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Initial Spring 2016 commit.

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Geoffrey Challen
2015-12-23 00:50:04 +00:00
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/*
* Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
* The President and Fellows of Harvard College.
*
* 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 University 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 UNIVERSITY 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 UNIVERSITY 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.
*/
#include <kern/mips/regdefs.h>
#include <mips/specialreg.h>
.set noreorder
.text
.globl __start
.type __start,@function
.ent __start
__start:
/*
* Stack frame. We save the return address register, even though
* it contains nothing useful. This is for gdb's benefit when it
* comes disassembling. We also need 16 bytes for making a call,
* and we have to align to an 8-byte (64-bit) boundary, so the
* total frame size is 24.
*
* Note that the frame here must match the frame we set up below
* when we switch off the bootup stack. Otherwise, gdb gets very
* confused.
*/
.frame sp, 24, $0 /* 24-byte sp-relative frame; return addr on stack */
.mask 0x80000000, -4 /* register 31 (ra) saved at (sp+24)-4 */
addiu sp, sp, -24
sw ra, 20(sp)
/*
* The System/161 loader sets up a boot stack for the first
* processor at the top of physical memory, and passes us a single
* string argument. The string lives on the very top of the stack.
* We get its address in a0.
*
* The kernel loads at virtual address 0x80000200, which is
* physical address 0x00000200. The space immediately below this
* is reserved for the exception vector code.
*
* The symbol _end is generated by the linker. It's the address of
* the end of the kernel. It's not a variable; the *value* of the
* _end symbol itself is this address. In C you'd use "&_end".
*
* We set up the memory map like this:
*
* top of memory
* free memory
* P + 0x1000
* first thread's stack (1 page)
* P
* wasted space (< 1 page)
* copy of the boot string
* _end
* kernel
* 0x80000200
* exception handlers
* 0x80000000
*
* where P is the next whole page after copying the argument string.
*/
la s0, _end /* stash _end in a saved register */
move a1, a0 /* move bootstring to the second argument */
move a0, s0 /* make _end the first argument */
jal strcpy /* call strcpy(_end, bootstring) */
nop /* delay slot */
move a0, s0 /* make _end the first argument again */
jal strlen /* call strlen(_end) */
nop
add t0, s0, v0 /* add in the length of the string */
addi t0, t0, 1 /* and the null terminator */
addi t0, t0, 4095 /* round up to next page boundary */
li t1, 0xfffff000
and t0, t0, t1
addi t0, t0, 4096 /* add one page to hold the stack */
move sp, t0 /* start the kernel stack for the first thread here */
sw t0, firstfree /* remember the first free page for later */
/*
* At this point, s0 contains the boot argument string, and no other
* registers contain anything interesting (except the stack pointer).
*/
/*
* Now set up a stack frame on the real kernel stack: a dummy saved
* return address and four argument slots for making function calls,
* plus a wasted slot for alignment.
*
* (This needs to match the stack frame set up at the top of the
* function, or the debugger gets confused.)
*/
addiu sp, sp, -24
sw $0, 20(sp)
/*
* Now, copy the exception handler code onto the first page of memory.
*/
li a0, EXADDR_UTLB
la a1, mips_utlb_handler
la a2, mips_utlb_end
sub a2, a2, a1
jal memmove
nop
li a0, EXADDR_GENERAL
la a1, mips_general_handler
la a2, mips_general_end
sub a2, a2, a1
jal memmove
nop
/*
* Flush the instruction cache to make sure the above changes show
* through to instruction fetch.
*/
jal mips_flushicache
nop
/*
* Initialize the TLB.
*/
jal tlb_reset
nop
/*
* Load NULL into the register we use for curthread.
*/
li s7, 0
/*
* Set up the status register.
*
* The MIPS has six hardware interrupt lines and two software interrupts.
* These are individually maskable in the status register. However, we
* don't use this feature (for simplicity) - we only use the master
* interrupt enable/disable flag in bit 0. So enable all of those bits
* now and forget about them.
*
* The BEV bit in the status register, if set, causes the processor to
* jump to a different set of hardwired exception handling addresses.
* This is so that the kernel's exception handling code can be loaded
* into RAM and that the boot ROM's exception handling code can be ROM.
* This flag is normally set at boot time, and we need to be sure to
* clear it.
