Merge branch 'feature/cxx_rtti_preparation_v2' into 'master'

C++: add provisions for optional RTTI support (v2)

See merge request espressif/esp-idf!6341

CMakeLists.txt

@@ -27,6 +27,12 @@ else()
     list(APPEND cxx_compile_options "-fno-exceptions")
 endif()
 
+if(CONFIG_COMPILER_CXX_RTTI)
+    list(APPEND cxx_compile_options "-frtti")
+else()
+    list(APPEND cxx_compile_options "-fno-rtti")
+endif()
+
 if(CONFIG_COMPILER_DISABLE_GCC8_WARNINGS)
     list(APPEND compile_options "-Wno-parentheses"
                                 "-Wno-sizeof-pointer-memaccess"

Kconfig

@@ -237,6 +237,15 @@ mainmenu "Espressif IoT Development Framework Configuration"
                 Size (in bytes) of the emergency memory pool for C++ exceptions. This pool will be used to allocate
                 memory for thrown exceptions when there is not enough memory on the heap.
 
+        config COMPILER_CXX_RTTI
+            # Invisible option, until the toolchain with RTTI support is released.
+            # Use prompt "Enable C++ run-time type info (RTTI)" when updating.
+            bool
+            help
+                Enabling this option compiles all C++ files with RTTI support enabled.
+                This increases binary size (typically by tens of kB) but allows using
+                dynamic_cast conversion and typeid operator.
+
         choice COMPILER_STACK_CHECK_MODE
             prompt "Stack smashing protection mode"
             default COMPILER_STACK_CHECK_MODE_NONE

components/esp32/CMakeLists.txt

@@ -56,6 +56,11 @@ else()
         target_linker_script(${COMPONENT_LIB} INTERFACE "ld/esp32.extram.bss.ld")
     endif()
 
+    if(NOT CONFIG_COMPILER_CXX_RTTI)
+        # This has to be linked before esp32.project.ld
+        target_linker_script(${COMPONENT_LIB} INTERFACE "ld/esp32.discard-rtti.ld")
+    endif()
+
     # Process the template file through the linker script generation mechanism, and use the output for linking the
     # final binary
     target_linker_script(${COMPONENT_LIB} INTERFACE "${CMAKE_CURRENT_LIST_DIR}/ld/esp32.project.ld.in" 

components/esp32/component.mk

@@ -9,6 +9,11 @@ ifdef CONFIG_SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY
 	LINKER_SCRIPTS += esp32.extram.bss.ld
 endif
 
+ifndef CONFIG_COMPILER_CXX_RTTI
+	# This linker script must come before esp32.project.ld
+	LINKER_SCRIPTS += esp32.discard-rtti.ld
+endif
+
 # Linker scripts used to link the final application.
 # Warning: These linker scripts are only used when the normal app is compiled; the bootloader
 # specifies its own scripts.

components/esp32/ld/esp32.discard-rtti.ld

@@ -0,0 +1,11 @@
+/* This is only included if CONFIG_COMPILER_CXX_RTTI is not set, to
+ * move RTTI sections of libstdc++ to an unused non-loadable memory region.
+ */
+
+SECTIONS
+{
+  .rodata.discard-rtti (NOLOAD):
+  {
+    *libstdc++.a:(.rodata._ZTI* .rodata._ZTS*)
+  } > discard_seg
+}

components/esp32/ld/esp32.ld

@@ -98,6 +98,11 @@ MEMORY
   /* external memory ,including data and text */
   extern_ram_seg(RWX)  :             org = 0x3F800000,
                                      len = 0x400000
+
+  /* This is not a memory range which can really be accessed; we use it as a "bitbucket"
+     where non-loadable sections, which aren't used at run time, can be discarded.
+   */
+  discard_seg (R) :                  org = 0x00000000, len = 0x10000000
 }
 
 #if defined(CONFIG_ESP32_USE_FIXED_STATIC_RAM_SIZE)

make/project.mk

@@ -468,7 +468,6 @@ CXXFLAGS ?=
 EXTRA_CXXFLAGS ?=
 CXXFLAGS := $(strip \
 	-std=gnu++11 \
-	-fno-rtti \
 	$(OPTIMIZATION_FLAGS) $(DEBUG_FLAGS) \
 	$(COMMON_FLAGS) \
 	$(COMMON_WARNING_FLAGS) \
@@ -481,6 +480,12 @@ else
 CXXFLAGS += -fno-exceptions
 endif
 
+ifdef CONFIG_COMPILER_CXX_RTTI
+CXXFLAGS += -frtti
+else
+CXXFLAGS += -fno-rtti
+endif
+
 ARFLAGS := cru
 
 export CFLAGS CPPFLAGS CXXFLAGS ARFLAGS

tools/cmake/build.cmake

@@ -114,8 +114,7 @@ function(__build_set_default_build_specifications)
     list(APPEND c_compile_options   "-std=gnu99"
                                     "-Wno-old-style-declaration")
 
-    list(APPEND cxx_compile_options "-std=gnu++11"
+    list(APPEND cxx_compile_options "-std=gnu++11")
-                                    "-fno-rtti")
 
     idf_build_set_property(COMPILE_DEFINITIONS "${compile_definitions}" APPEND)
     idf_build_set_property(COMPILE_OPTIONS "${compile_options}" APPEND)