linux-kernel - [PATCH 6/9] arm64: Make return_address() use arch_stack

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Date:   Wed, 17 Nov 2021 14:07:34 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     aou@...s.berkeley.edu, borntraeger@...ibm.com, bp@...en8.de,
        broonie@...nel.org, catalin.marinas@....com,
        dave.hansen@...ux.intel.com, gor@...ux.ibm.com, hca@...ux.ibm.com,
        linux-kernel@...r.kernel.org, madvenka@...ux.microsoft.com,
        mark.rutland@....com, mhiramat@...nel.org, mingo@...hat.com,
        mpe@...erman.id.au, palmer@...belt.com, paul.walmsley@...ive.com,
        peterz@...radead.org, rostedt@...dmis.org, tglx@...utronix.de,
        will@...nel.org
Subject: [PATCH 6/9] arm64: Make return_address() use arch_stack_walk()

From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>

To enable RELIABLE_STACKTRACE and LIVEPATCH on arm64, we need to
substantially rework arm64's unwinding code. As part of this, we want to
minimize the set of unwind interfaces we expose, and avoid open-coding
of unwind logic outside of stacktrace.c.

Currently return_address() walks the stack of the current task by
calling start_backtrace() with return_address as the PC and the frame
pointer of return_address() as the next frame, iterating unwind steps
using walk_stackframe(). This is functionally equivalent to calling
arch_stack_walk() for the current stack, which will start from its
caller (i.e. return_address()) as the PC and it's caller's frame record
as the next frame.

Make return_address() use arch_stackwalk(). This simplifies
return_address(), and in future will alow us to make walk_stackframe()
private to stacktrace.c.

There should be no functional change as a result of this patch.

Signed-off-by: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
Tested-by: Mark Rutland <mark.rutland@....com>
Reviewed-by: Mark Brown <broonie@...nel.org>
Reviewed-by: Mark Rutland <mark.rutland@....com>
[Mark: elaborate commit message]
Signed-off-by: Mark Rutland <mark.rutland@....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);

 	if (!data.level)
 		return data.addr;
-- 
2.11.0