settings()
 
   apply_library_settings(linker_args)
+
+  if options.shared and not settings.FAKE_DYLIBS:
+    default_setting('SIDE_MODULE', 1)
+    default_setting('RELOCATABLE', 1)
+
+  options.dylibs = get_dylibs(options, linker_args)
+  if not settings.MAIN_MODULE and not settings.SIDE_MODULE and options.dylibs:
+    default_setting('MAIN_MODULE', 2)
+
   linker_args += calc_extra_ldflags(options)
 
   # We used to do this check during on startup during `check_sanity`, but
@@ -936,16 +961,12 @@ def phase_linker_setup(options, linker_args):  # noqa: C901, PLR0912, PLR0915
 
   # If no output format was specified we try to deduce the format based on
   # the output filename extension
-  if not options.oformat and (options.relocatable or (options.shared and not settings.SIDE_MODULE)):
-    # Until we have a better story for actually producing runtime shared libraries
-    # we support a compatibility mode where shared libraries are actually just
-    # object files linked with `wasm-ld --relocatable` or `llvm-link` in the case
-    # of LTO.
+  if not options.oformat and (options.relocatable or (options.shared and settings.FAKE_DYLIBS)):
+    # With FAKE_DYLIBS we generate an normal object file rather than an shared object.
+    # This is linked with `wasm-ld --relocatable` or (`llvm-link` in the case of LTO).
     if final_suffix in EXECUTABLE_EXTENSIONS:
       diagnostics.warning('emcc', '-shared/-r used with executable output suffix. This behaviour is deprecated.  Please remove -shared/-r to build an executable or avoid the executable suffix (%s) when building object files.' % final_suffix)
     else:
-      if options.shared:
-        diagnostics.warning('emcc', 'linking a library with `-shared` will emit a static object file.  This is a form of emulation to support existing build systems.  If you want to build a runtime shared library use the SIDE_MODULE setting.')
       options.oformat = OFormat.OBJECT
 
   if not options.oformat:
@@ -2752,10 +2773,10 @@ def map_to_js_libs(library_name):
 
 
 def process_libraries(options, flags):
+  """Process `-l` and `--js-library` flags."""
   new_flags = []
   system_libs_map = system_libs.Library.get_usable_variations()
 
-  # Process `-l` and `--js-library` flags
   for flag in flags:
     if flag.startswith('--js-library='):
       js_lib = flag.split('=', 1)[1]
@@ -2793,22 +2814,22 @@ def process_libraries(options, flags):
       continue
 
     static_lib = f'lib{lib}.a'
-    if not settings.RELOCATABLE and not find_library(static_lib, options.lib_dirs):
+    if not find_library(static_lib, options.lib_dirs):
       # Normally we can rely on the native linker to expand `-l` args.
       # However, emscripten also supports `.so` files that are actually just
       # regular object file.  This means we need to support `.so` files even
       # when statically linking.  The native linker (wasm-ld) will otherwise
       # ignore .so files in this mode.
-      found_dylib = False
+      found_fake_dylib = False
       for ext in DYLIB_EXTENSIONS:
         name = 'lib' + lib + ext
         path = find_library(name, options.lib_dirs)
-        if path:
-          found_dylib = True
+        if path and not building.is_wasm_dylib(path):
+          found_fake_dylib = True
           new_flags.append(path)
           break
 
-      if found_dylib:
+      if found_fake_dylib:
         continue
 
     new_flags.append(flag)
@@ -2876,7 +2897,7 @@ def replacement(self):
 
 
 def filter_out_fake_dynamic_libs(options, inputs):
-  # Filters out "fake" dynamic libraries that are really just intermediate object files.
+  """Filter out "fake" dynamic libraries that are really just intermediate object files."""
   def is_fake_dylib(input_file):
     if get_file_suffix(input_file) in DYLIB_EXTENSIONS and os.path.exists(input_file) and not building.is_wasm_dylib(input_file):
       if not options.ignore_dynamic_linking:
@@ -2888,11 +2909,13 @@ def is_fake_dylib(input_file):
   return [f for f in inputs if not is_fake_dylib(f)]
 
 
-def filter_out_duplicate_dynamic_libs(inputs):
+def filter_out_duplicate_fake_dynamic_libs(inputs):
+  """Filter out duplicate "fake" shared libraries (intermediate object files).
+
+  See test_core.py:test_redundant_link
+  """
   seen = set()
 
-  # Filter out duplicate "fake" shared libraries (intermediate object files).
-  # See test_core.py:test_redundant_link
   def check(input_file):
     if get_file_suffix(input_file) in DYLIB_EXTENSIONS and not building.is_wasm_dylib(input_file):
       abspath = os.path.abspath(input_file)
@@ -3108,11 +3131,10 @@ def phase_calculate_linker_inputs(options, linker_args):
   if options.oformat == OFormat.OBJECT or options.ignore_dynamic_linking:
     linker_args = filter_out_fake_dynamic_libs(options, linker_args)
   else:
-    linker_args = filter_out_duplicate_dynamic_libs(linker_args)
+    linker_args = filter_out_duplicate_fake_dynamic_libs(linker_args)
 
-  if settings.MAIN_MODULE:
-    dylibs = [a for a in linker_args if building.is_wasm_dylib(a)]
-    process_dynamic_libs(dylibs, options.lib_dirs)
+  if not settings.SIDE_MODULE and not settings.FAKE_DYLIBS:
+    process_dynamic_libs(options.dylibs, options.lib_dirs)
 
   return linker_args