/*
 * Copyright 2014-2015, Imagination Technologies Limited and/or its
 *                      affiliated group companies.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holder nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
*/


/* ************ PLEASE READ ME !!!!  ****************

	This file is a copy of the mips_excpt_entry.S from $MIPS_ELF_ROOT/share/mips/hal
	(from the 2016.05-03 version) with a single modification, we add a global flag
	'__exception_restore' so we can jump to the restore code sequence from C.

	Future toolchain versions will have this change included and this file will
	be no longer needed.

	Note the above copyright/license is 3 Clause BSD and as such is compatible with LGPLv2.1
	as such we grant licensing this file under LGPLv2.1 (See the file LICENSE in the top level
	directory for more details) as well.

	Thanks for reading.
*/


# Keep each function in a separate named section
#define _FUNCTION_SECTIONS_
.set nomips16

#include <mips/asm.h>
#include <mips/regdef.h>
#include <mips/cpu.h>
#include <mips/hal.h>

# Context size, adjusted for ABI parameter area
#define ADJ (NARGSAVE * SZARG)
# Round up to 16-byte boundary (maximum stack alignment required for any
# supported ABI)
#define CTX_SIZEROUND ((CTX_SIZE + ALSZ) & ALMASK)
#define CTX_SIZEADJ (CTX_SIZEROUND + ADJ)

#define e_ISR	s1
#define e_CR	s3
#define e_BADV	s4
#define e_SR	s5
#define e_EPC	s6
#define e_RA	s7

# DESCRIPTION: Exception entry point. This is small because it must go at
#			   EBASE+0x180. It saves enough context to chain onwards to
#			   __exception_save.
#
LEAF(__exception_entry)
	.set	push
	.set	noat
.weak   _mips_tlb_refill
	_mips_tlb_refill = __exception_save
__tlb_refill_loop:
	# Support an alternative entry point at the start of the exception
	# vector.  Since the exception vector is normally placed first
	# in the link map this allows a user to start execution from the
	# same address that an executable is loaded to.
	LA	k1, __first_boot
	lw	k1, 0(k1)
	beqz	k1, 1f
	# The start code is responsible for clearing __first_boot prior
	# to installing the exception handlers.
	j	_start
1:
	LA	k1, _mips_tlb_refill
	beqz	k1, __tlb_refill_loop
	jr	k1

	.org 0x80
.weak   _mips_xtlb_refill
	_mips_xtlb_refill = __exception_save
__xtlb_refill_loop:
	LA	k1, _mips_xtlb_refill
	beqz	k1, __xtlb_refill_loop
	jr	k1

	.org 0x100
.weak   _mips_cache_error
__cache_error_loop:
	LA	k1, _mips_cache_error
	beqz	k1, __cache_error_loop
	jr	k1

	.org 0x180
	# Free up k1, defering sp adjustment until later
	REG_S	k1, (-CTX_SIZEROUND + CTX_K1)(sp)

	# Use k1 to invoke __exception_save
	LA	k1, _mips_general_exception
	jr	k1
	.set    pop
END(__exception_entry)

#
# FUNCTION:	__exception_save
#
# DESCRIPTION: Exception context save. Save the context, then fake up a call
#              frame.
#
ANESTED(__exception_save, _mips_general_exception, CTX_SIZEADJ, zero)
	.globl  __exception_save;
    .globl  __exception_restore;
	.set	push
	.set	noat

	# k1 is already saved, so use it to save the users sp
	move	k1, sp
	# Finally adjust sp
	PTR_ADDU sp, sp, -CTX_SIZEADJ	# This should be picked up by the backtracer

	# Save context
	REG_S	$1, CTX_REG(1) + ADJ(sp)
	REG_S	$2, CTX_REG(2) + ADJ(sp)
	REG_S	$3, CTX_REG(3) + ADJ(sp)
	REG_S	$4, CTX_REG(4) + ADJ(sp)
	REG_S	$5, CTX_REG(5) + ADJ(sp)
	REG_S	$6, CTX_REG(6) + ADJ(sp)
	REG_S	$7, CTX_REG(7) + ADJ(sp)
	REG_S	$8, CTX_REG(8) + ADJ(sp)
	REG_S	$9, CTX_REG(9) + ADJ(sp)
	REG_S	$10, CTX_REG(10) + ADJ(sp)
	REG_S	$11, CTX_REG(11) + ADJ(sp)
	REG_S	$12, CTX_REG(12) + ADJ(sp)
	REG_S	$13, CTX_REG(13) + ADJ(sp)
	REG_S	$14, CTX_REG(14) + ADJ(sp)
	REG_S	$15, CTX_REG(15) + ADJ(sp)
	REG_S	$16, CTX_REG(16) + ADJ(sp)
	REG_S	$17, CTX_REG(17) + ADJ(sp)
	REG_S	$18, CTX_REG(18) + ADJ(sp)
	REG_S	$19, CTX_REG(19) + ADJ(sp)
	REG_S	$20, CTX_REG(20) + ADJ(sp)
	REG_S	$21, CTX_REG(21) + ADJ(sp)
	REG_S	$22, CTX_REG(22) + ADJ(sp)
	REG_S	$23, CTX_REG(23) + ADJ(sp)
	REG_S	$24, CTX_REG(24) + ADJ(sp)
	REG_S	$25, CTX_REG(25) + ADJ(sp)
	REG_S	$26, CTX_REG(26) + ADJ(sp)
	# k1/$27 has already been saved
	REG_S	$28, CTX_REG(28) + ADJ(sp)
	REG_S	k1, CTX_REG(29) + ADJ(sp) # Use saved sp from earlier
	REG_S	$30, CTX_REG(30) + ADJ(sp)
	REG_S	$31, CTX_REG(31) + ADJ(sp)
	PTR_S	$0, CTX_LINK + ADJ(sp) # Clear the link field

