On 10/22/21 1:51 PM, Mark Rutland wrote:

On Thu, Oct 14, 2021 at 09:58:40PM -0500, madvenka@linux.microsoft.com wrote:

quoted

From: "Madhavan T. Venkataraman" <redacted>

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 <redacted>
---
 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.

Will do.

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

Thanks a lot!

quoted

 
 	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;

OK. I will make this change.

Regardles of that cleanup:

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

Thanks a lot!

I'll continue reviewing the series next week.

Great!

Madhavan

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