source: mainline/kernel/arch/mips32/src/start.S@ e662a5f

#
# Copyright (c) 2003-2004 Jakub Jermar
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# - Redistributions of source code must retain the above copyright
#   notice, this list of conditions and the following disclaimer.
# - 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.
# - The name of the author may not be used to endorse or promote products
#   derived from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
#

#include <arch/asm/regname.h>
#include <arch/mm/page.h>
#include <arch/asm/boot.h>
#include <arch/context_offset.h>
#include <arch/stack.h>
        
.text

.set noat
.set noreorder
.set nomacro

.global kernel_image_start
.global tlb_refill_entry
.global cache_error_entry
.global exception_entry
.global userspace_asm

# Which status bits should are thread-local
#define REG_SAVE_MASK 0x1f # KSU(UM), EXL, ERL, IE
        
# Save registers to space defined by \r
# We will change status: Disable ERL,EXL,UM,IE
# These changes will be automatically reversed in REGISTER_LOAD
# SP is NOT saved as part of these registers
.macro REGISTERS_STORE_AND_EXC_RESET r
        sw $at, EOFFSET_AT(\r)
        sw $v0, EOFFSET_V0(\r)
        sw $v1, EOFFSET_V1(\r)
        sw $a0, EOFFSET_A0(\r)
        sw $a1, EOFFSET_A1(\r)
        sw $a2, EOFFSET_A2(\r)
        sw $a3, EOFFSET_A3(\r)
        sw $t0, EOFFSET_T0(\r)
        sw $t1, EOFFSET_T1(\r)
        sw $t2, EOFFSET_T2(\r)
        sw $t3, EOFFSET_T3(\r)
        sw $t4, EOFFSET_T4(\r)
        sw $t5, EOFFSET_T5(\r)
        sw $t6, EOFFSET_T6(\r)
        sw $t7, EOFFSET_T7(\r)
        sw $t8, EOFFSET_T8(\r)
        sw $t9, EOFFSET_T9(\r)

        mflo $at
        sw $at, EOFFSET_LO(\r)
        mfhi $at
        sw $at, EOFFSET_HI(\r)
        
        sw $gp, EOFFSET_GP(\r)
        sw $ra, EOFFSET_RA(\r)
        sw $k1, EOFFSET_K1(\r)

        mfc0 $t0, $status
        mfc0 $t1, $epc
        
        and $t2, $t0, REG_SAVE_MASK     # Save only KSU,EXL,ERL,IE
        li $t3, ~(0x1f)
        and $t0, $t0, $t3               # Clear KSU,EXL,ERL,IE
        
        sw $t2,EOFFSET_STATUS(\r)
        sw $t1,EOFFSET_EPC(\r)
        mtc0 $t0, $status
.endm

.macro REGISTERS_LOAD r
        # Update only UM,EXR,IE from status, the rest
        # is controlled by OS and not bound to task
        mfc0 $t0, $status
        lw $t1,EOFFSET_STATUS(\r)

        li $t2, ~REG_SAVE_MASK          # Mask UM,EXL,ERL,IE
        and $t0, $t0, $t2
        
        or $t0, $t0, $t1                # Copy UM,EXL, ERL, IE from saved status
        mtc0 $t0, $status
        
        lw $v0, EOFFSET_V0(\r)
        lw $v1, EOFFSET_V1(\r)
        lw $a0, EOFFSET_A0(\r)
        lw $a1, EOFFSET_A1(\r)
        lw $a2, EOFFSET_A2(\r)
        lw $a3, EOFFSET_A3(\r)
        lw $t0, EOFFSET_T0(\r)
        lw $t1, EOFFSET_T1(\r)
        lw $t2, EOFFSET_T2(\r)
        lw $t3, EOFFSET_T3(\r)
        lw $t4, EOFFSET_T4(\r)
        lw $t5, EOFFSET_T5(\r)
        lw $t6, EOFFSET_T6(\r)
        lw $t7, EOFFSET_T7(\r)
        lw $t8, EOFFSET_T8(\r)
        lw $t9, EOFFSET_T9(\r)
        
        lw $gp, EOFFSET_GP(\r)
        lw $ra, EOFFSET_RA(\r)
        lw $k1, EOFFSET_K1(\r)
        
        lw $at, EOFFSET_LO(\r)
        mtlo $at
        lw $at, EOFFSET_HI(\r)
        mthi $at

        lw $at, EOFFSET_EPC(\r)
        mtc0 $at, $epc
        
        lw $at, EOFFSET_AT(\r)
        lw $sp, EOFFSET_SP(\r)
.endm

# Move kernel stack pointer address to register K0
# - if we are in user mode, load the appropriate stack
# address
.macro KERNEL_STACK_TO_K0
        # If we are in user mode
        mfc0 $k0, $status
        andi $k0, 0x10
        
        beq $k0, $0, 1f
        add $k0, $sp, 0
        
        # Move $k0 pointer to kernel stack
        lui $k0, %hi(supervisor_sp)
        ori $k0, $k0, %lo(supervisor_sp)
        # Move $k0 (superveisor_sp)
        lw $k0, 0($k0)
1:              
.endm
                
