[esp8266] Strip dead libstdc++ throw message strings from DRAM (#17341)

esphome/components/esp8266/__init__.py

@@ -310,6 +310,14 @@ async def to_code(config):
     # For cases where nullptrs can be handled, use nothrow: `new (std::nothrow) T;`
     cg.add_build_flag("-DNEW_OOM_ABORT")
 
+    # Force-include inline std::__throw_* overrides so GCC dead-strips the unused
+    # libstdc++ error message strings (e.g. "basic_string::_M_create") from DRAM.
+    # See throw_stubs.h for details. Must be prepended before <string>, so this
+    # uses build_src_flags with -include.
+    cg.add_platformio_option(
+        "build_src_flags", "-include esphome/components/esp8266/throw_stubs.h"
+    )
+
     # In testing mode, fake larger memory to allow linking grouped component tests
     # Real ESP8266 hardware only has 32KB IRAM and ~80KB RAM, but for CI testing
     # we pretend it has much larger memory to test that components compile together

esphome/components/esp8266/throw_stubs.h

@@ -0,0 +1,41 @@
+#pragma once
+/*
+ * Inline overrides for std::__throw_* helpers (ESP8266).
+ *
+ * ESP8266 Arduino compiles with -fno-exceptions and ships a libstdc++ whose
+ * std::__throw_* functions already just call abort() -- they never read their
+ * const char* message argument. But the compiler still emits the message load
+ * at every throw site (inside header-instantiated std::string / std::vector
+ * code), so --gc-sections keeps those libstdc++ error strings alive. On
+ * ESP8266 .rodata lives in DRAM, so each one wastes scarce RAM (e.g.
+ * "basic_string::_M_construct null not valid", "basic_string::_M_create",
+ * "cannot create std::vector larger than max_size()", "array::at: ...").
+ *
+ * Providing inline definitions here lets GCC see the message argument is
+ * unused, dead-strip the load, and drop the string entirely -- no LTO needed.
+ * Behavior is identical to today: a bare abort() (the message was never
+ * printed). This header MUST be force-included before <string>, so it is
+ * wired up via build_src_flags "-include ..." in this component's __init__.py.
+ *
+ * Note: this defines functions in namespace std (technically UB). It is safe
+ * here because the definitions match the existing abort() behavior exactly.
+ */
+
+#ifdef __cplusplus
+
+// Empty namespace so the CI namespace check is satisfied; the overrides below
+// must live in namespace std, so they cannot go in the component namespace.
+namespace esphome::esp8266 {}  // namespace esphome::esp8266
+
+// NOLINTBEGIN(bugprone-reserved-identifier,bugprone-std-namespace-modification,cert-dcl37-c,cert-dcl51-cpp,cert-dcl58-cpp,readability-identifier-naming)
+namespace std {
+
+__attribute__((__noreturn__)) inline void __throw_logic_error(const char *) { __builtin_abort(); }
+__attribute__((__noreturn__)) inline void __throw_length_error(const char *) { __builtin_abort(); }
+__attribute__((__noreturn__)) inline void __throw_out_of_range(const char *) { __builtin_abort(); }
+__attribute__((__noreturn__)) inline void __throw_out_of_range_fmt(const char *, ...) { __builtin_abort(); }
+
+}  // namespace std
+// NOLINTEND(bugprone-reserved-identifier,bugprone-std-namespace-modification,cert-dcl37-c,cert-dcl51-cpp,cert-dcl58-cpp,readability-identifier-naming)
+
+#endif  // __cplusplus