break from long loops on shutdown request

In loops that typically take longer time to complete, check if there is
a pending shutdown request. If so, terminate the loop.

This allows to respond to a signal requesting a shutdown during some
loops which do not return control to main OpenOCD loop.

Change-Id: Iace0b58eddde1237832d0f9333a7c7b930565674
Signed-off-by: Evgeniy Naydanov <evgeniy.naydanov@syntacore.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8032
Reviewed-by: Jan Matyas <jan.matyas@codasip.com>
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/image.c

@@ -24,6 +24,7 @@
 #include "image.h"
 #include "target.h"
 #include <helper/log.h>
+#include <server/server.h>
 
 /* convert ELF header field to host endianness */
 #define field16(elf, field) \
@@ -1295,6 +1296,8 @@ int image_calculate_checksum(const uint8_t *buffer, uint32_t nbytes, uint32_t *c
 			crc = (crc << 8) ^ crc32_table[((crc >> 24) ^ *buffer++) & 255];
 		}
 		keep_alive();
+		if (openocd_is_shutdown_pending())
+			return ERROR_SERVER_INTERRUPTED;
 	}
 
 	LOG_DEBUG("Calculating checksum done; checksum=0x%" PRIx32, crc);