[PATCH] ARM: NOMMU: Fix exc_ret for stack frame type

[Jisheng Zhang]

commit 72cd4064fcca ("ARM: 8830/1: NOMMU: Toggle only bits in
EXC_RETURN we are really care of") only sets BIT[3] for Thread mode
and BIT[2] for PSP, it leaves BIT[4] untouched. But there's such a
case: the pre-linux env makes use of FPU then the BIT[4] in 'lr' is
cleared, this brings an umatch issue since the NOMMU kernel doesn't
support FPU yet. Before the above commit, we hardcode the exc_ret
as 0xfffffffd, so the flow works fine.

Fix this issue by explicitly set BIT[4] which means using standard
stack frame.

Fixes: 72cd4064fcca ("ARM: 8830/1: NOMMU: Toggle only bits in EXC_RETURN we are really care of")
Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
---
 arch/arm/include/asm/v7m.h | 1 +
 arch/arm/mm/proc-v7m.S     | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/arm/include/asm/v7m.h b/arch/arm/include/asm/v7m.h
index 4512f7e1918f..3aea6d3c97ee 100644
--- a/arch/arm/include/asm/v7m.h
+++ b/arch/arm/include/asm/v7m.h
@@ -51,6 +51,7 @@
  */
 #define EXC_RET_STACK_MASK			0x00000004
 #define EXC_RET_THREADMODE_PROCESSSTACK		(3 << 2)
+#define EXC_RET_FTYPE				(1 << 4)
 
 /* Cache related definitions */
 
diff --git a/arch/arm/mm/proc-v7m.S b/arch/arm/mm/proc-v7m.S
index ed7781c84341..fdae077d2654 100644
--- a/arch/arm/mm/proc-v7m.S
+++ b/arch/arm/mm/proc-v7m.S
@@ -138,6 +138,7 @@ __v7m_setup_cont:
 1:	cpsid	i
 	/* Calculate exc_ret */
 	orr	r10, lr, #EXC_RET_THREADMODE_PROCESSSTACK
+	orr	r10, #EXC_RET_FTYPE
 	ldmia	sp, {r0-r3, r12}
 	str	r5, [r12, #11 * 4]	@ restore the original SVC vector entry
 	mov	lr, r6			@ restore LR
-- 
2.45.2