core/assert: check assert at compile time, if possible

boards/lora-e5-dev/board.c

@@ -30,12 +30,12 @@
 
 void board_init(void)
 {
     if(IS_ACTIVE(CONFIG_LORA_E5_DEV_ENABLE_3P3V)) {
         gpio_init(LORA_E5_DEV_3P3V_ENABLE_PIN, GPIO_OUT);
         gpio_set(LORA_E5_DEV_3P3V_ENABLE_PIN);
     }
 
     if(IS_ACTIVE(CONFIG_LORA_E5_DEV_ENABLE_5V)) {
         gpio_init(LORA_E5_DEV_5V_ENABLE_PIN, GPIO_OUT);
         gpio_set(LORA_E5_DEV_5V_ENABLE_PIN);
     }
@@ -68,7 +68,7 @@
         break;
     default:
         /* SX126X_RF_MODE_TX_LPA is not supported */
-        assert(0);
+        assert_unreachable();
         break;
     }
 }

core/lib/assert.c

@@ -24,7 +24,7 @@
 #include "backtrace.h"
 #endif
 
-__NORETURN void _assert_failure(const char *file, unsigned line)
+__NORETURN void _assert_panic_verbose(const char *file, unsigned line)
 {
     printf("%s:%u => ", file, line);
 #if IS_USED(MODULE_BACKTRACE)
@@ -37,7 +37,7 @@ __NORETURN void _assert_failure(const char *file, unsigned line)
     core_panic(PANIC_ASSERT_FAIL, "FAILED ASSERTION.");
 }
 
-__NORETURN void _assert_panic(void)
+__NORETURN void _assert_panic_concise(void)
 {
     printf("%" PRIxTXTPTR "\n", cpu_get_caller_pc());
 #if IS_USED(MODULE_BACKTRACE)

core/lib/include/assert.h

@@ -58,44 +58,23 @@
  * in an endless while loop.
  */
 #define DEBUG_ASSERT_BREAKPOINT
-#else
-/* we should not include custom headers in standard headers */
-#define _likely(x)      __builtin_expect((uintptr_t)(x), 1)
-#endif
 