*
* The KUo/IEo/KUp/IEp/KUc/IEc bits should all start at zero.
*
* We also want all the other random control bits (mostly for cache
* stuff) set to zero.
*
* Thus, the actual value we write is CST_IRQMASK.
*/
li t0, CST_IRQMASK /* get value */
mtc0 t0, c0_status /* set status register */
/*
* Load the CPU number into the PTBASE field of the CONTEXT
* register. This is necessary to read from cpustacks[] and
* cputhreads[] on trap entry from user mode. See further
* discussions elsewhere.
*
* Because the boot CPU is CPU 0, we can just send 0.
*/
mtc0 $0, c0_context
/*
* Load the GP register. This is a MIPS ABI feature; the GP
* register points to an address in the middle of the data segment,
* so data can be accessed relative to GP using one instruction
* instead of the two it takes to set up a full 32-bit address.
*/
la gp, _gp
/*
* We're all set up!
* Fetch the copy of the bootstring as the argument, and call main.
*/
jal kmain
move a0, s0 /* in delay slot */
/*
* kmain shouldn't return. panic.
* Loop back just in case panic returns too.
*/
1:
la a0, panicstr
jal panic
nop /* delay slot */
j 1b
nop /* delay slot */
.end __start
.rdata
panicstr:
.asciz "kmain returned\n"
/*
* CPUs started after the boot CPU come here.
*/
.text
.globl cpu_start_secondary
.type cpu_start_secondary,@function
.ent cpu_start_secondary
cpu_start_secondary:
/*
* When we get here our stack points to the CRAM area of the bus
* controller per-CPU space. This means we can, with a bit of
* caution, call C functions, but nothing very deeply nesting.
* However, we don't need to.
*
* The a0 register contains the value that was put in the second
* word of the CRAM area, which is the (software) cpu number for
* indexing cpustacks[]. None of the other registers contain
* anything useful.
*/
/*
* Stack frame. We save the return address register, even though
* it contains nothing useful. This is for gdb's benefit when it
* comes disassembling. We also need 16 bytes for making a call,
* and 4 bytes for alignment, so the total frame size is 24.
*
* Note that the frame here must match the frame we set up below
* when we switch stacks. Otherwise, gdb gets very confused.
*/
.frame sp, 24, $0 /* 24-byte sp-relative frame; return addr on stack */
.mask 0x80000000, -4 /* register 31 (ra) saved at (sp+24)-4 */
addiu sp, sp, -24
sw ra, 20(sp)
/*
* Fetch the stack out of cpustacks[].
*/
lui t0, %hi(cpustacks) /* load upper half of cpustacks base addr */
sll v0, a0, 2 /* get byte index for array (multiply by 4) */
addu t0, t0, v0 /* add it in */
lw sp, %lo(cpustacks)(t0) /* get the stack pointer */
/*
* Now fetch curthread out of cputhreads[].
*/
lui t0, %hi(cputhreads) /* load upper half of cpustacks base addr */
sll v0, a0, 2 /* get byte index for array (multiply by 4) */
addu t0, t0, v0 /* add it in */
lw s7, %lo(cputhreads)(t0) /* load curthread register */
/*
* Initialize the TLB.
*/
jal tlb_reset
nop
/*
* Set up the status register, as described above.
*/
li t0, CST_IRQMASK /* get value */
mtc0 t0, c0_status /* set status register */
/*
* Load the CPU number into the PTBASE field of the CONTEXT
* register, as described above.
*/
sll v0, a0, CTX_PTBASESHIFT
mtc0 v0, c0_context
/*
* Initialize the on-chip timer interrupt.
*
* This should be set to CPU_FREQUENCY/HZ, but we don't have either
* of those values here, so we'll arbitrarily set it to 100,000. It
* will get reset to the right thing after it first fires.
*/
li v0, 100000
mtc0 v0, c0_compare
/*
* Load the GP register.
*/
la gp, _gp
/*
* Set up a stack frame. Store zero into the return address slot so
* we show as the top of the stack.
*/
addiu sp, sp, -24
sw z0, 20(sp)
/*
* Off to MI code. Pass the cpu number as the argument; it's already
* in the a0 register.
*/
j cpu_hatch
nop /* delay slot for jump */
.end cpu_start_secondary