If a Cortex-M MCU become unresponsive during a debug session and
re-examination fails to find MEM-AP, debug_ap pointer is set to NULL.
Eventual call of cortex_m_poll() dereferences debug_ap.
Check debug_ap validity at the begin of cortex_m_poll().
Change-Id: I9519f48760c91a48a9e5e8c34634d247098cb14a
Fixes: 35a503b08d14 (arm_adi_v5: add ap refcount and add get/put around ap use)
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/7108
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
struct cortex_m_common *cortex_m = target_to_cm(target);
struct armv7m_common *armv7m = &cortex_m->armv7m;
+ /* Check if debug_ap is available to prevent segmentation fault.
+ * If the re-examination after an error does not find a MEM-AP
+ * (e.g. the target stopped communicating), debug_ap pointer
+ * can suddenly become NULL.
+ */
+ if (!armv7m->debug_ap) {
+ target->state = TARGET_UNKNOWN;
+ return ERROR_TARGET_NOT_EXAMINED;
+ }
+
/* Read from Debug Halting Control and Status Register */
retval = cortex_m_read_dhcsr_atomic_sticky(target);
if (retval != ERROR_OK) {