Ensure that required symbols are available to FFI even when the final binary is linked with -dead_strip

pkgs/ffigen/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 16.0.1-wip
+
+- Ensure that required symbols are available to FFI even when the final binary
+  is linked with `-dead_strip`.
+
 ## 16.0.0
 
 - Ensure all protocols referenced in bindings are available at runtime.

pkgs/ffigen/example/swift/third_party/swift_api.h

@@ -1,4 +1,4 @@
-// Generated by Apple Swift version 5.9 (swiftlang-5.9.0.128.108 clang-1500.0.40.1)
+// Generated by Apple Swift version 6.0.2 effective-5.10 (swiftlang-6.0.2.1.2 clang-1600.0.26.4)
 #ifndef SWIFT_MODULE_SWIFT_H
 #define SWIFT_MODULE_SWIFT_H
 #pragma clang diagnostic push
@@ -40,6 +40,8 @@
 #include <string.h>
 #endif
 #if defined(__cplusplus)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnon-modular-include-in-framework-module"
 #if defined(__arm64e__) && __has_include(<ptrauth.h>)
 # include <ptrauth.h>
 #else
@@ -53,6 +55,7 @@
 # endif
 #pragma clang diagnostic pop
 #endif
+#pragma clang diagnostic pop
 #endif
 
 #if !defined(SWIFT_TYPEDEFS)
@@ -287,6 +290,7 @@ typedef unsigned int swift_uint4  __attribute__((__ext_vector_type__(4)));
 #pragma clang diagnostic ignored "-Wunknown-pragmas"
 #pragma clang diagnostic ignored "-Wnullability"
 #pragma clang diagnostic ignored "-Wdollar-in-identifier-extension"
+#pragma clang diagnostic ignored "-Wunsafe-buffer-usage"
 
 #if __has_attribute(external_source_symbol)
 # pragma push_macro("any")

pkgs/ffigen/lib/src/code_generator/objc_block.dart

@@ -322,6 +322,7 @@ ref.pointer.ref.invoke.cast<$natTrampFnType>().asFunction<$trampFuncFfiDartType>
     s.write('''
 
 typedef $blockTypedef;
+__attribute__((visibility("default"))) __attribute__((used))
 $blockName $fnName($blockName block) NS_RETURNS_RETAINED {
   return ^void($argStr) {
     ${generateRetain('block')};

pkgs/ffigen/pubspec.yaml

@@ -3,7 +3,7 @@
 # BSD-style license that can be found in the LICENSE file.
 
 name: ffigen
-version: 16.0.0
+version: 16.0.1-wip
 description: >
   Generator for FFI bindings, using LibClang to parse C, Objective-C, and Swift
   files.

pkgs/objective_c/CHANGELOG.md

@@ -1,6 +1,8 @@
 ## 4.0.1-wip
 
-- Reduces the changes of duplicate symbols by adding a `DOBJC_` prefix.
+- Reduces the chances of duplicate symbols by adding a `DOBJC_` prefix.
+- Ensure that required symbols are available to FFI even when the final binary
+  is linked with `-dead_strip`.
 
 ## 4.0.0
 

pkgs/objective_c/src/ffi.h

@@ -0,0 +1,12 @@
+// Copyright (c) 2024, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef OBJECTIVE_C_SRC_FFI_H_
+#define OBJECTIVE_C_SRC_FFI_H_
+
+// Ensure that an FFI function, that will appear unused by the linker, will
+// not be removed.
+#define FFI_EXPORT __attribute__((visibility("default"))) __attribute__((used))
+
+#endif // OBJECTIVE_C_SRC_FFI_H_

pkgs/objective_c/src/objective_c.h

@@ -5,28 +5,30 @@
 #ifndef OBJECTIVE_C_SRC_OBJECTIVE_C_H_
 #define OBJECTIVE_C_SRC_OBJECTIVE_C_H_
 
+#include "ffi.h"
 #include "include/dart_api_dl.h"
 #include "objective_c_runtime.h"
 
 // Dispose helper for ObjC blocks that wrap a Dart closure.
-void DOBJC_disposeObjCBlockWithClosure(ObjCBlockImpl* block);
+FFI_EXPORT void DOBJC_disposeObjCBlockWithClosure(ObjCBlockImpl *block);
 
