Wrap dead exceptions code to save some flash (#149)

Author: Jason2866

CMakeLists.txt

@@ -35,3 +35,22 @@ add_custom_command(
 add_custom_target(mem-variant DEPENDS "mem_variant")
 
 idf_build_set_property(COMPILE_DEFINITIONS "-DESP32_ARDUINO_LIB_BUILDER" APPEND)
+
+# Wrap std::__throw_* functions to abort immediately, eliminating ~2KB of
+# exception class overhead. Implementation lives in components/throw_stubs.
+# ESP-IDF already compiles with -fno-exceptions, so this code was dead anyway.
+# Apply directly on the project elf so the flags end up in
+# build/CMakeFiles/${CMAKE_PROJECT_NAME}.elf.dir/link.txt and get picked up by
+# tools/copy-libs.sh into pioarduino-build.py LINKFLAGS / flags/ld_flags.
+
+target_link_options(${CMAKE_PROJECT_NAME}.elf PRIVATE
+    "-Wl,--wrap=_ZSt20__throw_length_errorPKc"
+    "-Wl,--wrap=_ZSt19__throw_logic_errorPKc"
+    "-Wl,--wrap=_ZSt20__throw_out_of_rangePKc"
+    "-Wl,--wrap=_ZSt24__throw_out_of_range_fmtPKcz"
+    "-Wl,--wrap=_ZSt17__throw_bad_allocv"
+    "-Wl,--wrap=_ZSt25__throw_bad_function_callv"
+    # Keep at least one __wrap_* symbol referenced so the object is pulled
+    # from libthrow_stubs.a during the user sketch link.
+    "-u__wrap__ZSt17__throw_bad_allocv"
+)

components/throw_stubs/CMakeLists.txt

@@ -0,0 +1,3 @@
+idf_component_register(SRCS "throw_stubs.cpp"
+                       INCLUDE_DIRS ""
+                       REQUIRES esp_system)

components/throw_stubs/throw_stubs.cpp

@@ -0,0 +1,50 @@
+/*
+ * Linker wrap stubs for std::__throw_* functions.
+ *
+ * ESP-IDF compiles with -fno-exceptions, so C++ exceptions always abort.
+ * However, ESP-IDF only wraps low-level functions (__cxa_throw, etc.),
+ * not the std::__throw_* functions that construct exception objects first.
+ * This pulls in ~2KB of dead exception class code that can never run.
+ *
+ * These stubs abort immediately with a descriptive message, allowing
+ * the linker to dead-code eliminate the exception class infrastructure.
+ *
+ * Wrapped functions and their callers:
+ * - std::__throw_length_error: std::string::reserve, std::vector::reserve
+ * - std::__throw_logic_error: std::promise, std::packaged_task
+ * - std::__throw_out_of_range: std::string::at, std::vector::at
+ * - std::__throw_out_of_range_fmt: std::bitset::to_ulong
+ * - std::__throw_bad_alloc: operator new
+ * - std::__throw_bad_function_call: std::function::operator()
+ *
+ * Source: https://github.com/esphome/esphome/blob/dev/esphome/components/esp32/throw_stubs.cpp
+ */
+
+#include "esp_system.h"
+
+// Linker wraps for std::__throw_* - must be extern "C" at global scope.
+// Names must be __wrap_ + mangled name for the linker's --wrap option.
+
+// NOLINTBEGIN(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp,readability-identifier-naming)
+extern "C" {
+
+// std::__throw_length_error(char const*) - called when container size exceeds max_size()
+void __wrap__ZSt20__throw_length_errorPKc(const char *) { esp_system_abort("std::length_error"); }
+
+// std::__throw_logic_error(char const*) - called for logic errors (e.g., promise already satisfied)
+void __wrap__ZSt19__throw_logic_errorPKc(const char *) { esp_system_abort("std::logic_error"); }
+
+// std::__throw_out_of_range(char const*) - called by at() when index is out of bounds
+void __wrap__ZSt20__throw_out_of_rangePKc(const char *) { esp_system_abort("std::out_of_range"); }
+
+// std::__throw_out_of_range_fmt(char const*, ...) - variadic form called by container at() with formatted messages
+void __wrap__ZSt24__throw_out_of_range_fmtPKcz(const char *, ...) { esp_system_abort("std::out_of_range"); }
+
+// std::__throw_bad_alloc() - called when operator new fails
+void __wrap__ZSt17__throw_bad_allocv() { esp_system_abort("std::bad_alloc"); }
+
+// std::__throw_bad_function_call() - called when invoking empty std::function
+void __wrap__ZSt25__throw_bad_function_callv() { esp_system_abort("std::bad_function_call"); }
+
+}  // extern "C"
+// NOLINTEND(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp,readability-identifier-naming)