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From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: broonie@kernel.org, jpoimboe@redhat.com, ardb@kernel.org,
	nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com,
	catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org,
	pasha.tatashin@soleen.com, jthierry@redhat.com,
	linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v8 1/4] arm64: Make all stack walking functions use arch_stack_walk()
Date: Tue, 24 Aug 2021 12:38:25 -0500	[thread overview]
Message-ID: <66d0ff83-bf67-5576-4c74-10f825855091@linux.microsoft.com> (raw)
In-Reply-To: <da2bb980-09c3-5a39-73cd-ca4de4c38d51@linux.microsoft.com>



>>> diff --git a/arch/arm64/kernel/return_address.c b/arch/arm64/kernel/return_address.c
>>> index a6d18755652f..92a0f4d434e4 100644
>>> --- a/arch/arm64/kernel/return_address.c
>>> +++ b/arch/arm64/kernel/return_address.c
>>> @@ -35,15 +35,11 @@ NOKPROBE_SYMBOL(save_return_addr);
>>>  void *return_address(unsigned int level)
>>>  {
>>>  	struct return_address_data data;
>>> -	struct stackframe frame;
>>>  
>>>  	data.level = level + 2;
>>>  	data.addr = NULL;
>>>  
>>> -	start_backtrace(&frame,
>>> -			(unsigned long)__builtin_frame_address(0),
>>> -			(unsigned long)return_address);
>>> -	walk_stackframe(current, &frame, save_return_addr, &data);
>>> +	arch_stack_walk(save_return_addr, &data, current, NULL);
>>>  
>>>  	if (!data.level)
>>>  		return data.addr;
>>
>> Nor that arch_stack_walk() will start with it's caller, so
>> return_address() will be included in the trace where it wasn't
>> previously, which implies we need to skip an additional level.
>>
> 
> You are correct. I will fix this. Thanks for catching this.
> 
>> That said, I'm not entirely sure why we need to skip 2 levels today; it
>> might be worth checking that's correct.
>>
> 
> AFAICT, return_address() acts like builtin_return_address(). That is, it
> returns the address of the caller. If func() calls return_address(),
> func() wants its caller's address. So, return_address() and func() need to
> be skipped.
> 
> I will change it to skip 3 levels instead of 2.
> 

Actually, I take that back. I remember now. return_address() used to start
with PC=return_address(). That is, it used to start with itself. arch_stack_walk()
starts with its caller which, in this case, is return_address(). So, I don't need
to change anything.

Do you agree?

Madhavan

  reply	other threads:[~2021-08-24 17:40 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <b45aac2843f16ca759e065ea547ab0afff8c0f01>
2021-08-12 19:05 ` [RFC PATCH v8 0/4] arm64: Reorganize the unwinder and implement stack trace reliability checks madvenka
2021-08-12 19:06   ` [RFC PATCH v8 1/4] arm64: Make all stack walking functions use arch_stack_walk() madvenka
2021-08-24 13:13     ` Mark Rutland
2021-08-24 17:21       ` Madhavan T. Venkataraman
2021-08-24 17:38         ` Madhavan T. Venkataraman [this message]
2021-08-24 17:38         ` Mark Brown
2021-08-24 17:40           ` Madhavan T. Venkataraman
2021-08-26  4:52       ` Madhavan T. Venkataraman
2021-10-09 23:41       ` Madhavan T. Venkataraman
2021-08-12 19:06   ` [RFC PATCH v8 2/4] arm64: Reorganize the unwinder code for better consistency and maintenance madvenka
2021-08-26 15:46     ` Mark Brown
2021-08-26 23:19       ` Madhavan T. Venkataraman
2021-09-01 16:20         ` Mark Brown
2021-09-02  7:10           ` Madhavan T. Venkataraman
2021-08-12 19:06   ` [RFC PATCH v8 3/4] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-08-24  5:55     ` nobuta.keiya
2021-08-24 12:19       ` Madhavan T. Venkataraman
2021-08-25  0:01         ` nobuta.keiya
2021-08-26 15:57     ` Mark Brown
2021-08-26 23:31       ` Madhavan T. Venkataraman
2021-08-12 19:06   ` [RFC PATCH v8 4/4] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-08-12 19:17   ` [RFC PATCH v8 0/4] arm64: Reorganize the unwinder and implement stack trace reliability checks Madhavan T. Venkataraman

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