 // Returns whether the block is valid and live. The pointer must point to
 // readable memory, or be null. May (rarely) return false positives.
-bool DOBJC_isValidBlock(ObjCBlockImpl* block);
+FFI_EXPORT bool DOBJC_isValidBlock(ObjCBlockImpl *block);
 
 // Returns a new Dart_FinalizableHandle that will clean up the object when the
 // Dart owner is garbage collected.
-Dart_FinalizableHandle DOBJC_newFinalizableHandle(
-    Dart_Handle owner, ObjCObject *object);
+FFI_EXPORT Dart_FinalizableHandle
+DOBJC_newFinalizableHandle(Dart_Handle owner, ObjCObject *object);
 
 // Delete a finalizable handle. Doesn't run the finalization callback, so
 // doesn't clean up the assocated pointer.
-void DOBJC_deleteFinalizableHandle(Dart_FinalizableHandle handle, Dart_Handle owner);
+FFI_EXPORT void DOBJC_deleteFinalizableHandle(Dart_FinalizableHandle handle,
+                                              Dart_Handle owner);
 
 // Returns a newly allocated bool* (initialized to false) that will be deleted
 // by a Dart_FinalizableHandle when the owner is garbage collected.
-bool* DOBJC_newFinalizableBool(Dart_Handle owner);
+FFI_EXPORT bool *DOBJC_newFinalizableBool(Dart_Handle owner);
 
 // Runs fn(arg) on the main thread. If runOnMainThread is already running on the
 // main thread, fn(arg) is invoked synchronously. Otherwise it is dispatched to
@@ -35,6 +37,6 @@ bool* DOBJC_newFinalizableBool(Dart_Handle owner);
 // This assumes that the main thread is executing its queue. If not, #define
 // NO_MAIN_THREAD_DISPATCH to disable this, and run fn(arg) synchronously. The
 // flutter runner does execute the main dispatch queue, but the Dart VM doesn't.
-void DOBJC_runOnMainThread(void (*fn)(void*), void* arg);
+FFI_EXPORT void DOBJC_runOnMainThread(void (*fn)(void *), void *arg);
 
-#endif  // OBJECTIVE_C_SRC_OBJECTIVE_C_H_
+#endif // OBJECTIVE_C_SRC_OBJECTIVE_C_H_

pkgs/objective_c/src/objective_c.m

@@ -5,7 +5,9 @@
 #import <Foundation/NSThread.h>
 #import <dispatch/dispatch.h>
 
-void DOBJC_runOnMainThread(void (*fn)(void*), void* arg) {
+#include "ffi.h"
+
+FFI_EXPORT void DOBJC_runOnMainThread(void (*fn)(void *), void *arg) {
 #ifdef NO_MAIN_THREAD_DISPATCH
   fn(arg);
 #else

pkgs/objective_c/src/objective_c_bindings_generated.m

@@ -13,6 +13,7 @@
 Protocol* _ObjectiveCBindings_NSStreamDelegate() { return @protocol(NSStreamDelegate); }
 
 typedef void  (^_ListenerTrampoline)(id arg0, id arg1, id arg2);
+__attribute__((visibility("default"))) __attribute__((used))
 _ListenerTrampoline _ObjectiveCBindings_wrapListenerBlock_1j2nt86(_ListenerTrampoline block) NS_RETURNS_RETAINED {
   return ^void(id arg0, id arg1, id arg2) {
     objc_retainBlock(block);
@@ -21,6 +22,7 @@ _ListenerTrampoline _ObjectiveCBindings_wrapListenerBlock_1j2nt86(_ListenerTramp
 }
 
 typedef void  (^_ListenerTrampoline1)(void * arg0);
+__attribute__((visibility("default"))) __attribute__((used))
 _ListenerTrampoline1 _ObjectiveCBindings_wrapListenerBlock_ovsamd(_ListenerTrampoline1 block) NS_RETURNS_RETAINED {
   return ^void(void * arg0) {
     objc_retainBlock(block);
@@ -29,6 +31,7 @@ _ListenerTrampoline1 _ObjectiveCBindings_wrapListenerBlock_ovsamd(_ListenerTramp
 }
 
