minisel.c

// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// This file is a barebones, minimal-dependency rootserver (root app) for seL4
// that uses no standard C libraries or startfiles. It prints bootinfo to the
// console using the seL4_DebugPutChar syscall and is intended as a starting
// point for low-level seL4 tests.

#include <stdint.h>
#include <stdarg.h>

#include <sel4/bootinfo.h>
#include <sel4/arch/syscalls.h>

seL4_BootInfo *bootinfo;
__thread seL4_IPCBuffer *__sel4_ipc_buffer;

char minisel_stack[16384] __attribute__((__aligned__(4096)));
char minisel_tls[4096] __attribute__((__aligned__(4096)));

__attribute__((naked)) void _start() {
  asm volatile(
    ".option push                  \n"
    ".option norelax               \n"
    "la gp, __global_pointer$      \n"
    "la sp, minisel_stack + 4096   \n"
    "la x4, minisel_tls            \n"
    "la t0, bootinfo               \n"
    "sw a0, 0(t0)                  \n"
    ".option pop                   \n"
    "j main                        \n"
  );
}

// only prints 32-bit "%x" hex values
void minisel_printf(const char *fmt, ...) {
  va_list args;
  va_start(args, fmt);
  for (; *fmt; fmt++) {
    if (*fmt == '%') {
      fmt++;
      if (*fmt == 'x') {
        uint32_t arg = va_arg(args, uint32_t);
        for (int i = 7; i >= 0; i--) {
          int n = (arg >> (4 * i)) & 0xF;
          seL4_DebugPutChar(n > 9 ? 'A' + n - 10 : '0' + n);
        }
      }
    } else {
      seL4_DebugPutChar(*fmt);
    }
  }
  va_end(args);
}

int main(void) {
  minisel_printf("\n");
  minisel_printf("########################################\n");
  minisel_printf("Minisel startup, bootinfo @ %x\n", bootinfo);
  minisel_printf("extraLen %x\n", bootinfo->extraLen);
  minisel_printf("nodeID %x\n", bootinfo->nodeID);
  minisel_printf("numNodes %x\n", bootinfo->numNodes);
  minisel_printf("numIOPTLevels %x\n", bootinfo->numIOPTLevels);
  minisel_printf("ipcBuffer %x\n", bootinfo->ipcBuffer);
  minisel_printf("initThreadCNodeSizeBits %x\n", bootinfo->initThreadCNodeSizeBits);
  minisel_printf("CONFIG_MAX_NUM_BOOTINFO_UNTYPED_CAPS %x\n", CONFIG_MAX_NUM_BOOTINFO_UNTYPED_CAPS);
  minisel_printf("\n");

  int slot_a = bootinfo->untyped.start;
  int slot_b = bootinfo->untyped.end;

  minisel_printf("slot_a %x\n", slot_a);
  minisel_printf("slot_b %x\n", slot_b);
  minisel_printf("\n");

  for (int i = 0; i < (slot_b - slot_a); i++) {
    seL4_UntypedDesc u = bootinfo->untypedList[i];
    uint32_t paddr_a = u.paddr;
    uint32_t paddr_b = paddr_a + (1 << u.sizeBits);
    minisel_printf("paddr %x:%x isDevice %x\n", paddr_a, paddr_b, u.isDevice);
  }
  minisel_printf("\n");

  minisel_printf("Done, sleeping in WFI loop\n");
  while(1) {
    asm("wfi");
  }
}