diff --git a/esphome/components/esp8266/__init__.py b/esphome/components/esp8266/__init__.py index 927a59fd616..1ef4f5e037e 100644 --- a/esphome/components/esp8266/__init__.py +++ b/esphome/components/esp8266/__init__.py @@ -23,6 +23,7 @@ from esphome.helpers import copy_file_if_changed from .boards import BOARDS, ESP8266_LD_SCRIPTS from .const import ( CONF_EARLY_PIN_INIT, + CONF_ENABLE_FULL_PRINTF, CONF_ENABLE_SERIAL, CONF_ENABLE_SERIAL1, CONF_RESTORE_FROM_FLASH, @@ -179,6 +180,7 @@ CONFIG_SCHEMA = cv.All( ), cv.Optional(CONF_ENABLE_SERIAL): cv.boolean, cv.Optional(CONF_ENABLE_SERIAL1): cv.boolean, + cv.Optional(CONF_ENABLE_FULL_PRINTF, default=False): cv.boolean, } ), set_core_data, @@ -260,6 +262,14 @@ async def to_code(config): if CORE.testing_mode: cg.add_build_flag("-DESPHOME_TESTING_MODE") + # Wrap FILE*-based printf functions to eliminate newlib's _vfiprintf_r + # (~1.6 KB). See printf_stubs.cpp for implementation. + if config.get(CONF_ENABLE_FULL_PRINTF): + cg.add_define("USE_FULL_PRINTF") + else: + for symbol in ("vprintf", "printf", "fprintf"): + cg.add_build_flag(f"-Wl,--wrap={symbol}") + cg.add_platformio_option("board_build.flash_mode", config[CONF_BOARD_FLASH_MODE]) ver: cv.Version = CORE.data[KEY_CORE][KEY_FRAMEWORK_VERSION] diff --git a/esphome/components/esp8266/const.py b/esphome/components/esp8266/const.py index 229ac61f245..57eb54f0f80 100644 --- a/esphome/components/esp8266/const.py +++ b/esphome/components/esp8266/const.py @@ -6,6 +6,7 @@ KEY_BOARD = "board" KEY_PIN_INITIAL_STATES = "pin_initial_states" CONF_RESTORE_FROM_FLASH = "restore_from_flash" CONF_EARLY_PIN_INIT = "early_pin_init" +CONF_ENABLE_FULL_PRINTF = "enable_full_printf" CONF_ENABLE_SERIAL = "enable_serial" CONF_ENABLE_SERIAL1 = "enable_serial1" KEY_FLASH_SIZE = "flash_size" diff --git a/esphome/components/esp8266/printf_stubs.cpp b/esphome/components/esp8266/printf_stubs.cpp new file mode 100644 index 00000000000..e6d4a748664 --- /dev/null +++ b/esphome/components/esp8266/printf_stubs.cpp @@ -0,0 +1,71 @@ +/* + * Linker wrap stubs for FILE*-based printf functions. + * + * The ESP8266 Arduino framework and libraries may reference printf(), + * vprintf(), and fprintf() which pull in newlib's _vfprintf_r (~900 bytes). + * ESPHome never uses these — all logging writes directly to the UART via + * Arduino's Serial, so the libc FILE*-based printf path is dead code. + * + * These stubs redirect through vsnprintf() (which is already in the binary + * for ESPHome's logging) and fwrite(), allowing the linker to dead-code + * eliminate _vfprintf_r. + * + * Saves ~1.6 KB of flash. + */ + +#if defined(USE_ESP8266) && !defined(USE_FULL_PRINTF) +#include +#include +#include + +namespace esphome::esp8266 {} + +static constexpr size_t PRINTF_BUFFER_SIZE = 512; + +// These stubs are essentially dead code at runtime — ESPHome writes directly +// to the UART via Arduino's Serial, and Serial.printf() has its own implementation. +// The buffer overflow check is purely defensive and should never trigger. +static int write_printf_buffer(FILE *stream, char *buf, int len) { + if (len < 0) { + return len; + } + size_t write_len = len; + if (write_len >= PRINTF_BUFFER_SIZE) { + fwrite(buf, 1, PRINTF_BUFFER_SIZE - 1, stream); + abort(); + } + if (fwrite(buf, 1, write_len, stream) < write_len || ferror(stream)) { + return -1; + } + return len; +} + +// NOLINTBEGIN(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp,readability-identifier-naming) +extern "C" { + +int __wrap_vprintf(const char *fmt, va_list ap) { + char buf[PRINTF_BUFFER_SIZE]; + return write_printf_buffer(stdout, buf, vsnprintf(buf, sizeof(buf), fmt, ap)); +} + +int __wrap_printf(const char *fmt, ...) { + va_list ap; + va_start(ap, fmt); + int len = __wrap_vprintf(fmt, ap); + va_end(ap); + return len; +} + +int __wrap_fprintf(FILE *stream, const char *fmt, ...) { + va_list ap; + va_start(ap, fmt); + char buf[PRINTF_BUFFER_SIZE]; + int len = write_printf_buffer(stream, buf, vsnprintf(buf, sizeof(buf), fmt, ap)); + va_end(ap); + return len; +} + +} // extern "C" +// NOLINTEND(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp,readability-identifier-naming) + +#endif // USE_ESP8266 && !USE_FULL_PRINTF diff --git a/tests/components/esp8266/test.esp8266-ard.yaml b/tests/components/esp8266/test.esp8266-ard.yaml index 039a2610160..c77218f7a3c 100644 --- a/tests/components/esp8266/test.esp8266-ard.yaml +++ b/tests/components/esp8266/test.esp8266-ard.yaml @@ -1,3 +1,6 @@ +esp8266: + enable_full_printf: false + logger: level: VERBOSE