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From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: mark.rutland@arm.com, broonie@kernel.org, jthierry@redhat.com,
	catalin.marinas@arm.com, will@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 1/1] arm64: Implement stack trace termination record
Date: Sun, 4 Apr 2021 11:29:57 -0500	[thread overview]
Message-ID: <74475382-9482-48ac-e9a3-00073cb721ea@linux.microsoft.com> (raw)
In-Reply-To: <49790505-f611-b4a2-c804-b779060601a9@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

  reply	other threads:[~2021-04-04 16:30 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <659f3d5cc025896ba4c49aea431aa8b1abc2b741>
2021-04-02  3:24 ` [RFC PATCH v2 0/1] " madvenka
2021-04-02  3:24   ` [RFC PATCH v2 1/1] " madvenka
2021-04-03 15:59     ` Josh Poimboeuf
2021-04-04  3:46       ` Madhavan T. Venkataraman
2021-04-04  4:40         ` Madhavan T. Venkataraman
2021-04-04 16:29           ` Madhavan T. Venkataraman [this message]
2021-04-14 12:09     ` Madhavan T. Venkataraman
2021-04-16 16:17     ` Mark Brown
2021-04-16 17:31       ` Madhavan T. Venkataraman
2021-04-19 18:16   ` [RFC PATCH v2 0/1] " Madhavan T. Venkataraman
2021-04-19 18:18     ` Madhavan T. Venkataraman

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