linux-kernel - [PATCH 3.16.y-ckt 74/94] Revert "ARM64: unwind: Fix PC calculation"

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Date:	Fri, 13 Nov 2015 10:10:08 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Will Deacon <will.deacon@....com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 74/94] Revert "ARM64: unwind: Fix PC calculation"

3.16.7-ckt20 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Will Deacon <will.deacon@....com>

commit 9702970c7bd3e2d6fecb642a190269131d4ac16c upstream.

This reverts commit e306dfd06fcb44d21c80acb8e5a88d55f3d1cf63.

With this patch applied, we were the only architecture making this sort
of adjustment to the PC calculation in the unwinder. This causes
problems for ftrace, where the PC values are matched against the
contents of the stack frames in the callchain and fail to match any
records after the address adjustment.

Whilst there has been some effort to change ftrace to workaround this,
those patches are not yet ready for mainline and, since we're the odd
architecture in this regard, let's just step in line with other
architectures (like arch/arm/) for now.

Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 arch/arm64/kernel/stacktrace.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 55437ba1f5a4..54122c4fd19a 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -48,11 +48,7 @@ int notrace unwind_frame(struct stackframe *frame)

 	frame->sp = fp + 0x10;
 	frame->fp = *(unsigned long *)(fp);
-	/*
-	 * -4 here because we care about the PC at time of bl,
-	 * not where the return will go.
-	 */
-	frame->pc = *(unsigned long *)(fp + 8) - 4;
+	frame->pc = *(unsigned long *)(fp + 8);

 	return 0;
 }
--
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