Re: [RFC PATCH v2 1/1] arm64: Implement stack trace termination record

[Madhavan T. Venkataraman]

On 4/3/21 10:46 PM, Madhavan T. Venkataraman wrote:
>> I'm somewhat arm-ignorant, so take the following comments with a grain
>> of salt.
>>
>>
>> I don't think changing these to 'bl' is necessary, unless you wanted
>> __primary_switched() and __secondary_switched() to show up in the
>> stacktrace for some reason?  If so, that seems like a separate patch.
>>
> The problem is with __secondary_switched. If you trace the code back to where
> a secondary CPU is started, I don't see any calls anywhere. There are only
> branches if I am not mistaken. So, the return address register never gets
> set up with a proper address. The stack trace shows some hexadecimal value
> instead of a symbol name.
> 

Actually, I take that back. There are calls in that code path. But I did only
see some hexadecimal value instead of a proper address in the stack trace.
Sorry about that confusion.

My reason to convert the branches to calls is this - the value of the return
address register at that point is the return PC of the previous branch and link
instruction wherever that happens to be. I think that is a little arbitrary.

Instead, if I call start_kernel() and secondary_start_kernel(), the return address
gets set up to the next instruction which, IMHO, is better.

But I am open to other suggestions.

Madhavan