From 9d4de283d55013257f5badba1787778ec941549e Mon Sep 17 00:00:00 2001
From: Andrew Turner <andrew@FreeBSD.org>
Date: Tue, 1 Dec 2015 12:37:04 +0000
Subject: [PATCH] Rework the exception entry/return functions to make them
 valid frames to be unwound through. For this we need the frame pointer (x29)
 to point to the location on the stack where we stored the previous frame
 pointer, and link register. To simplify this the stack pointer is only
 adjusted by addition and subtraction, and not through the use of post
 increment on loads and stores.

The updated frame layout is:

+------------+
| lr -- x30  |
+------------+
| fp -- x29  | <-- x29 points at this
+------------+
| Trap frame |
| ...        |
|            | <-- sp points at this
+------------+

The only difference is the first two items, and setting of x29.

Sponsored by:	ABT Systems Ltd
---
 sys/arm64/arm64/exception.S | 77 ++++++++++++++++++++-----------------
 sys/arm64/arm64/genassym.c  |  3 ++
 2 files changed, 44 insertions(+), 36 deletions(-)

diff --git a/sys/arm64/arm64/exception.S b/sys/arm64/arm64/exception.S
index 279f34f4804c..9ca9685ff36e 100644
--- a/sys/arm64/arm64/exception.S
+++ b/sys/arm64/arm64/exception.S
@@ -37,29 +37,32 @@ __FBSDID("$FreeBSD$");
 	mov	x18, sp
 	sub	sp, sp, #128
 .endif
-	stp	x28, x29, [sp, #-16]!
-	stp	x26, x27, [sp, #-16]!
-	stp	x24, x25, [sp, #-16]!
-	stp	x22, x23, [sp, #-16]!
-	stp	x20, x21, [sp, #-16]!
-	stp	x18, x19, [sp, #-16]!
-	stp	x16, x17, [sp, #-16]!
-	stp	x14, x15, [sp, #-16]!
-	stp	x12, x13, [sp, #-16]!
-	stp	x10, x11, [sp, #-16]!
-	stp	x8, x9, [sp, #-16]!
-	stp	x6, x7, [sp, #-16]!
-	stp	x4, x5, [sp, #-16]!
-	stp	x2, x3, [sp, #-16]!
-	stp	x0, x1, [sp, #-16]!
+	sub	sp, sp, #(TF_SIZE + 16)
+	stp	x29, x30, [sp, #(TF_SIZE)]
+	stp	x28, x29, [sp, #(TF_X + 28 * 8)]
+	stp	x26, x27, [sp, #(TF_X + 26 * 8)]
+	stp	x24, x25, [sp, #(TF_X + 24 * 8)]
+	stp	x22, x23, [sp, #(TF_X + 22 * 8)]
+	stp	x20, x21, [sp, #(TF_X + 20 * 8)]
+	stp	x18, x19, [sp, #(TF_X + 18 * 8)]
+	stp	x16, x17, [sp, #(TF_X + 16 * 8)]
+	stp	x14, x15, [sp, #(TF_X + 14 * 8)]
+	stp	x12, x13, [sp, #(TF_X + 12 * 8)]
+	stp	x10, x11, [sp, #(TF_X + 10 * 8)]
+	stp	x8,  x9,  [sp, #(TF_X + 8  * 8)]
+	stp	x6,  x7,  [sp, #(TF_X + 6  * 8)]
+	stp	x4,  x5,  [sp, #(TF_X + 4  * 8)]
+	stp	x2,  x3,  [sp, #(TF_X + 2  * 8)]
+	stp	x0,  x1,  [sp, #(TF_X + 0  * 8)]
 	mrs	x10, elr_el1
 	mrs	x11, spsr_el1
 .if \el == 0
 	mrs	x18, sp_el0
 .endif
-	stp	x10, x11, [sp, #-16]!
-	stp	x18, lr, [sp, #-16]!
+	stp	x10, x11, [sp, #(TF_ELR)]
+	stp	x18,  lr, [sp, #(TF_SP)]
 	mrs	x18, tpidr_el1
+	add	x29, sp, #(TF_SIZE)
 .endm
 
