117 lines
3.2 KiB
C
117 lines
3.2 KiB
C
#include <defs.h>
|
|
#include <x86.h>
|
|
#include <elf.h>
|
|
|
|
/* *********************************************************************
|
|
* This a dirt simple boot loader, whose sole job is to boot
|
|
* an ELF kernel image from the first IDE hard disk.
|
|
*
|
|
* DISK LAYOUT
|
|
* * This program(bootasm.S and bootmain.c) is the bootloader.
|
|
* It should be stored in the first sector of the disk.
|
|
*
|
|
* * The 2nd sector onward holds the kernel image.
|
|
*
|
|
* * The kernel image must be in ELF format.
|
|
*
|
|
* BOOT UP STEPS
|
|
* * when the CPU boots it loads the BIOS into memory and executes it
|
|
*
|
|
* * the BIOS intializes devices, sets of the interrupt routines, and
|
|
* reads the first sector of the boot device(e.g., hard-drive)
|
|
* into memory and jumps to it.
|
|
*
|
|
* * Assuming this boot loader is stored in the first sector of the
|
|
* hard-drive, this code takes over...
|
|
*
|
|
* * control starts in bootasm.S -- which sets up protected mode,
|
|
* and a stack so C code then run, then calls bootmain()
|
|
*
|
|
* * bootmain() in this file takes over, reads in the kernel and jumps to it.
|
|
* */
|
|
|
|
#define SECTSIZE 512
|
|
#define ELFHDR ((struct elfhdr *)0x10000) // scratch space
|
|
|
|
/* waitdisk - wait for disk ready */
|
|
static void
|
|
waitdisk(void) {
|
|
while ((inb(0x1F7) & 0xC0) != 0x40)
|
|
/* do nothing */;
|
|
}
|
|
|
|
/* readsect - read a single sector at @secno into @dst */
|
|
static void
|
|
readsect(void *dst, uint32_t secno) {
|
|
// wait for disk to be ready
|
|
waitdisk();
|
|
|
|
outb(0x1F2, 1); // count = 1
|
|
outb(0x1F3, secno & 0xFF);
|
|
outb(0x1F4, (secno >> 8) & 0xFF);
|
|
outb(0x1F5, (secno >> 16) & 0xFF);
|
|
outb(0x1F6, ((secno >> 24) & 0xF) | 0xE0);
|
|
outb(0x1F7, 0x20); // cmd 0x20 - read sectors
|
|
|
|
// wait for disk to be ready
|
|
waitdisk();
|
|
|
|
// read a sector
|
|
insl(0x1F0, dst, SECTSIZE / 4);
|
|
}
|
|
|
|
/* *
|
|
* readseg - read @count bytes at @offset from kernel into virtual address @va,
|
|
* might copy more than asked.
|
|
* */
|
|
static void
|
|
readseg(uintptr_t va, uint32_t count, uint32_t offset) {
|
|
uintptr_t end_va = va + count;
|
|
|
|
// round down to sector boundary
|
|
va -= offset % SECTSIZE;
|
|
|
|
// translate from bytes to sectors; kernel starts at sector 1
|
|
uint32_t secno = (offset / SECTSIZE) + 1;
|
|
|
|
// If this is too slow, we could read lots of sectors at a time.
|
|
// We'd write more to memory than asked, but it doesn't matter --
|
|
// we load in increasing order.
|
|
for (; va < end_va; va += SECTSIZE, secno ++) {
|
|
readsect((void *)va, secno);
|
|
}
|
|
}
|
|
|
|
/* bootmain - the entry of bootloader */
|
|
void
|
|
bootmain(void) {
|
|
// read the 1st page off disk
|
|
readseg((uintptr_t)ELFHDR, SECTSIZE * 8, 0);
|
|
|
|
// is this a valid ELF?
|
|
if (ELFHDR->e_magic != ELF_MAGIC) {
|
|
goto bad;
|
|
}
|
|
|
|
struct proghdr *ph, *eph;
|
|
|
|
// load each program segment (ignores ph flags)
|
|
ph = (struct proghdr *)((uintptr_t)ELFHDR + ELFHDR->e_phoff);
|
|
eph = ph + ELFHDR->e_phnum;
|
|
for (; ph < eph; ph ++) {
|
|
readseg(ph->p_va & 0xFFFFFF, ph->p_memsz, ph->p_offset);
|
|
}
|
|
|
|
// call the entry point from the ELF header
|
|
// note: does not return
|
|
((void (*)(void))(ELFHDR->e_entry & 0xFFFFFF))();
|
|
|
|
bad:
|
|
outw(0x8A00, 0x8A00);
|
|
outw(0x8A00, 0x8E00);
|
|
|
|
/* do nothing */
|
|
while (1);
|
|
}
|
|
|