cortex_m: fix scan-build false positive

Scan-build is unable to detect that 'target->dbg_msg_enabled' does
not change across the function cortex_m_fast_read_all_regs().
It incorrectly assumes that it can be false at the first check (so
'dcrdr' get not assigned) and it is true later on (when 'dcrdr'
get used).
This triggers a false positive:
	src/target/cortex_m.c:338:12: warning:
		3rd function call argument is an uninitialized value
		[core.CallAndMessage]
	retval = mem_ap_write_atomic_u32(armv7m->debug_ap, DCB_DCRDR, dcrdr);

Use a local variable for 'target->dbg_msg_enabled' so scan-build
can track it as not modified.
While there, change the type of 'target->dbg_msg_enabled' to
boolean as there is no reason to use uint32_t.

Change-Id: Icaf1a1b2dea8bc55108182ea440708ab76396cd7
Signed-off-by: Antonio Borneo <[email protected]>
Reviewed-on: https://review.openocd.org/c/openocd/+/8391
Tested-by: jenkins
Reviewed-by: Tomas Vanek <[email protected]>

src/target/cortex_m.c

@@ -279,7 +279,8 @@ static int cortex_m_fast_read_all_regs(struct target *target)
 
 	/* because the DCB_DCRDR is used for the emulated dcc channel
 	 * we have to save/restore the DCB_DCRDR when used */
-	if (target->dbg_msg_enabled) {
+	bool dbg_msg_enabled = target->dbg_msg_enabled;
+	if (dbg_msg_enabled) {
 		retval = mem_ap_read_u32(armv7m->debug_ap, DCB_DCRDR, &dcrdr);
 		if (retval != ERROR_OK)
 			return retval;
@@ -332,7 +333,7 @@ static int cortex_m_fast_read_all_regs(struct target *target)
 	if (retval != ERROR_OK)
 		return retval;
 
-	if (target->dbg_msg_enabled) {
+	if (dbg_msg_enabled) {
 		/* restore DCB_DCRDR - this needs to be in a separate
 		 * transaction otherwise the emulated DCC channel breaks */
 		retval = mem_ap_write_atomic_u32(armv7m->debug_ap, DCB_DCRDR, dcrdr);

src/target/target.c

@@ -5813,7 +5813,7 @@ static int target_create(struct jim_getopt_info *goi)
 	}
 
 	target->dbgmsg          = NULL;
-	target->dbg_msg_enabled = 0;
+	target->dbg_msg_enabled = false;
 
 	target->endianness = TARGET_ENDIAN_UNKNOWN;
 

src/target/target.h

@@ -160,7 +160,7 @@ struct target {
 	struct watchpoint *watchpoints;		/* list of watchpoints */
 	struct trace *trace_info;			/* generic trace information */
 	struct debug_msg_receiver *dbgmsg;	/* list of debug message receivers */
-	uint32_t dbg_msg_enabled;			/* debug message status */
+	bool dbg_msg_enabled;				/* debug message status */
 	void *arch_info;					/* architecture specific information */
 	void *private_config;				/* pointer to target specific config data (for jim_configure hook) */
 	struct target *next;				/* next target in list */

src/target/target_request.c

@@ -164,7 +164,7 @@ static int add_debug_msg_receiver(struct command_context *cmd_ctx, struct target
 	(*p)->next = NULL;
 
 	/* enable callback */
-	target->dbg_msg_enabled = 1;
+	target->dbg_msg_enabled = true;
 
 	return ERROR_OK;
 }
@@ -225,7 +225,7 @@ int delete_debug_msg_receiver(struct command_context *cmd_ctx, struct target *ta
 				free(c);
 				if (!*p) {
 					/* disable callback */
-					target->dbg_msg_enabled = 0;
+					target->dbg_msg_enabled = false;
 				}
 				return ERROR_OK;
 			} else