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kernel.c
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//
// Created by ohye on 25. 1. 19.
//
#include "kernel.h"
typedef unsigned char uint8_t;
typedef unsigned int uint32_t;
typedef uint32_t size_t;
extern char __kernel_base[];
extern char __bss[], __bss_end[], __stack_top[];
extern char __free_ram[], __free_ram_end[];
extern char _binary_shell_bin_start[], _binary_shell_bin_size[];
struct sbiret sbi_call(long arg0, long arg1, long arg2, long arg3, long arg4, long arg5, long fid, long eid) {
register long a0 __asm__("a0") = arg0;
register long a1 __asm__("a1") = arg1;
register long a2 __asm__("a2") = arg2;
register long a3 __asm__("a3") = arg3;
register long a4 __asm__("a4") = arg4;
register long a5 __asm__("a5") = arg5;
register long a6 __asm__("a6") = fid;
register long a7 __asm__("a7") = eid;
__asm__ __volatile__("ecall"
: "=r"(a0), "=r"(a1)
: "r"(a0), "r"(a1), "r"(a2), "r"(a3), "r"(a4), "r"(a5), "r"(a6), "r"(a7)
: "memory");
return (struct sbiret){.error = a0, .value = a1};
}
void putchar(char ch) {
sbi_call(ch, 0, 0, 0, 0, 0, 0, 1);
}
long getchar(void) {
struct sbiret ret = sbi_call(0, 0, 0, 0, 0, 0, 0, 2);
return ret.error;
}
__attribute__((naked))
__attribute__((aligned(4)))
void kernel_entry(void) {
__asm__ __volatile__(
"csrrw sp, sscratch, sp\n" // 현재 스택포인터 값을 sscratch에 저장하고 sscratch에 저장된 커널스택 스택포인터 값을 가져온다.
"addi sp, sp, -4 * 31\n" // 현재 스택 포인터 -= 4 * 31 (32바이트 크기의 스택 확보)
"sw ra, 4 * 0(sp)\n" // 스택에 현재 레지스터 값 전부 저장
"sw gp, 4 * 1(sp)\n"
"sw tp, 4 * 2(sp)\n"
"sw t0, 4 * 3(sp)\n"
"sw t1, 4 * 4(sp)\n"
"sw t2, 4 * 5(sp)\n"
"sw t3, 4 * 6(sp)\n"
"sw t4, 4 * 7(sp)\n"
"sw t5, 4 * 8(sp)\n"
"sw t6, 4 * 9(sp)\n"
"sw a0, 4 * 10(sp)\n"
"sw a1, 4 * 11(sp)\n"
"sw a2, 4 * 12(sp)\n"
"sw a3, 4 * 13(sp)\n"
"sw a4, 4 * 14(sp)\n"
"sw a5, 4 * 15(sp)\n"
"sw a6, 4 * 16(sp)\n"
"sw a7, 4 * 17(sp)\n"
"sw s0, 4 * 18(sp)\n"
"sw s1, 4 * 19(sp)\n"
"sw s2, 4 * 20(sp)\n"
"sw s3, 4 * 21(sp)\n"
"sw s4, 4 * 22(sp)\n"
"sw s5, 4 * 23(sp)\n"
"sw s6, 4 * 24(sp)\n"
"sw s7, 4 * 25(sp)\n"
"sw s8, 4 * 26(sp)\n"
"sw s9, 4 * 27(sp)\n"
"sw s10, 4 * 28(sp)\n"
"sw s11, 4 * 29(sp)\n"
"csrr a0, sscratch\n" // 저장해둔 스택 포인터 값을 다시 불러와서 스택에 저장
"sw a0, 4 * 30(sp)\n"
"addi a0, sp, 4 * 31\n" // 커널 스택 값을 다시 복원해서 sscratch에 저장
"csrw sscratch, a0\n"
"mv a0, sp\n" // a0 레지스터에 현재 스택 포인터값을 넣어 handle_trap 호출 시 인자로 넘겨준다.
// handle_trap 함수는 struct trap frame* 타입의 인자를 하나 받는다.
// 스택에 값들을 넣고 난 다음의 스택 포인터 주소를 넘겨주어 struct trap frame*로 사용한다.
"call handle_trap\n" // handle_trap 함수 호출
"lw ra, 4 * 0(sp)\n" // 스택에 넣어두었던 값을 다시 레지스터로 가져온다.
