[esp32] Eliminate dead exception class code via linker wraps

esphome/components/esp32/__init__.py

@@ -1048,6 +1048,17 @@ async def to_code(config):
         cg.add_build_flag("-DUSE_ESP32_FRAMEWORK_ESP_IDF")
         if use_platformio:
             cg.add_platformio_option("framework", "espidf")
+
+        # Wrap std::__throw_* functions to abort immediately, eliminating ~1KB of
+        # exception class overhead. See throw_stubs.cpp for implementation.
+        # ESP-IDF wraps __cxa_throw but not these higher-level functions.
+        # Mangled names: _ZSt = std::, number = identifier length, PKc = char const*
+        cg.add_build_flag("-Wl,--wrap=_ZSt20__throw_length_errorPKc")
+        cg.add_build_flag("-Wl,--wrap=_ZSt19__throw_logic_errorPKc")
+        cg.add_build_flag("-Wl,--wrap=_ZSt20__throw_out_of_rangePKc")
+        cg.add_build_flag("-Wl,--wrap=_ZSt24__throw_out_of_range_fmtPKcz")
+        cg.add_build_flag("-Wl,--wrap=_ZSt17__throw_bad_allocv")
+        cg.add_build_flag("-Wl,--wrap=_ZSt25__throw_bad_function_callv")
     else:
         cg.add_build_flag("-DUSE_ARDUINO")
         cg.add_build_flag("-DUSE_ESP32_FRAMEWORK_ARDUINO")

esphome/components/esp32/throw_stubs.cpp

@@ -0,0 +1,53 @@
+/*
+ * Linker wrap stubs for std::__throw_* functions.
+ *
+ * ESP-IDF disables C++ exceptions but doesn't wrap the std::__throw_*
+ * functions that construct exception objects before calling __cxa_throw.
+ * This wastes ~1KB on exception class code that can never execute.
+ *
+ * These stubs abort immediately with a descriptive message, allowing
+ * the linker to dead-code eliminate the exception class infrastructure.
+ *
+ * The ESP8266 Arduino toolchain solves this by rebuilding libstdc++ with
+ * similar stubs. We achieve the same result using linker --wrap.
+ *
+ * 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()
+ */
+
+#ifdef USE_ESP_IDF
+#include "esp_system.h"
+
+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*, ...)
+// Called by bitset::to_ulong when value doesn't fit
+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"
+#endif  // USE_ESP_IDF