1// Boot loader.
2//
3// Part of the boot block, along with bootasm.S, which calls bootmain().
4// bootasm.S has put the processor into protected 32-bit mode.
5// bootmain() loads an ELF kernel image from the disk starting at
6// sector 1 and then jumps to the kernel entry routine.
7
8#include "types.h"
9#include "elf.h"
10#include "x86.h"
11#include "memlayout.h"
12
13#define SECTSIZE 512
14
15void readseg(uchar*, uint, uint);
16
17void
18bootmain(void)
19{
20 struct elfhdr *elf;
21 struct proghdr *ph, *eph;
22 void (*entry)(void);
23 uchar* pa;
24
25 elf = (struct elfhdr*)0x10000; // scratch space
26
27 // Read 1st page off disk
28 readseg((uchar*)elf, 4096, 0);
29
30 // Is this an ELF executable?
31 if(elf->magic != ELF_MAGIC)
32 return; // let bootasm.S handle error
33
34 // Load each program segment (ignores ph flags).
35 ph = (struct proghdr*)((uchar*)elf + elf->phoff);
36 eph = ph + elf->phnum;
37 for(; ph < eph; ph++){
38 pa = (uchar*)ph->paddr;
39 readseg(pa, ph->filesz, ph->off);
40 if(ph->memsz > ph->filesz)
41 stosb(pa + ph->filesz, 0, ph->memsz - ph->filesz);
42 }
43
44 // Call the entry point from the ELF header.
45 // Does not return!
46 entry = (void(*)(void))(elf->entry);
47 entry();
48}
49
50void
51waitdisk(void)
52{
53 // Wait for disk ready.
54 while((inb(0x1F7) & 0xC0) != 0x40)
55 ;
56}
57
58// Read a single sector at offset into dst.
59void
60readsect(void *dst, uint offset)
61{
62 // Issue command.
63 waitdisk();
64 outb(0x1F2, 1); // count = 1
65 outb(0x1F3, offset);
66 outb(0x1F4, offset >> 8);
67 outb(0x1F5, offset >> 16);
68 outb(0x1F6, (offset >> 24) | 0xE0);
69 outb(0x1F7, 0x20); // cmd 0x20 - read sectors
70
71 // Read data.
72 waitdisk();
73 insl(0x1F0, dst, SECTSIZE/4);
74}
75
76// Read 'count' bytes at 'offset' from kernel into physical address 'pa'.
77// Might copy more than asked.
78void
79readseg(uchar* pa, uint count, uint offset)
80{
81 uchar* epa;
82
83 epa = pa + count;
84
85 // Round down to sector boundary.
86 pa -= offset % SECTSIZE;
87
88 // Translate from bytes to sectors; kernel starts at sector 1.
89 offset = (offset / SECTSIZE) + 1;
90
91 // If this is too slow, we could read lots of sectors at a time.
92 // We'd write more to memory than asked, but it doesn't matter --
93 // we load in increasing order.
94 for(; pa < epa; pa += SECTSIZE, offset++)
95 readsect(pa, offset);
96}
97