.org 0x0
kernel_image_start:
        /* Load temporary stack */
        lui $sp, %hi(end_stack)
        ori $sp, $sp, %lo(end_stack)
        
        /* $a1 contains physical address of bootinfo_t */
        /* $a2 contains size of bootinfo_t */
        
        beq $a2, $0, bootinfo_end
        
        /* Not sure about this, but might be needed for PIC code???? */
        lui $gp, 0x8000
        
        lui $a3, %hi(bootinfo)
        ori $a3, $a3, %lo(bootinfo)
        
        bootinfo_loop:
                
                lw $v0, 0($a1)
                sw $v0, 0($a3)
                
                addi $a1, $a1, 4
                addi $a3, $a3, 4
                addi $a2, $a2, -4
                
                bgtz $a2, bootinfo_loop
                nop
                
        bootinfo_end:
        
        jal arch_pre_main
        nop
        
        j main_bsp
        nop

        .space TEMP_STACK_SIZE
end_stack:

tlb_refill_entry:
        j tlb_refill_handler
        nop

cache_error_entry:
        j cache_error_handler
        nop

exception_entry:
        j exception_handler
        nop     
        
exception_handler:
        KERNEL_STACK_TO_K0
        sub $k0, REGISTER_SPACE
        sw $sp, EOFFSET_SP($k0)
        move $sp, $k0
        
        mfc0 $k0, $cause
        
        sra $k0, $k0, 0x2               # cp0_exc_cause() part 1
        andi $k0, $k0, 0x1f             # cp0_exc_cause() part 2
        sub $k0, 8                      # 8 = SYSCALL
        
        beqz $k0, syscall_shortcut
        add $k0, 8                      # Revert $k0 back to correct exc number
        
        REGISTERS_STORE_AND_EXC_RESET $sp
        
        move $a1, $sp
        jal exc_dispatch                # exc_dispatch(excno, register_space)
        move $a0, $k0

        REGISTERS_LOAD $sp
        # The $sp is automatically restored to former value
        eret

## Syscall entry
#
# Registers:
#
# @param v0             Syscall number.
# @param a0             1st argument.
# @param a1             2nd argument.
# @param a2             3rd argument.
# @param a3             4th argument.
# @param t0             5th argument.
# @param t1             6th argument.
#
# @return               The return value will be stored in v0.
#
#define SS_SP           EOFFSET_SP
#define SS_STATUS       EOFFSET_STATUS
#define SS_EPC          EOFFSET_EPC
#define SS_K1           EOFFSET_K1
syscall_shortcut:
        # We have a lot of space on the stack, with free use
        mfc0 $t3, $epc
        mfc0 $t2, $status
        sw $t3, SS_EPC($sp)             # Save EPC
        sw $k1, SS_K1($sp)              # Save k1 not saved on context switch
        
        and $t4, $t2, REG_SAVE_MASK     # Save only KSU, EXL, ERL, IE
        li $t5, ~(0x1f)
        and $t2, $t2, $t5               # Clear KSU, EXL, ERL
        ori $t2, $t2, 0x1               # Set IE

        sw $t4, SS_STATUS($sp)
        mtc0 $t2, $status

        #
        # Call the higher level system call handler
        # We are going to reuse part of the unused exception stack frame
        #
        sw $t0, STACK_ARG4($sp)         # save the 5th argument on the stack
        sw $t1, STACK_ARG5($sp)         # save the 6th argument on the stack
        jal syscall_handler
        sw $v0, STACK_ARG6($sp)         # save the syscall number on the stack

        # restore status
        mfc0 $t2, $status
        lw $t3, SS_STATUS($sp)

        # Change back to EXL = 1 (from last exception), otherwise
        # an interrupt could rewrite the CP0 - EPC
        li $t4, ~REG_SAVE_MASK          # Mask UM, EXL, ERL, IE
        and $t2, $t2, $t4
        or $t2, $t2, $t3                # Copy saved UM, EXL, ERL, IE
        mtc0 $t2, $status
                        
        # restore epc + 4
        lw $t2, SS_EPC($sp)
        lw $k1, SS_K1($sp)
        addi $t2, $t2, 4
        mtc0 $t2, $epc
        
        lw $sp, SS_SP($sp)              # restore sp
        
        eret
                
tlb_refill_handler:
        KERNEL_STACK_TO_K0
        sub $k0, REGISTER_SPACE
        REGISTERS_STORE_AND_EXC_RESET $k0
        sw $sp,EOFFSET_SP($k0)
        add $sp, $k0, 0

        jal tlb_refill
        add $a0, $sp, 0 

        REGISTERS_LOAD $sp

        eret

cache_error_handler:
        KERNEL_STACK_TO_K0
        sub $k0, REGISTER_SPACE
        REGISTERS_STORE_AND_EXC_RESET $k0
        sw $sp,EOFFSET_SP($k0)
        add $sp, $k0, 0

        jal cache_error
        add $a0, $sp, 0 

        REGISTERS_LOAD $sp

        eret

userspace_asm:
        add $sp, $a0, 0
        add $v0, $a1, 0 
        add $t9, $a2, 0                 # Set up correct entry into PIC code
        xor $a0, $a0, $a0               # $a0 is defined to hold pcb_ptr
                                        # set it to 0
        eret