Spike

/* ------- */
void boot_loader(uintptr_t dtb):
  uintptr_t kernel_stack_top = pk_vm_init();
  extern char trap_entry;
  write_csr(stvec, pa2kva(&trap_entry));
  /* ... */

/* ------- */
trap_entry:
  csrrw sp, sscratch, sp
  bnez sp, 1f
  csrr sp, sscratch
1:addi sp,sp,-320
  save_tf
  move  a0,sp
  jal handle_trap

/* ------- */
void handle_trap(trapframe_t* tf):
  if ((intptr_t)tf->cause < 0)
    return handle_interrupt(tf);

  typedef void (*trap_handler)(trapframe_t*);

  const static trap_handler trap_handlers[] = {
    [CAUSE_MISALIGNED_FETCH] = handle_misaligned_fetch,
    [CAUSE_FETCH_ACCESS] = handle_instruction_access_fault,
    [CAUSE_LOAD_ACCESS] = handle_load_access_fault,
    [CAUSE_STORE_ACCESS] = handle_store_access_fault,
    [CAUSE_FETCH_PAGE_FAULT] = handle_fault_fetch,
    [CAUSE_ILLEGAL_INSTRUCTION] = handle_illegal_instruction,
    [CAUSE_USER_ECALL] = handle_syscall,
    /* ... */
  };
  trap_handler f = (void*)pa2kva(trap_handlers[tf->cause]);
  f(tf);

/* ------- */
static void handle_syscall(trapframe_t* tf):
  tf->gpr[10] = do_syscall(tf->gpr[10], tf->gpr[11], tf->gpr[12], tf->gpr[13],
                           tf->gpr[14], tf->gpr[15], tf->gpr[17]);
  tf->epc += 4;

/* ------- */
long do_syscall(long a0, long a1, long a2, long a3, long a4, long a5, unsigned long n):
  const static void* syscall_table[] = {
    [SYS_exit] = sys_exit,
    [SYS_exit_group] = sys_exit,
    [SYS_read] = sys_read,
    [SYS_pread] = sys_pread,
    [SYS_write] = sys_write,
    /* ... */
  };

  syscall_t f = 0;
  if (n < ARRAY_SIZE(syscall_table))
    f = syscall_table[n];
  if (!f)
    return sys_stub_nosys();
  f = (void*)pa2kva(f);
  return f(a0, a1, a2, a3, a4, a5, n);

/* ------- */
ssize_t sys_write(int fd, const char* buf, size_t n):
  /* ... */
  if (f):
    for (size_t total = 0;;):
      /* ... */
      r = file_write(f, kbuf, cur);
      /* ... */
    return r;


ssize_t file_write(file_t* f, const void* buf, size_t size):
  return frontend_syscall(SYS_write, f->kfd, kva2pa(buf), size, 0, 0, 0, 0);


long frontend_syscall(
    long n, uint64_t a0, uint64_t a1, uint64_t a2, uint64_t a3, uint64_t a4,
    uint64_t a5, uint64_t a6):
  static volatile uint64_t magic_mem[8];

  static spinlock_t lock = SPINLOCK_INIT;
  spinlock_lock(&lock);

  magic_mem[0] = n;
  magic_mem[1] = a0;
  magic_mem[2] = a1;
  magic_mem[3] = a2;
  magic_mem[4] = a3;
  magic_mem[5] = a4;
  magic_mem[6] = a5;
  magic_mem[7] = a6;

  htif_syscall(kva2pa_maybe(magic_mem));

  long ret = magic_mem[0];

  spinlock_unlock(&lock);
  return ret;

/* ------- */
void htif_syscall(uintptr_t arg):
  do_tohost_fromhost(0, 0, arg);

void sim_t::set_rom() {
    const int reset_vec_size = 8;

    reg_t start_pc = cfg->start_pc.value_or(get_entry_point());

    uint32_t reset_vec[reset_vec_size] = {
        // auipc  t0,0x0, 相当于 t0 = pc + (0x0<<12) = pc
        0x297,
        // 按约定 a1 需要保存 dtb 的地址. 这里的 dtb 是紧挨在 reset_vec 之后的:
        // rom.insert(rom.end(), dtb.begin(), dtb.end()).
        // reset_vec_size*4<<20 是因为 addi 指令里 imm 放在高 12 位
        0x28593 + (reset_vec_size * 4 << 20),          // addi   a1, t0, &dtb
        0xf1402573,                                    // csrr   a0, mhartid
        // 后面的 start_pc 所在的位置与 reset_vec 开头的位置 (t0) 相差 24 byte
        get_core(0)->get_xlen() == 32 ? 0x0182a283u :  // lw     t0,24(t0)
            0x0182b283u,                               // ld     t0,24(t0)
        0x28067,                                       // jr     t0
        // 这里插入一个 0, 是为了让 start_pc 与 reset_vec 开头的位置相差 24 byte
        // (而不是 20 byte), 以便 start_pc 的位置是 8 byte 对齐的 (ld 需要访问 8
        // byte 对齐的地址, reset_vec 的地址 DEFAULT_RSTVEC 已经是 8 byte 对齐的,
        // 再加上 24 得到的 start_pc 地址也会是对齐的)
        0,
        (uint32_t)(start_pc & 0xffffffff),
        (uint32_t)(start_pc >> 32)};
    // ...
    std::vector<char> rom(
        (char*)reset_vec, (char*)reset_vec + sizeof(reset_vec));

    rom.insert(rom.end(), dtb.begin(), dtb.end());
    const int align = 0x1000;
    rom.resize((rom.size() + align - 1) / align * align);

    boot_rom.reset(new rom_device_t(rom));
    bus.add_device(DEFAULT_RSTVEC, boot_rom.get());
}