Bluetooth: Controller: Reduce assertion check code size

Reduce Controller assertion check code size for ARM Cortex-M
CPUs by using the undefined instruction exception.

`arm-none-eabi-addr2line` commandline can be used to get the
source file and line number.

Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: cvinayak

doc/connectivity/bluetooth/api/hci.txt

@@ -1085,14 +1085,13 @@ represents.
 | Event                         | Event Code | Event Parameters              |
 +-------------------------------+------------+-------------------------------+
 | Fatal_Error                   | 0xFF       | Subevent_Code,                |
-|                               |            | Error_Data_Type,              |
 |                               |            | Error_Data                    |
 +-------------------------------+------------+-------------------------------+
 
-The Error_Data_Type provides an information about what is the Error_Data size
-and content.
+The Subevent_Code provides an information about what is the Error_Data size and
+content.
 
-	Error_Data_Type:                                Size: 1 Octet
+	Subevent_Code:                                  Size: 1 Octet
 	+--------------------+--------------------------------------+
 	| Value              | Parameter Description                |
 	+--------------------+--------------------------------------+
@@ -1157,6 +1156,7 @@ Zephyr Fatal Error event may be generated by k_sys_fatal_error_handler.
 	| a4                 | 4 octets | General purpose register        |
 	| ip                 | 4 octets | Instruction pointer register    |
 	| lr                 | 4 octets | Link register                   |
+	| pc                 | 4 octets | Program counter register        |
 	| xpsr               | 4 octets | Program status register         |
 	+--------------------+--------------------------------------------+
 

include/zephyr/bluetooth/hci_vs.h

@@ -222,8 +222,6 @@ struct bt_hci_evt_vs {
 	uint8_t  subevent;
 } __packed;
 
-#define BT_HCI_EVT_VS_FATAL_ERROR              0x02
-
 #define BT_HCI_EVT_VS_ERROR_DATA_TYPE_STACK_FRAME   0x01
 #define BT_HCI_EVT_VS_ERROR_DATA_TYPE_CTRL_ASSERT   0x02
 #define BT_HCI_EVT_VS_ERROR_DATA_TYPE_TRACE         0x03
@@ -234,8 +232,10 @@ struct bt_hci_vs_fata_error_cpu_data_cortex_m {
 	uint32_t a4;
 	uint32_t ip;
 	uint32_t lr;
+	uint32_t pc;
 	uint32_t xpsr;
 } __packed;
+
 #define BT_HCI_EVT_VS_ERROR_CPU_TYPE_CORTEX_M  0x01
 struct bt_hci_vs_fatal_error_stack_frame {
 	uint32_t reason;

subsys/bluetooth/controller/Kconfig

@@ -1188,6 +1188,9 @@ rsource "Kconfig.df"
 rsource "Kconfig.ll_sw_split"
 rsource "Kconfig.dtm"
 
+config BT_CTLR_ASSERT_OPTIMIZE_FOR_SIZE_SUPPORT
+	bool
+
 config BT_CTLR_ASSERT_DEBUG
 	bool "Development asserts"
 	default y
@@ -1209,6 +1212,18 @@ config BT_CTLR_ASSERT_HANDLER
 	  and will be invoked whenever the controller code encounters
 	  an unrecoverable error.
 
+config BT_CTLR_ASSERT_OPTIMIZE_FOR_SIZE
+	bool "Assertions optimized for code size"
+	depends on BT_CTLR_ASSERT_OPTIMIZE_FOR_SIZE_SUPPORT
+	default y
+	help
+	  Optimize Controller assertion check for code size.
+
+	  Example, reduces assertion check code size for ARM Cortex-M CPUs by using the undefined
+	  instruction exception.
+	  `arm-none-eabi-addr2line` commandline can be used to get the source file and line number
+	  from the program counter value.
+
 config BT_CTLR_VS_SCAN_REQ_RX
 	bool "Use scan request reporting"
 	depends on BT_HCI_VS && !BT_CTLR_ADV_EXT

subsys/bluetooth/controller/Kconfig.ll_sw_split

@@ -70,6 +70,8 @@ config BT_LLL_VENDOR_NORDIC
 
 	select BT_TICKER_PREFER_START_BEFORE_STOP if BT_TICKER_SLOT_AGNOSTIC
 
+	select BT_CTLR_ASSERT_OPTIMIZE_FOR_SIZE_SUPPORT if CPU_CORTEX_M
+
 	default y
 	help
 	  Use Nordic Lower Link Layer implementation.

