[3.16.y-ckt stable] Patch "Revert "ARM64: unwind: Fix PC calculation"" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    Revert "ARM64: unwind: Fix PC calculation"

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt20.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 65e390f703eeec216f11a6c78bab81c8dce9afb2 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon at arm.com>
Date: Wed, 28 Oct 2015 16:56:13 +0000
Subject: Revert "ARM64: unwind: Fix PC calculation"

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 at arm.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.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;
 }