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From: "tomas.vanek at fbl dot cz" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug gdb/28549] ARM/Cortex-M: improper stack unwinding when the
 target is in lockup state
Date: Fri, 10 Dec 2021 12:30:35 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D28549

tomas.vanek at fbl dot cz changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tomas.vanek at fbl dot cz

--- Comment #14 from tomas.vanek at fbl dot cz ---
Fredrik,

I'm afraid that simply adding lockup addresses to the list of magic address=
 is
not correct. The Cortex-M lockup differs from an exception! The lockup does=
 not
stack anything, it just sets PC (and other special regs). So there is no po=
int
in trying to unwind lockup frame. It does not seem possible, the previous P=
C is
lost.

Unwinding lockup state as it was an exception may result again in peeking n=
ot
existing memory (arm_m_exception_cache() reads word @ unwound_sp + 28)

So I would recommend splitting arm_m_addr_is_magic() to
arm_m_addr_is_exc_return()
and arm_m_addr_is_lockup().
Then introduce another Cortex-M specific unwinder "arm m lockup" with a tri=
vial
implementation:
arm_m_lockup_this_id() will always return outer_frame_id
and
arm_m_lockup_unwind_sniffer() will check PC for arm_m_addr_is_lockup()

Tom

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