 /**
- * @def __NORETURN
- * @brief hidden (__) NORETURN definition
- * @internal
+ * @brief   abort the program if assertion is false
  *
- * Duplicating the definitions of kernel_defines.h as these are unsuitable for
- * system header files like the assert.h.
- * kernel_defines.h would define symbols that are not reserved.
- */
-#ifndef __NORETURN
-#ifdef __GNUC__
-#define __NORETURN __attribute__((noreturn))
-#else /*__GNUC__*/
-#define __NORETURN
-#endif /*__GNUC__*/
-#endif /*__NORETURN*/
-
-#ifdef NDEBUG
-#define assert(ignore)((void)0)
-#elif defined(DEBUG_ASSERT_VERBOSE)
-/**
- * @brief   Function to handle failed assertion
+ * @warning Do not use `assert(0);` to assert that a line of code is
+ *          unreachable, @ref assert_unreachable instead.
  *
- * @note    This function was introduced for memory size optimization
+ * @note    This implementation has a special twist: It will fail at link time
+ *          if the condition can be proven to be never true at compile time.
+ *          If linking fails due to the symbol
+ *          `__assertion_is_known_to_fail_at_compile_time` being undefined,
+ *          an assertion has been proven to always blow by the optimizer.
  *
- * @warning this function **NEVER** returns!
- *
- * @param[in] file  The file name of the file the assertion failed in
- * @param[in] line  The code line of @p file the assertion failed in
- */
-__NORETURN void _assert_failure(const char *file, unsigned line);
-/**
- * @brief    abort the program if assertion is false
+ * @note    Further note that when packages include this header, the check
+ *          will always be performed at runtime, as replacing all
+ *          `assert(0);` in packages with `assert_unreachable();` are not
+ *          maintainable.
  *
  * If the macro NDEBUG was defined at the moment <assert.h> was last included,
  * the macro assert() generates no code, and hence does nothing at all.
@@ -134,27 +113,109 @@
  *
  * @see http://pubs.opengroup.org/onlinepubs/9699919799/functions/assert.html
  */
-#define assert(cond) (_likely(cond) ? (void)0 :  _assert_failure(__FILE__, __LINE__))
-#else /* DEBUG_ASSERT_VERBOSE */
-__NORETURN void _assert_panic(void);
-#define assert(cond) (_likely(cond) ? (void)0 : _assert_panic())
-#endif /* DEBUG_ASSERT_VERBOSE */
+#  define assert(cond) /* implementation */
+
+/**
+ * @brief   abort the program if this line is reached, unless `NDEBUG` is
+ *          defined
+ */
+#  define assert_unreachable() /* implementation */
+#else
+/* we should not include custom headers in standard headers */
+#  define _likely(x)    __builtin_expect((uintptr_t)(x), 1)
+#endif
+
+/**
+ * @def __NORETURN
+ * @brief hidden (__) NORETURN definition
+ * @internal
+ *
+ * Duplicating the definitions of kernel_defines.h as these are unsuitable for
+ * system header files like the assert.h.
+ * kernel_defines.h would define symbols that are not reserved.
+ */
+#ifndef __NORETURN
+#  ifdef __GNUC__
+#    define __NORETURN __attribute__((noreturn))
+#  else /*__GNUC__*/
+#    define __NORETURN
+#  endif /*__GNUC__*/
+#endif /*__NORETURN*/
+
+/**
+ * @brief   Function to report a failed assertion - verbose variant
+ *
+ * @warning This function is internal and should not be used by downstream code.
+ *
+ * @note    This function was introduced for memory size optimization
+ *
+ * @warning this function **NEVER** returns!
+ *
+ * @param[in] file  The file name of the file the assertion failed in
+ * @param[in] line  The code line of @p file the assertion failed in
+ */
+__NORETURN void _assert_panic_verbose(const char *file, unsigned line);
+
+/**
+ * @brief   Concise version of reporting a blown assertion
+ *
+ * @warning This function is internal and should not be used by downstream code.
+ *
+ * This is an alternative to @ref _assert_panic_verbose that doesn't require
+ * the caller to spent memory in `.rodata` for a file name and a line number.
+ */
+__NORETURN void _assert_panic_concise(void);
+
+#ifdef NDEBUG
+#  define assert(ignore)                ((void)0)
+#  define assert_unreachable()          UNREACHABLE()
+#else
+#  if DEBUG_ASSERT_VERBOSE
+#    define _assert_panic(file, line) _assert_panic_verbose(file, line)
+#  else
+#    define _assert_panic(file, line) _assert_panic_concise()
+#  endif
+#  if COMPILING_RIOT_PKG_CODE
+#    define assert(cond) \
+        (_likely(cond) ? (void)0 : _assert_panic(__FILE__, __LINE__))
+#  else
+#    define assert(cond) \
+        do { \
+            if (__builtin_constant_p(cond)) { \
+                if (!(cond)) { \
+                    extern void __assertion_is_known_to_fail_at_compile_time(void); \
+                    __assertion_is_known_to_fail_at_compile_time(); \
+                } \
+            } \
+            else { \
+                if (!(_likely(cond))) { \
+                    _assert_panic(__FILE__, __LINE__); \
+                } \
+            } \
+        } \
+        while (0)
+#  endif
+#  define assert_unreachable() \
+        do { \
+            _assert_panic(__FILE__, __LINE__); \
+        } while (0)
+#endif
 
 #if !defined __cplusplus
-#if __STDC_VERSION__ >= 201112L
+#  if __STDC_VERSION__ >= 201112L
 /**
  * @brief c11 static_assert() macro
  */
-#define static_assert(...) _Static_assert(__VA_ARGS__)
-#else
+#    define static_assert(...) _Static_assert(__VA_ARGS__)
+#  else
 /**
  * @brief static_assert for c-version < c11
  *
  * Generates a division by zero compile error when cond is false
  */
-#define static_assert(cond, ...) \
-    { enum { static_assert_failed_on_div_by_0 = 1 / (!!(cond)) }; }
-#endif
+#    define static_assert(cond, ...) \
+        { enum { static_assert_failed_on_div_by_0 = 1 / (!!(cond)) }; }
+#  endif
 #endif
 
 #ifdef __cplusplus

cpu/atmega_common/periph/rtt.c

@@ -204,7 +204,7 @@ static inline uint8_t _rtt_div(uint16_t freq)
         case 256:   return 0x5;
         case 128:   return 0x6;
         case 32:    return 0x7;
-        default:    assert(0);
+        default:    assert_unreachable();
                     return 0;
     }
 }

cpu/cc2538/radio/cc2538_rf_radio_ops.c

@@ -154,7 +154,7 @@
             RFCORE_XREG_CSPY = cc2538_min_be; /* Holds MinBE */
 
             assert(cc2538_csma_ca_retries >= 0);
             RFCORE_XREG_CSPZ = cc2538_csma_ca_retries + 1; /* Holds CSMA-CA attempts (retries + 1) */
 
