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

["Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>]

On 4/3/21 11:40 PM, Madhavan T. Venkataraman wrote:
> 
> 
> 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.
> 

Again, I apologize. I had this confused with something else in my notes.

So, the stack trace looks like this without my changes to convert the branch to
secondary_start_kernel() to a call:

		 ...
[    0.022492]   secondary_start_kernel+0x188/0x1e0
[    0.022503]   0xf8689e1cc

It looks like the code calls __enable_mmu before reaching the place where it
branches to secondary_start_kernel().

	bl      __enable_mmu

The return address register should be set to the next instruction address. I am
guessing that the return address is 0xf8689e1cc because of the idmap stuff.

Madhavan