debug: coredump: fix CRC calcuation for changing data

Fix CRC calculation in the nRF internal flash core dump
backend in the scenario where the data being dumped keeps
changing. This occurs in one of the Core Dump modes that
dumps also the IRQ stack.

The fix is done by writing all data using an intermedate
buffer and doing the CRC calculation on that buffer instead
of input data.

Signed-off-by: Damian Krolik <[email protected]>

Author: Damian-Nordic

subsys/debug/coredump/Kconfig

@@ -4,7 +4,7 @@
 # SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
 #
 
-config DEBUG_COREDUMP_BACKEND_NRF_FLASH_PARTITION
+menuconfig DEBUG_COREDUMP_BACKEND_NRF_FLASH_PARTITION
 	bool "Core dump backend using nRF internal flash/RRAM partition [EXPERIMENTAL]"
 	depends on DEBUG_COREDUMP_BACKEND_OTHER
 	depends on DT_HAS_NORDIC_NRF51_FLASH_CONTROLLER_ENABLED || \
@@ -23,3 +23,11 @@ config DEBUG_COREDUMP_BACKEND_NRF_FLASH_PARTITION
 	  nrfx library directly. This minimizes the dependencies needed to write
 	  the core dump and bypasses synchronization primitives incorporated
 	  into the Zephyr flash drivers.
+
+if DEBUG_COREDUMP_BACKEND_NRF_FLASH_PARTITION
+
+config DEBUG_COREDUMP_BACKEND_NRF_FLASH_PARTITION_WRITE_BUF_SIZE
+	int "Write buffer size"
+	default 128
+
+endif # DEBUG_COREDUMP_BACKEND_NRF_FLASH_PARTITION

subsys/debug/coredump/coredump_backend_nrf_flash_partition.c

@@ -69,13 +69,15 @@ static const uint8_t MAGIC[4] = {'C', 'D', '0', '1'};
 
 enum {
 	HEADER_SIZE = ROUND_UP(sizeof(struct header), FLASH_WRITE_SIZE),
+	WRITE_BUF_SIZE = ROUND_UP(CONFIG_DEBUG_COREDUMP_BACKEND_NRF_FLASH_PARTITION_WRITE_BUF_SIZE,
+				  FLASH_WRITE_SIZE),
 };
 
-static int write_error;			    /* Error occurred when writing a core dump */
-static uint8_t write_buf[FLASH_WRITE_SIZE]; /* Write buffer to assure aligned flash access */
-static size_t write_buf_pos;		    /* # of dump data bytes buffered in the write buffer */
-static size_t write_pos;		    /* # of dump data bytes already written to flash */
-static uint16_t dump_crc;		    /* CRC16 of already written or buffered bytes */
+static int write_error;			  /* Error occurred when writing a core dump */
+static uint8_t write_buf[WRITE_BUF_SIZE]; /* Write buffer to assure aligned flash access */
+static size_t write_buf_pos;		  /* # of dump data bytes buffered in the write buffer */
+static size_t write_pos;		  /* # of dump data bytes already written to flash */
+static uint16_t dump_crc;		  /* CRC16 of already written or buffered bytes */
 
 static inline const struct header *get_stored_header(void)
 {
@@ -229,8 +231,8 @@ static void coredump_nrf_flash_backend_end(void)
 
 	if (write_buf_pos > 0) {
 		/* Flush the write buffer */
-		memset(&write_buf[write_buf_pos], 0, FLASH_WRITE_SIZE - write_buf_pos);
-		write(HEADER_SIZE + write_pos, write_buf, FLASH_WRITE_SIZE);
+		memset(&write_buf[write_buf_pos], 0, WRITE_BUF_SIZE - write_buf_pos);
+		write(HEADER_SIZE + write_pos, write_buf, WRITE_BUF_SIZE);
 		write_pos += write_buf_pos;
 	}
 
@@ -252,41 +254,25 @@ static void coredump_nrf_flash_backend_buffer_output(uint8_t *data, size_t size)
 {
 	size_t chunk_size;
 
-	dump_crc = crc16_ccitt(dump_crc, data, size);
-
-	/* If the write buffer is non-empty, append it with new data. */
+	/*
+	 * Write all data using intermediate buffer to assure proper write alignment,
+	 * and to calculate a valid CRC even if the data keeps changing during write
+	 * (for example, if the data is within the IRQ stack region).
+	 */
 
-	if (write_buf_pos > 0) {
-		chunk_size = MIN(size, FLASH_WRITE_SIZE - write_buf_pos);
+	while (size > 0) {
+		chunk_size = MIN(size, WRITE_BUF_SIZE - write_buf_pos);
 		memcpy(&write_buf[write_buf_pos], data, chunk_size);
+		dump_crc = crc16_ccitt(dump_crc, &write_buf[write_buf_pos], chunk_size);
 		write_buf_pos += chunk_size;
 		data += chunk_size;
 		size -= chunk_size;
-	}
-
-	/* Flush the write buffer if it's full. */
-
-	if (write_buf_pos == FLASH_WRITE_SIZE) {
-		write(HEADER_SIZE + write_pos, write_buf, FLASH_WRITE_SIZE);
-		write_pos += write_buf_pos;
-		write_buf_pos = 0;
-	}
-
-	/* Write the remaining full write blocks directly to flash. */
-
-	if (size >= FLASH_WRITE_SIZE) {
-		chunk_size = ROUND_DOWN(size, FLASH_WRITE_SIZE);
-		write(HEADER_SIZE + write_pos, data, chunk_size);
-		write_pos += chunk_size;
-		data += chunk_size;
-		size -= chunk_size;
-	}
 
-	/* Store the remaining data in the write buffer. */
-
-	if (size > 0) {
-		memcpy(write_buf, data, size);
-		write_buf_pos = size;
+		if (write_buf_pos == WRITE_BUF_SIZE) {
+			write(HEADER_SIZE + write_pos, write_buf, WRITE_BUF_SIZE);
+			write_pos += WRITE_BUF_SIZE;
+			write_buf_pos = 0;
+		}
 	}
 }