             RFCORE_XREG_CSPCTRL &= ~CC2538_CSP_MCU_CTRL_MASK;
 
@@ -287,7 +287,7 @@
     /* The upper layer shouldn't call this function if the RX_DONE event was
      * not triggered */
     if (!(RFCORE_XREG_RXFIFOCNT > 0)) {
-        assert(false);
+        assert_unreachable();
     }
 
     pkt_len = rfcore_read_byte() - IEEE802154_FCS_LEN;
@@ -391,7 +391,7 @@
 
     if ((flags_f0 & SFD)) {
         handled_f0 |= SFD;
         switch(cc2538_state) {
         case CC2538_STATE_READY:
             cc2538_rf_hal->cb(cc2538_rf_hal, IEEE802154_RADIO_INDICATION_RX_START);
             break;
@@ -406,7 +406,7 @@
         default:
             /* This should never happen */
             DEBUG("ERROR: cc2538_state: %i\n", cc2538_state);
-            assert(false);
+            assert_unreachable();
         }
     }
 
@@ -464,7 +464,7 @@
         default:
             /* This should never happen */
             DEBUG("ERROR: cc2538_state: %i\n", cc2538_state);
-            assert(false);
+            assert_unreachable();
             break;
         }
     }
@@ -485,7 +485,7 @@
     const network_uint16_t *short_addr = value;
     const eui64_t *ext_addr = value;
     const uint16_t *pan_id = value;
     switch(cmd) {
         case IEEE802154_AF_SHORT_ADDR:
             RFCORE_FFSM_SHORT_ADDR0 = short_addr->u8[1];
             RFCORE_FFSM_SHORT_ADDR1 = short_addr->u8[0];
@@ -511,10 +511,10 @@
     return 0;
 }
 
 static int _config_src_addr_match(ieee802154_dev_t *dev, ieee802154_src_match_t cmd, const void *value)
 {
     (void) dev;
     switch(cmd) {
         case IEEE802154_SRC_MATCH_EN:
             RFCORE_XREG_FRMCTRL1 &= ~CC2538_FRMCTRL1_PENDING_OR_MASK;
             if (*((const bool*) value) == true) {

cpu/esp32/esp-ble-nimble/esp_ble_nimble.c

@@ -185,7 +185,7 @@ static int _esp_hci_h4_frame_cb(uint8_t pkt_type, void *data)
         rc = ble_transport_to_hs_evt(data);
         break;
     default:
-        assert(0);
+        assert_unreachable();
         break;
     }
 
@@ -202,24 +202,24 @@ void esp_ble_nimble_init(void)
         LOG_TAG_ERROR(LOG_TAG,
                       "Bluetooth controller release classic bt memory failed: %s",
                       esp_err_to_name(ret));
-        assert(0);
+        assert_unreachable();
     }
     */
 
     /* init and enable the Bluetooth LE controller */
     if ((ret = esp_bt_controller_init(&bt_cfg)) != ESP_OK) {
         LOG_TAG_ERROR(LOG_TAG, "Bluetooth controller initialize failed: %d", ret);
-        assert(0);
+        assert_unreachable();
     }
 
     if ((ret = esp_bt_controller_enable(ESP_BT_MODE_BLE)) != ESP_OK) {
         LOG_TAG_ERROR(LOG_TAG, "Bluetooth controller enable failed: %d", ret);
-        assert(0);
+        assert_unreachable();
     }
 
     /* register callbacks from Bluetooth LE controller */
     if ((ret = esp_vhci_host_register_callback(&vhci_host_cb)) != ESP_OK) {
-        assert(0);
+        assert_unreachable();
     }
 
     /* init HCI H4 processing */

cpu/esp32/periph/can.c

@@ -597,7 +597,7 @@ static void _esp_can_power_up(can_t *dev)
      * pending interrupts cleared */
 
     if (!twai_hal_init(&hw)) {
-        assert(false);
+        assert_unreachable();
     }
 
     /* set bittiming from parameters as given in device data */

cpu/esp32/periph/i2c_hw.c

@@ -132,7 +132,7 @@ void i2c_init(i2c_t dev)
                        i2c_config[dev].scl, i2c_config[dev].sda,
                        gpio_get_pin_usage_str(i2c_config[dev].scl),
                        gpio_get_pin_usage_str(i2c_config[dev].sda));
-        assert(0);
+        assert_unreachable();
     }
 