"lw gp, 4 * 1(sp)\n"
"lw tp, 4 * 2(sp)\n"
"lw t0, 4 * 3(sp)\n"
"lw t1, 4 * 4(sp)\n"
"lw t2, 4 * 5(sp)\n"
"lw t3, 4 * 6(sp)\n"
"lw t4, 4 * 7(sp)\n"
"lw t5, 4 * 8(sp)\n"
"lw t6, 4 * 9(sp)\n"
"lw a0, 4 * 10(sp)\n"
"lw a1, 4 * 11(sp)\n"
"lw a2, 4 * 12(sp)\n"
"lw a3, 4 * 13(sp)\n"
"lw a4, 4 * 14(sp)\n"
"lw a5, 4 * 15(sp)\n"
"lw a6, 4 * 16(sp)\n"
"lw a7, 4 * 17(sp)\n"
"lw s0, 4 * 18(sp)\n"
"lw s1, 4 * 19(sp)\n"
"lw s2, 4 * 20(sp)\n"
"lw s3, 4 * 21(sp)\n"
"lw s4, 4 * 22(sp)\n"
"lw s5, 4 * 23(sp)\n"
"lw s6, 4 * 24(sp)\n"
"lw s7, 4 * 25(sp)\n"
"lw s8, 4 * 26(sp)\n"
"lw s9, 4 * 27(sp)\n"
"lw s10, 4 * 28(sp)\n"
"lw s11, 4 * 29(sp)\n"
"lw sp, 4 * 30(sp)\n"
"sret\n" // kernel_entry가 호출되었던 지점으로 복귀
);
}
paddr_t alloc_pages(uint32_t n) {
static paddr_t next_paddr = (paddr_t) __free_ram;
paddr_t curr_paddr = next_paddr;
next_paddr += (n * PAGE_SIZE);
if (next_paddr > (paddr_t) __free_ram_end) {
PANIC("out of memory: using %x, available: %x, tried to allocate %x.", \
curr_paddr, (paddr_t)__free_ram_end, next_paddr);
}
memset((void*) curr_paddr, 0, n * PAGE_SIZE);
return curr_paddr;
}
void map_page(uint32_t* table1, vaddr_t vaddr, paddr_t paddr, uint32_t flags) {
if (!is_aligned(vaddr, PAGE_SIZE))
PANIC("unaligned vaddr %x\n", vaddr);
if (!is_aligned(paddr, PAGE_SIZE))
PANIC("unaligned paddr %x\n", paddr);
uint32_t vpn1 = (vaddr >> 22) & 0x3FF;
if ((table1[vpn1] & PAGE_V) == 0) {
paddr_t table2_page_addr = alloc_pages(1);
table1[vpn1] = ((table2_page_addr / PAGE_SIZE) << 10) | PAGE_V;
}
uint32_t vpn2 = (vaddr >> 12) & 0x3FF;
paddr_t* table2 = (paddr_t*) ((table1[vpn1] >> 10) * PAGE_SIZE);
table2[vpn2] = ((paddr / PAGE_SIZE) << 10) | PAGE_V | flags;
}
__attribute__((naked))
void switch_context(uint32_t *prev_sp, uint32_t *next_sp) {
__asm__ __volatile__ (
"addi sp, sp, -4 * 13\n"
"sw ra , 0 * 4(sp)\n"
"sw s0 , 1 * 4(sp)\n"
"sw s1 , 2 * 4(sp)\n"
"sw s2 , 3 * 4(sp)\n"
"sw s3 , 4 * 4(sp)\n"
"sw s4 , 5 * 4(sp)\n"
"sw s5 , 6 * 4(sp)\n"
"sw s6 , 7 * 4(sp)\n"
"sw s7 , 8 * 4(sp)\n"
"sw s8 , 9 * 4(sp)\n"
"sw s9 , 10 * 4(sp)\n"
"sw s10, 11 * 4(sp)\n"
"sw s11, 12 * 4(sp)\n"
"sw sp, (a0)\n"
"lw sp, (a1)\n"
"lw ra , 0 * 4(sp)\n"
"lw s0 , 1 * 4(sp)\n"
"lw s1 , 2 * 4(sp)\n"
"lw s2 , 3 * 4(sp)\n"
"lw s3 , 4 * 4(sp)\n"
"lw s4 , 5 * 4(sp)\n"
"lw s5 , 6 * 4(sp)\n"
"lw s6 , 7 * 4(sp)\n"
"lw s7 , 8 * 4(sp)\n"
"lw s8 , 9 * 4(sp)\n"
"lw s9 , 10 * 4(sp)\n"
"lw s10, 11 * 4(sp)\n"
"lw s11, 12 * 4(sp)\n"
"addi sp, sp, 4 * 13\n"
"ret"
);
}
__attribute__((naked))
void user_entry(void) {
__asm__ __volatile__(
"csrw sepc, %[sepc] \n"
"csrw sstatus, %[sstatus] \n"
"sret"
:
: [sepc] "r" (USER_BASE),
[sstatus] "r" (SSTATUS_SPIE)
);
}
struct process procs[PROCS_MAX];
struct process* create_process(const void *image, size_t image_size) {
uint8_t i;
struct process* proc = NULL;
for (i = 0; i < PROCS_MAX; i++) {
if (procs[i].state == PROC_UNUSED) {
proc = &procs[i];
break;
}
}
if (proc == NULL) PANIC("There is no unused process slot.");
uint32_t *sp = (uint32_t*) &proc->stack[sizeof(proc->stack)];
