linux-kernel - [PATCH 3.16 264/370] ARC: [arcompact] handle unaligned access delay slot corner case

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Message-ID: <lsq.1489146383.941954704@decadent.org.uk>
Date:   Fri, 10 Mar 2017 11:46:23 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Vineet Gupta" <vgupta@...opsys.com>
Subject: [PATCH 3.16 264/370] ARC: [arcompact] handle unaligned access
 delay slot corner case

3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Vineet Gupta <vgupta@...opsys.com>

commit 9aed02feae57bf7a40cb04ea0e3017cb7a998db4 upstream.

After emulating an unaligned access in delay slot of a branch, we
pretend as the delay slot never happened - so return back to actual
branch target (or next PC if branch was not taken).

Curently we did this by handling STATUS32.DE, we also need to clear the
BTA.T bit, which is disregarded when returning from original misaligned
exception, but could cause weirdness if it took the interrupt return
path (in case interrupt was acive too)

One ARC700 customer ran into this when enabling unaligned access fixup
for kernel mode accesses as well

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arc/kernel/unaligned.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/arc/kernel/unaligned.c
+++ b/arch/arc/kernel/unaligned.c
@@ -240,8 +240,9 @@ int misaligned_fixup(unsigned long addre
 	if (state.fault)
 		goto fault;
 
+	/* clear any remanants of delay slot */
 	if (delay_mode(regs)) {
-		regs->ret = regs->bta;
+		regs->ret = regs->bta ~1U;
 		regs->status32 &= ~STATUS_DE_MASK;
 	} else {
 		regs->ret += state.instr_len;