#if (__mips_isa_rev < 6)
	mfhi	$9
	mflo	$10
	REG_S	$9, CTX_HI0 + ADJ(sp)
	REG_S	$10, CTX_LO0 + ADJ(sp)
#endif

	# Trick the backtracer into stepping back to the point where the exception
	# occurred.
	PTR_MFC0 ra, C0_EPC
	mfc0	e_CR, C0_CR
	REG_S	ra, CTX_EPC + ADJ(sp)

	# Finish storing the rest of the CP0 registers
	PTR_MFC0 $9, C0_BADVADDR
	REG_S	$9, CTX_BADVADDR + ADJ(sp)
	sw	e_CR, CTX_CAUSE + ADJ(sp)

	move	$11, $0
	move	$12, $0
	mfc0	$9, C0_CONFIG3
	ext	$10, $9, CFG3_BP_SHIFT, 1
	beqz	$10, 1f
	mfc0	$11, C0_BADPINSTR
1:
	ext	$9, $9, CFG3_BI_SHIFT, 1
	beqz	$9, 1f
	mfc0	$12, C0_BADINSTR
1:
	sw	$11, CTX_BADPINSTR + ADJ(sp)
	sw	$12, CTX_BADINSTR + ADJ(sp)

	# Start computing the address of the context for a0
	move	a0, sp

	# Clear EXL.  Exceptions can now nest.
	mfc0	e_SR, C0_SR
	sw	e_SR, CTX_STATUS + ADJ(sp)
	lui	$9, %hi(~SR_EXL)
	addiu	$9, $9, %lo(~SR_EXL)
	and	e_SR, e_SR, $9
	mtc0	e_SR, C0_SR

	# Manually set up the return address to restore the context below
	LA	ra, __exception_restore
	# Extract the cause code
	and	a1, e_CR, CR_XMASK

	# Finish computing the address of the context for a0
	addiu	a0, a0, ADJ

	# Shift exception number down into expected range
	srl	a1, a1, 2

	# Call the handler, indirect through t9 albeit not for any specific
	# reason
	LA	t9, _mips_handle_exception
	jr	t9

# Return point from handler
# Load context
# now a function on its own, note save code just falls through.


__exception_restore:

#if (__mips_isa_rev < 6)
	REG_L	$9, CTX_HI0 + ADJ(sp)
	REG_L	$10, CTX_LO0 + ADJ(sp)
	mthi	$9
	mtlo	$10
#endif

	REG_L	$1, CTX_REG(1) + ADJ(sp)
	REG_L	$2, CTX_REG(2) + ADJ(sp)
	REG_L	$3, CTX_REG(3) + ADJ(sp)
	REG_L	$4, CTX_REG(4) + ADJ(sp)
	REG_L	$5, CTX_REG(5) + ADJ(sp)
	REG_L	$6, CTX_REG(6) + ADJ(sp)
	REG_L	$7, CTX_REG(7) + ADJ(sp)
	REG_L	$8, CTX_REG(8) + ADJ(sp)
	REG_L	$9, CTX_REG(9) + ADJ(sp)
	REG_L	$10, CTX_REG(10) + ADJ(sp)
	REG_L	$11, CTX_REG(11) + ADJ(sp)
	REG_L	$12, CTX_REG(12) + ADJ(sp)
	REG_L	$13, CTX_REG(13) + ADJ(sp)
	REG_L	$14, CTX_REG(14) + ADJ(sp)
	REG_L	$15, CTX_REG(15) + ADJ(sp)
	REG_L	$16, CTX_REG(16) + ADJ(sp)
	REG_L	$17, CTX_REG(17) + ADJ(sp)
	REG_L	$18, CTX_REG(18) + ADJ(sp)
	REG_L	$19, CTX_REG(19) + ADJ(sp)
	REG_L	$20, CTX_REG(20) + ADJ(sp)
	REG_L	$21, CTX_REG(21) + ADJ(sp)
	REG_L	$22, CTX_REG(22) + ADJ(sp)
	REG_L	$23, CTX_REG(23) + ADJ(sp)
	REG_L	$24, CTX_REG(24) + ADJ(sp)
	REG_L	$25, CTX_REG(25) + ADJ(sp)
	# $26/K0 and $27/K1 are restored with interrupts disabled
	REG_L	$28, CTX_REG(28) + ADJ(sp)
	# $29/SP is restored last
	REG_L	$30, CTX_REG(30) + ADJ(sp)
	REG_L	$31, CTX_REG(31) + ADJ(sp)
	di
	lw	k0, CTX_STATUS + ADJ(sp)
	REG_L	k1, CTX_EPC + ADJ(sp)
	mtc0	k0, C0_SR
	PTR_MTC0 k1, C0_EPC
	ehb
	REG_L	k0, CTX_K0 + ADJ(sp)
	REG_L	k1, CTX_K1 + ADJ(sp)
	REG_L	sp, CTX_SP + ADJ(sp)
	# Return from exception
	eret
	.set	pop
END(__exception_save)