*--sp = 0; // s11;
*--sp = 0; // s10;
*--sp = 0; // s9;
*--sp = 0; // s8;
*--sp = 0; // s7;
*--sp = 0; // s6;
*--sp = 0; // s5;
*--sp = 0; // s4;
*--sp = 0; // s3;
*--sp = 0; // s2;
*--sp = 0; // s1;
*--sp = 0; // s0;
*--sp = (uint32_t) user_entry; // ra;
paddr_t page_table = alloc_pages(1);
for (
paddr_t addr = (paddr_t)__kernel_base;
addr < (paddr_t)__free_ram_end;
addr += PAGE_SIZE
) {
map_page(
(uint32_t *)page_table,
addr,
addr,
PAGE_R | PAGE_W | PAGE_X
);
}
for (uint32_t offset = 0; offset < image_size; offset += PAGE_SIZE) {
paddr_t page = alloc_pages(1);
size_t remaining = image_size - offset;
size_t copy_size = PAGE_SIZE <= remaining ? PAGE_SIZE : remaining;
memcpy((void *)page, image + offset, copy_size);
map_page(
(uint32_t *)page_table,
USER_BASE + offset,
page,
PAGE_U | PAGE_R | PAGE_W | PAGE_X
);
}
proc->pid = i;
proc->state = PROC_RUNNABLE;
proc->sp = (uint32_t) sp;
proc->page_table = page_table;
return proc;
}
struct process *current_proc;
struct process *idle_proc;
void yield() {
struct process *next_proc = idle_proc;
for (int i = 1; i <= PROCS_MAX; i++) {
struct process *proc = &procs[(current_proc->pid + i) % PROCS_MAX];
if (proc->state == PROC_RUNNABLE && proc->pid > 0) {
next_proc = proc;
break;
}
}
if (next_proc == current_proc) return;
__asm__ __volatile__ ("sfence.vma");
WRITE_CSR(satp, (SATP_SV32 | ((uint32_t) next_proc->page_table / PAGE_SIZE)));
__asm__ __volatile__ ("sfence.vma");
WRITE_CSR(sscratch, (uint32_t) &next_proc->stack[sizeof(next_proc->stack)]);
struct process* prev_proc = current_proc;
current_proc = next_proc;
switch_context(&prev_proc->sp, &next_proc->sp);
}
void handle_syscall(struct trap_frame* f) {
switch (f->a3) {
case SYS_PUTCHAR:
putchar(f->a0);
break;
case SYS_GETCHAR:
while(1) {
long ch = getchar();
if (ch >= 0) {
f->a0 = ch;
break;
}
yield();
}
break;
case SYS_EXIT:
printf("process %d exited\n", current_proc->pid);
current_proc->state = PROC_EXITED;
yield();
PANIC("unreachable");
break;
default:
PANIC("unexpected syscall a3=%x\n", f->a3);
}
}
void handle_trap(struct trap_frame* f) {
uint32_t scause = READ_CSR(scause);
uint32_t stval = READ_CSR(stval);
uint32_t user_pc = READ_CSR(sepc);
if (scause == SCAUE_ECALL) {
handle_syscall(f);
user_pc += 4;
} else {
PANIC("unexpected trap scause=%x, stval=%x, sepc=%x\n", scause, stval, user_pc);
}
WRITE_CSR(sepc, user_pc);
}
void kernel_main(void) {
memset(__bss, 0, (size_t) __bss_end - (size_t) __bss);
WRITE_CSR(stvec, (uint32_t) kernel_entry);
idle_proc = create_process(NULL, 0);
idle_proc->pid = -1;
current_proc = idle_proc;
create_process(_binary_shell_bin_start, (size_t) _binary_shell_bin_size);
yield();
PANIC("switched to idle process");
}
__attribute__((section(".text.boot")))
__attribute__((naked))
void boot(void) {
__asm__ __volatile__(
"mv sp, %[stack_top]\n" // Set the stack pointer
"j kernel_main\n" // Jump to the kernel main function
:
: [stack_top] "r" (__stack_top) // Pass the stack top address as %[stack_top]
);
}