 .macro	restore_registers el
@@ -70,33 +73,35 @@ __FBSDID("$FreeBSD$");
 	 * handler.  For EL0 exceptions, do_ast already did this.
 	 */
 .endif
-	ldp	x18, lr, [sp], #16
-	ldp	x10, x11, [sp], #16
+	ldp	x18,  lr, [sp, #(TF_SP)]
+	ldp	x10, x11, [sp, #(TF_ELR)]
 .if \el == 0
 	msr	sp_el0, x18
 .endif
 	msr	spsr_el1, x11
 	msr	elr_el1, x10
-	ldp	x0, x1, [sp], #16
-	ldp	x2, x3, [sp], #16
-	ldp	x4, x5, [sp], #16
-	ldp	x6, x7, [sp], #16
-	ldp	x8, x9, [sp], #16
-	ldp	x10, x11, [sp], #16
-	ldp	x12, x13, [sp], #16
-	ldp	x14, x15, [sp], #16
-	ldp	x16, x17, [sp], #16
+	ldp	x0,  x1,  [sp, #(TF_X + 0  * 8)]
+	ldp	x2,  x3,  [sp, #(TF_X + 2  * 8)]
+	ldp	x4,  x5,  [sp, #(TF_X + 4  * 8)]
+	ldp	x6,  x7,  [sp, #(TF_X + 6  * 8)]
+	ldp	x8,  x9,  [sp, #(TF_X + 8  * 8)]
+	ldp	x10, x11, [sp, #(TF_X + 10 * 8)]
+	ldp	x12, x13, [sp, #(TF_X + 12 * 8)]
+	ldp	x14, x15, [sp, #(TF_X + 14 * 8)]
+	ldp	x16, x17, [sp, #(TF_X + 16 * 8)]
 .if \el == 0
-	ldp	x18, x19, [sp], #16
+	ldp	x18, x19, [sp, #(TF_X + 18 * 8)]
 .else
-	ldp	xzr, x19, [sp], #16
+	ldr	     x19, [sp, #(TF_X + 19 * 8)]
 .endif
-	ldp	x20, x21, [sp], #16
-	ldp	x22, x23, [sp], #16
-	ldp	x24, x25, [sp], #16
-	ldp	x26, x27, [sp], #16
-	ldp	x28, x29, [sp], #16
-.if \el == 1
+	ldp	x20, x21, [sp, #(TF_X + 20 * 8)]
+	ldp	x22, x23, [sp, #(TF_X + 22 * 8)]
+	ldp	x24, x25, [sp, #(TF_X + 24 * 8)]
+	ldp	x26, x27, [sp, #(TF_X + 26 * 8)]
+	ldp	x28, x29, [sp, #(TF_X + 28 * 8)]
+.if \el == 0
+	add	sp, sp, #(TF_SIZE + 16)
+.else
 	mov	sp, x18
 	mrs	x18, tpidr_el1
 .endif
diff --git a/sys/arm64/arm64/genassym.c b/sys/arm64/arm64/genassym.c
index f8dfedab83a5..214b99d727d6 100644
--- a/sys/arm64/arm64/genassym.c
+++ b/sys/arm64/arm64/genassym.c
@@ -60,4 +60,7 @@ ASSYM(TD_PCB, offsetof(struct thread, td_pcb));
 ASSYM(TD_FLAGS, offsetof(struct thread, td_flags));
 ASSYM(TD_LOCK, offsetof(struct thread, td_lock));
 
+ASSYM(TF_SIZE, sizeof(struct trapframe));
+ASSYM(TF_SP, offsetof(struct trapframe, tf_sp));
+ASSYM(TF_ELR, offsetof(struct trapframe, tf_elr));
 ASSYM(TF_X, offsetof(struct trapframe, tf_x));