[Zephyr] Fix build issues with LTO

config/nrfconnect/chip-module/CMakeLists.txt

@@ -200,7 +200,6 @@ matter_generate_args_tmp_file()
 # ==============================================================================
 
 matter_build(chip
-    LIB_SHELL   ${CONFIG_CHIP_LIB_SHELL}
     LIB_TESTS   ${CONFIG_CHIP_BUILD_TESTS}
     DEVICE_INFO_EXAMPLE_PROVIDER ${CONFIG_CHIP_EXAMPLE_DEVICE_INFO_PROVIDER}
     GN_DEPENDENCIES kernel
@@ -225,6 +224,16 @@ if (CONFIG_CHIP_MALLOC_SYS_HEAP_OVERRIDE)
     )
 endif()
 
+if (CONFIG_CHIP_LIB_SHELL)
+    # Force pulling chip::Shell::Engine::RunMainLoop() in the final binary.
+    # Without this workaround, the linker script does not process the shell and
+    # init objects defined in MainLoopZephyr.cpp unless the Matter library or
+    # the Matter shell library is linked using the '--whole-archive' flag.
+    target_link_options(chip INTERFACE
+        -Wl,-u,_ZN4chip5Shell6Engine11RunMainLoopEv
+    )
+endif()
+
 # ==============================================================================
 # Define 'chip-ota-image' target for building CHIP OTA image
 # ==============================================================================

examples/all-clusters-app/nrfconnect/prj_release.conf

@@ -62,3 +62,7 @@ CONFIG_CHIP_FACTORY_DATA_BUILD=y
 
 # Enable the Read Client for binding purposes
 CONFIG_CHIP_ENABLE_READ_CLIENT=y
+
+# Enable LTO to reduce the flash usage
+CONFIG_LTO=y
+CONFIG_ISR_TABLES_LOCAL_DECLARATION=y

src/lib/shell/MainLoopZephyr.cpp

@@ -91,15 +91,15 @@ int ExecCommandInShellThread(const struct shell * shell, size_t argc, char ** ar
     return error == CHIP_NO_ERROR ? 0 : -ENOEXEC;
 }
 
-int RegisterCommands()
+int RegisterMatterCommands()
 {
     Shell::Engine::Root().RegisterDefaultCommands();
     return 0;
 }
 
 } // namespace
 
-SYS_INIT(RegisterCommands, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);
+SYS_INIT(RegisterMatterCommands, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);
 SHELL_CMD_ARG_REGISTER(matter, NULL, "Matter commands", ExecCommandInShellThread, 1, CHIP_SHELL_MAX_TOKENS);
 
 namespace chip {

src/platform/Zephyr/SysHeapMalloc.cpp

@@ -30,9 +30,6 @@ extern "C" {
 #include <cstdint>
 #include <cstring>
 
-// Construct name of the given function wrapped with the `--wrap=symbol` GCC option.
-#define WRAP(f) __wrap_##f
-
 using namespace chip;
 
 namespace {
@@ -67,7 +64,7 @@ LockGuard::~LockGuard()
     }
 }
 
-int initHeap()
+int InitSysHeapMalloc()
 {
     sys_heap_init(&sHeap, sHeapMemory, sizeof(sHeapMemory));
     return 0;
@@ -77,7 +74,7 @@ int initHeap()
 
 // Initialize the heap in the POST_KERNEL phase to make sure that it is ready even before
 // C++ static constructors are called (which happens prior to the APPLICATION initialization phase).
-SYS_INIT(initHeap, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);
+SYS_INIT(InitSysHeapMalloc, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);
 
 namespace chip {
 namespace DeviceLayer {
@@ -99,7 +96,7 @@ void * Calloc(size_t num, size_t size)
         return nullptr;
     }
 
-    void * mem = malloc(totalSize);
+    void * mem = Malloc(totalSize);
 
     if (mem)
     {
@@ -156,27 +153,37 @@ void ResetMaxStats()
 
 extern "C" {
 
-void * WRAP(malloc)(size_t size) __attribute((alias("_ZN4chip11DeviceLayer6Malloc6MallocEj")));
-void * WRAP(calloc)(size_t num, size_t size) __attribute((alias("_ZN4chip11DeviceLayer6Malloc6CallocEjj")));
-void * WRAP(realloc)(void * mem, size_t size) __attribute((alias("_ZN4chip11DeviceLayer6Malloc7ReallocEPvj")));
-void WRAP(free)(void * mem) __attribute((alias("_ZN4chip11DeviceLayer6Malloc4FreeEPv")));
+// Construct the name of a function wrapped with the `--wrap=symbol` GCC option.
+#define WRAP(f) __wrap_##f
+
+// Define a function as an alias of another function.
+#define ALIAS(f) __attribute((alias(f)))
+
+// Mark a function as externally visible so that it is not optimized-away even
+// if LTO or whole-program optimization is enabled.
+#define EXTERNALLY_VISIBLE __attribute((externally_visible))
+
+EXTERNALLY_VISIBLE void * WRAP(malloc)(size_t size) ALIAS("_ZN4chip11DeviceLayer6Malloc6MallocEj");
+EXTERNALLY_VISIBLE void * WRAP(calloc)(size_t num, size_t size) ALIAS("_ZN4chip11DeviceLayer6Malloc6CallocEjj");
+EXTERNALLY_VISIBLE void * WRAP(realloc)(void * mem, size_t size) ALIAS("_ZN4chip11DeviceLayer6Malloc7ReallocEPvj");
+EXTERNALLY_VISIBLE void WRAP(free)(void * mem) ALIAS("_ZN4chip11DeviceLayer6Malloc4FreeEPv");
 
-void * WRAP(_malloc_r)(_reent *, size_t size)
+EXTERNALLY_VISIBLE void * WRAP(_malloc_r)(_reent *, size_t size)
 {
     return WRAP(malloc)(size);
 }
 
-void * WRAP(_calloc_r)(_reent *, size_t num, size_t size)
+EXTERNALLY_VISIBLE void * WRAP(_calloc_r)(_reent *, size_t num, size_t size)
 {
     return WRAP(calloc)(num, size);
 }
 
-void * WRAP(_realloc_r)(_reent *, void * mem, size_t size)
+EXTERNALLY_VISIBLE void * WRAP(_realloc_r)(_reent *, void * mem, size_t size)
 {
     return WRAP(realloc)(mem, size);
 }
 
-void WRAP(_free_r)(_reent *, void * mem)
+EXTERNALLY_VISIBLE void WRAP(_free_r)(_reent *, void * mem)
 {
     WRAP(free)(mem);
 }