 typedef void  (^_ListenerTrampoline2)(void * arg0, id arg1);
+__attribute__((visibility("default"))) __attribute__((used))
 _ListenerTrampoline2 _ObjectiveCBindings_wrapListenerBlock_wjovn7(_ListenerTrampoline2 block) NS_RETURNS_RETAINED {
   return ^void(void * arg0, id arg1) {
     objc_retainBlock(block);
@@ -37,6 +40,7 @@ _ListenerTrampoline2 _ObjectiveCBindings_wrapListenerBlock_wjovn7(_ListenerTramp
 }
 
 typedef void  (^_ListenerTrampoline3)(void * arg0, id arg1, NSStreamEvent arg2);
+__attribute__((visibility("default"))) __attribute__((used))
 _ListenerTrampoline3 _ObjectiveCBindings_wrapListenerBlock_18d6mda(_ListenerTrampoline3 block) NS_RETURNS_RETAINED {
   return ^void(void * arg0, id arg1, NSStreamEvent arg2) {
     objc_retainBlock(block);
@@ -45,6 +49,7 @@ _ListenerTrampoline3 _ObjectiveCBindings_wrapListenerBlock_18d6mda(_ListenerTram
 }
 
 typedef void  (^_ListenerTrampoline4)(id arg0, id arg1);
+__attribute__((visibility("default"))) __attribute__((used))
 _ListenerTrampoline4 _ObjectiveCBindings_wrapListenerBlock_wjvic9(_ListenerTrampoline4 block) NS_RETURNS_RETAINED {
   return ^void(id arg0, id arg1) {
     objc_retainBlock(block);

pkgs/objective_c/test/main.c

@@ -0,0 +1,27 @@
+// Copyright (c) 2024, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Verify that the required symbols were not stripped from the binary.
+
+#include <dlfcn.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define ASSERT_SYMBOL(s)                                                       \
+  if (dlsym(RTLD_DEFAULT, s) == 0) {                                           \
+    fprintf(stderr, "Missing symbol: %s\n", s);                                \
+    exit(1);                                                                   \
+  }
+
+int main() {
+  ASSERT_SYMBOL("DOBJC_disposeObjCBlockWithClosure"); // objective_c.c
+  ASSERT_SYMBOL("DOBJC_runOnMainThread");
+
+  ASSERT_SYMBOL("DOBJC_disposeObjCBlockWithClosure"); // objective_c.c
+  ASSERT_SYMBOL("DOBJC_runOnMainThread");             // objective_c.m
+  ASSERT_SYMBOL("OBJC_CLASS_$_DOBJCDartProxy");       // proxy.m
+  // objective_c_bindings_generated.m
+  ASSERT_SYMBOL("_ObjectiveCBindings_wrapListenerBlock_ovsamd");
+  return 0;
+}

pkgs/objective_c/test/setup.dart

@@ -19,6 +19,7 @@ final cFiles = [
   'src/include/dart_api_dl.c',
   'test/util.c',
 ].map(_resolve);
+final cMain = _resolve('test/main.c');
 final objCFiles = [
   'src/input_stream_adapter.m',
   'src/objective_c.m',
@@ -74,6 +75,9 @@ String _buildObject(String input, List<String> flags) {
 void _linkLib(List<String> inputs, String output) =>
     _runClang(['-shared', '-undefined', 'dynamic_lookup', ...inputs], output);
 
+void _linkMain(List<String> inputs, String output) =>
+    _runClang(['-dead_strip', '-fobjc-arc', ...inputs], output);
+
 void main(List<String> arguments) {
   final parser = ArgParser();
   parser.addFlag('main-thread-dispatcher');
@@ -96,4 +100,11 @@ void main(List<String> arguments) {
   lib.lookup('OBJC_CLASS_\$_DOBJCDartProxy'); // proxy.m
   // objective_c_bindings_generated.m
   lib.lookup('_ObjectiveCBindings_wrapListenerBlock_ovsamd');
+
+  // Sanity check that the executable can find FFI symbols.
+  _linkMain([...objFiles, cMain], '$cMain.exe');
+  final result = Process.runSync('$cMain.exe', []);
+  if (result.exitCode != 0) {
+    throw Exception('Missing symbols from executable:\n${result.stderr}');
+  }
 }