subsys/bluetooth/controller/hal/debug.h

@@ -1,31 +1,66 @@
 /*
- * Copyright (c) 2016 Nordic Semiconductor ASA
+ * Copyright (c) 2016-2025 Nordic Semiconductor ASA
  * Copyright (c) 2016 Vinayak Kariappa Chettimada
  *
  * SPDX-License-Identifier: Apache-2.0
  */
 
 #include "common/assert.h"
 
-#ifdef CONFIG_BT_CTLR_ASSERT_HANDLER
+#if defined(CONFIG_BT_CTLR_ASSERT_HANDLER)
 void bt_ctlr_assert_handle(char *file, uint32_t line);
+
+#if defined(CONFIG_BT_CTLR_ASSERT_OPTIMIZE_FOR_SIZE)
+BUILD_ASSERT(IS_ENABLED(CONFIG_CPU_CORTEX_M));
+/* Generate assertion as undefined instruction exception.
+ */
+#define LL_ASSERT(x) \
+	do { \
+		if (unlikely(!(x))) { \
+			__asm__ inline volatile (".inst 0xde00\n"); \
+		} \
+	} while (0)
+
+#else /* !CONFIG_BT_CTLR_ASSERT_OPTIMIZE_FOR_SIZE */
+/* Generate assertion with file name and line number.
+ * NOTE: Variable code size increase per assertion check, depends on full file name path string
+ *       length.
+ */
 #define LL_ASSERT(cond) \
-		if (!(cond)) { \
+		if (unlikely(!(cond))) { \
 			BT_ASSERT_PRINT(cond); \
 			bt_ctlr_assert_handle(__FILE__, __LINE__); \
 		}
+#endif /* !CONFIG_BT_CTLR_ASSERT_OPTIMIZE_FOR_SIZE */
+
 #define LL_ASSERT_MSG(cond, fmt, ...) \
-		if (!(cond)) { \
+		if (unlikely(!(cond))) { \
 			BT_ASSERT_PRINT(cond); \
 			BT_ASSERT_PRINT_MSG(fmt, ##__VA_ARGS__); \
 			bt_ctlr_assert_handle(__FILE__, __LINE__); \
 		}
-#else
+
+#else /* !CONFIG_BT_CTLR_ASSERT_HANDLER */
+
+#if defined(CONFIG_BT_CTLR_ASSERT_OPTIMIZE_FOR_SIZE)
+BUILD_ASSERT(IS_ENABLED(CONFIG_CPU_CORTEX_M));
+/* Generate assertion as undefined instruction exception.
+ */
+#define LL_ASSERT(x) \
+	do { \
+		if (unlikely(!(x))) { \
+			__asm__ inline volatile (".inst 0xde00\n"); \
+		} \
+	} while (0)
+
+#else /* !CONFIG_BT_CTLR_ASSERT_OPTIMIZE_FOR_SIZE */
 #define LL_ASSERT(cond) \
 		BT_ASSERT(cond)
+#endif /* !CONFIG_BT_CTLR_ASSERT_OPTIMIZE_FOR_SIZE */
+
 #define LL_ASSERT_MSG(cond, fmt, ...) \
 		BT_ASSERT_MSG(cond, fmt, ##__VA_ARGS__)
-#endif
+#endif /* !CONFIG_BT_CTLR_ASSERT_HANDLER */
 
 /* Fatal asserts.
  * The Controller will otherwise misbehave causing memory leak or system-wide memory corruptions due

subsys/bluetooth/controller/hci/hci.c

@@ -5284,6 +5284,7 @@ static void vs_err_fatal_cpu_data_fill(bt_hci_vs_fatal_error_cpu_data *cpu_data,
 	cpu_data->a4 = sys_cpu_to_le32(esf->basic.a4);
 	cpu_data->ip = sys_cpu_to_le32(esf->basic.ip);
 	cpu_data->lr = sys_cpu_to_le32(esf->basic.lr);
+	cpu_data->pc = sys_cpu_to_le32(esf->basic.pc);
 	cpu_data->xpsr = sys_cpu_to_le32(esf->basic.xpsr);
 }
 #endif /* CONFIG_CPU_CORTEX_M */