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From: Mark Rutland <mark.rutland@arm.com>
To: madvenka@linux.microsoft.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,
	linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v10 04/11] arm64: Make return_address() use arch_stack_walk()
Date: Fri, 22 Oct 2021 19:51:48 +0100	[thread overview]
Message-ID: <20211022185148.GA91654@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20211015025847.17694-5-madvenka@linux.microsoft.com>

On Thu, Oct 14, 2021 at 09:58:40PM -0500, madvenka@linux.microsoft.com wrote:
> From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
> 
> Currently, return_address() in ARM64 code walks the stack using
> start_backtrace() and walk_stackframe(). Make it use arch_stack_walk()
> instead. This makes maintenance easier.
> 
> Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
> ---
>  arch/arm64/kernel/return_address.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> 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);

This looks equivalent to me. Previously the arguments to
start_backtrace() meant that walk_stackframe would report
return_address(), then the caller of return_address(), and so on. As
arch_stack_walk() starts from its immediate caller (i.e.
return_address()), that should result in the same trace.

It would be nice if we could note something to that effect in the commit
message.

I had a play with ftrace, which uses return_address(), and that all
looks sound.

>  
>  	if (!data.level)
>  		return data.addr;

The end of this function currently does:

	if (!data.level)
		return data.addr;
	else
		return NULL;

... but since we initialize data.addr to NULL, and save_return_addr()
only writes to data.addr when called at the correct level, we can
simplify that to:

	return data.addr;

Regardles of that cleanup:

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>

I'll continue reviewing the series next week.

Thanks,
Mark.

  parent reply	other threads:[~2021-10-22 18:52 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <c05ce30dcc9be1bd6b5e24a2ca8fe1d66246980b>
2021-10-15  2:34 ` [PATCH v9 00/11] arm64: Reorganize the unwinder and implement stack trace reliability checks madvenka
2021-10-15  2:34   ` [PATCH v9 01/11] arm64: Select STACKTRACE in arch/arm64/Kconfig madvenka
2021-10-15  2:34   ` [PATCH v9 10/11] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-10-15  2:34   ` [PATCH v9 11/11] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-10-15  2:34   ` [PATCH v9 02/11] arm64: Make perf_callchain_kernel() use arch_stack_walk() madvenka
2021-10-15  2:34   ` [PATCH v9 03/11] arm64: Make get_wchan() " madvenka
2021-10-15  2:34   ` [PATCH v9 04/11] arm64: Make return_address() " madvenka
2021-10-15  2:34   ` [PATCH v9 05/11] arm64: Make dump_stacktrace() " madvenka
2021-10-15  2:34   ` [PATCH v9 06/11] arm64: Make profile_pc() " madvenka
2021-10-15  2:34   ` [PATCH v9 07/11] arm64: Call stack_backtrace() only from within walk_stackframe() madvenka
2021-10-15  2:34   ` [PATCH v9 08/11] arm64: Rename unwinder functions, prevent them from being traced and kprobed madvenka
2021-10-15  2:34   ` [PATCH v9 09/11] arm64: Make the unwind loop in unwind() similar to other architectures madvenka
2021-10-15  2:53   ` [PATCH v9 00/11] arm64: Reorganize the unwinder and implement stack trace reliability checks Madhavan T. Venkataraman
2021-10-15  2:58 ` [PATCH v10 " madvenka
2021-10-15  2:58   ` [PATCH v10 01/11] arm64: Select STACKTRACE in arch/arm64/Kconfig madvenka
2021-10-15 18:28     ` Mark Brown
2021-10-21 12:28       ` Madhavan T. Venkataraman
2021-10-22 18:02     ` Mark Rutland
2021-11-12 17:44       ` Mark Rutland
2021-11-14 16:15         ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 02/11] arm64: Make perf_callchain_kernel() use arch_stack_walk() madvenka
2021-10-20 14:59     ` Mark Brown
2021-10-21 12:28       ` Madhavan T. Venkataraman
2021-10-22 18:11     ` Mark Rutland
2021-10-23 12:49       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 03/11] arm64: Make get_wchan() " madvenka
2021-10-20 16:10     ` Mark Brown
2021-10-21 12:30       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 04/11] arm64: Make return_address() " madvenka
2021-10-20 15:03     ` Mark Brown
2021-10-21 12:29       ` Madhavan T. Venkataraman
2021-10-22 18:51     ` Mark Rutland [this message]
2021-10-23 12:51       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 05/11] arm64: Make dump_stacktrace() " madvenka
2021-10-25 16:49     ` Mark Rutland
2021-10-26 12:05       ` Mark Rutland
2021-10-27 16:09         ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 06/11] arm64: Make profile_pc() " madvenka
2021-10-25  2:18     ` nobuta.keiya
2021-10-27 16:10       ` Madhavan T. Venkataraman
2021-10-27 13:32     ` Mark Rutland
2021-10-27 16:15       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 07/11] arm64: Call stack_backtrace() only from within walk_stackframe() madvenka
2021-10-15  2:58   ` [PATCH v10 08/11] arm64: Rename unwinder functions, prevent them from being traced and kprobed madvenka
2021-10-27 17:53     ` Mark Rutland
2021-10-27 20:07       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 09/11] arm64: Make the unwind loop in unwind() similar to other architectures madvenka
2021-10-15  2:58   ` [PATCH v10 10/11] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-11-04 12:39     ` nobuta.keiya
2021-11-10  3:13       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 11/11] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-10-15 17:00   ` [PATCH v10 00/11] arm64: Reorganize the unwinder and implement stack trace reliability checks Madhavan T. Venkataraman

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