[Bug gdb/28549] ARM/Cortex-M: improper stack unwinding when the target is in lockup state

["fredrik.hederstierna@securitas-direct.com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=28549

--- Comment #4 from Fredrik Hederstierna <fredrik.hederstierna@securitas-direct.com> ---
I agree it might be some mixups between LR and PC, though I think in practice
it might not cause any problems in these cases.

To cover also Cortex-M33 ARMv8M maybe also check for LR=0xFFFFFFFE and
PC=0xEFFFFFFE. The 'easy' fix is to add these values I guess:

diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index 857a52a9a51..33b03ead5a4 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -556,6 +556,13 @@ arm_m_addr_is_magic (CORE_ADDR addr)
       case 0xfffffff1:
       case 0xfffffff9:
       case 0xfffffffd:
+      /* Values for Lockup state.
+       For more details see "B1.5.15 Unrecoverable exception cases" in
+       both ARMv6-M and ARMv7-M Architecture Reference Manuals, or
+        see "B4.32 Lockup" in ARMv8-M Architecture Reference Manual.  */
+      case 0xeffffffe:
+      case 0xfffffffe:
+      case 0xffffffff:
        /* Address is magic.  */
        return 1;

Though maybe we would like to add some more info that actually detects more
explicit the LOCKUP state and make some printouts about that?

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