Exception Stack Frames are not correct in coredumps

[vbrzeski]

Exception Stack Frames are not correct in coredumps

The stack pointer in the Zephyr ARM Coredumps are imprecise due to an error in the stack offset calculation:

zephyr/arch/arm/core/cortex_m/fault.c

Lines 1115 to 1117 in c343890

	#ifdef CONFIG_DEBUG_COREDUMP
	z_arm_coredump_fault_sp = POINTER_TO_UINT(esf);
	#endif

The stackpointer can't be calculated without EXC_RETURN. We don't have a reliable way to calculate it outside of the coredump handler.

I see we have an existing PR that would resolve this issue: PR #73189.

To Reproduce
With an ARM M4 MCU with FPU extension (e.g. nRF52833):

1. have one thread doing floating point math
2. have one thread that doesn't do floating point math
3. grab a few coredumps
4. unwind and symbolicate the coredumps, one will fail to unwind properly

Expected behavior
I expect the SP to be accurate :)

Impact
This prevents us from using upstream Zephyr.

Interesting Docs

• Exception Return Behavior
• Exception Stack Frames
• Stack Alignment

[github-actions]

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[ycsin]

Reopen as #73189 has been reverted