     _i2c_bus[dev].cmd = 0;
@@ -169,7 +169,7 @@ void i2c_init(i2c_t dev)
             break;
         default:
             LOG_TAG_ERROR("i2c", "Invalid speed value in %s\n", __func__);
-            assert(0);
+            assert_unreachable();
     }
 
     _i2c_bus[dev].clk_freq = cfg.master.clk_speed;

cpu/esp32/periph/sdmmc.c

@@ -201,11 +201,11 @@ static void _init(sdmmc_dev_t *sdmmc_dev)
 
     if ((res = sdmmc_host_init())) {
         LOG_ERROR("[sdmmc] Could not initialize SDMMC host controller\n");
-        assert(false);
+        assert_unreachable();
     }
     if ((res = sdmmc_host_init_slot(dev->config->slot, &slot_config))) {
         LOG_ERROR("[sdmmc] Could not initialize SDMMC slot\n");
-        assert(false);
+        assert_unreachable();
     }
 
     if (gpio_is_valid(conf->cd)) {

cpu/esp32/periph/spi.c

@@ -277,7 +277,7 @@
         LOG_TAG_ERROR("spi",
                       "SPI_DEV(%d) CS signal could not be initialized\n",
                       bus);
-        assert(0);
+        assert_unreachable();
     }
 
     /* lock the bus */
@@ -286,7 +286,7 @@
     /*
      * set SPI mode
      * see ESP32 Technical Reference, Section 7.4.1, Table 27
      * https://www.espressif.com/sites/default/files/documentation/esp32_technical_reference_manual_en.pdf
      */
 
     /* hardware CS not used (TODO) */
@@ -302,7 +302,7 @@
     /*
      * set SPI clock
      * see ESP32 Technical Reference, Section 7.8 SPI_CLOCK_REG
      * https://www.espressif.com/sites/default/files/documentation/esp32_technical_reference_manual_en.pdf
      */
 
     /* check whether timing has to be recalculated (time consuming) */
@@ -314,7 +314,7 @@
             LOG_TAG_ERROR("spi", "APB clock rate (%"PRIu32" Hz) has to be at "
                           "least 5 times SPI clock rate (%d Hz)\n",
                           apb_clk, clk);
-            assert(false);
+            assert_unreachable();
         }
 
         /* duty cycle is measured in is 1/256th, 50% = 128 */

cpu/esp8266/periph/spi.c

@@ -240,7 +240,7 @@
         LOG_TAG_ERROR("spi",
                       "SPI_DEV(%d) CS signal could not be initialized\n",
                       bus);
-        assert(0);
+        assert_unreachable();
     }
 
     /* lock the bus */
@@ -259,7 +259,7 @@
 
     /* set SPI clock
      * see ESP8266 Technical Reference Appendix 2 - SPI registers
      * https://www.espressif.com/sites/default/files/documentation/esp8266-technical_reference_en.pdf
      */
 
     uint32_t spi_clkdiv_pre;    /* 13 bit */

cpu/esp8266/vendor/esp-idf/esp8266/source/startup.c

@@ -60,26 +60,26 @@ static void user_init_entry(void *param)
 #endif
 
     if (nvs_flash_init() != 0) {
-        assert(0);
+        assert_unreachable();
     }
     if (wifi_nvs_init() != 0) {
-        assert(0);
+        assert_unreachable();
     }
     if (esp_rtc_init() != 0) {
-        assert(0);
+        assert_unreachable();
     }
     if (mac_init() != 0) {
-        assert(0);
+        assert_unreachable();
     }
     if (base_gpio_init() != 0) {
-        assert(0);
+        assert_unreachable();
     };
 
     esp_phy_load_cal_and_init(0);
 
 #ifdef MODULE_ESP_WIFI_ANY
     if (wifi_timer_init() != 0) {
-        assert(0);
+        assert_unreachable();
     }
 #endif
 
@@ -95,7 +95,7 @@ static void user_init_entry(void *param)
 
 #ifdef CONFIG_ENABLE_PTHREAD
     if (esp_pthread_init() != 0) {
-        assert(0);
+        assert_unreachable();
     }
 #endif
 
@@ -163,7 +163,7 @@ void call_user_start(size_t start_addr)
     wifi_os_init();
 
     if (wifi_task_create(user_init_entry, "uiT", CONFIG_MAIN_TASK_STACK_SIZE, NULL, wifi_task_get_max_priority()) == NULL) {
-        assert(0);
+        assert_unreachable();
     }
 
     wifi_os_start();