101 lines
2.8 KiB
C
101 lines
2.8 KiB
C
// Boot loader.
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//
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// Part of the boot block, along with mbr.S, which calls bootmain().
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// mbr.S has put the processor into protected 32-bit mode.
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// bootmain() loads an ELF kernel image from the disk starting at
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// sector 3 and then jumps to the kernel entry routine.
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#include "drivers/port.h"
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#include "elf.h"
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#define SECTSIZE 512
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typedef unsigned char uchar;
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typedef unsigned int uint;
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void readseg(uchar *, uint, uint);
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inline void stosb(uchar *addr, uchar byte, uint count) {
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asm volatile("cld; rep stosb" : "+D"(addr), "+a"(byte) : "c"(count) : "cc");
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}
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void bootmain(void) {
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Elf32_Ehdr *elf;
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Elf32_Phdr *ph, *eph;
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void (*entry)(void);
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uchar *pa;
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elf = (Elf32_Ehdr *)0x30000; // scratch space
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// Read 1st page off disk
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readseg((uchar *)elf, 4096, 0);
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// Is this an ELF executable?
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if (elf->magic != ELF_MAGIC)
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return; // let bootasm.S handle error
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// Load each program segment (ignores ph flags).
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ph = (Elf32_Phdr *)((uchar *)elf + elf->e_phoff);
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eph = ph + elf->e_phnum;
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for (; ph < eph; ph++) {
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pa = (uchar *)(ph->p_paddr & 0x0fffffff);
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readseg(pa, ph->p_filesz, ph->p_offset);
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if (ph->p_memsz > ph->p_filesz)
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stosb(pa + ph->p_filesz, 0, ph->p_memsz - ph->p_filesz);
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}
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// Call the entry point from the ELF header.
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// Does not return!
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entry = (void (*)(void))(elf->e_entry & 0x0fffffff);
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entry();
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}
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void waitdisk(void) {
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// Wait for disk ready.
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while ((port_byte_in(0x1F7) & 0xC0) != 0x40)
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;
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}
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static inline void insl(int port, void *addr, int cnt) {
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asm volatile("cld; rep insl"
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: "=D"(addr), "=c"(cnt)
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: "d"(port), "0"(addr), "1"(cnt)
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: "memory", "cc");
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}
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// Read a single sector at offset into dst.
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void readsect(void *dst, uint offset) {
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// Issue command.
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waitdisk();
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port_byte_out(0x1F2, 1); // count = 1
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port_byte_out(0x1F3, offset);
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port_byte_out(0x1F4, offset >> 8);
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port_byte_out(0x1F5, offset >> 16);
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port_byte_out(0x1F6, (offset >> 24) | 0xE0);
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port_byte_out(0x1F7, 0x20); // cmd 0x20 - read sectors
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// Read data.
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waitdisk();
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insl(0x1F0, dst, SECTSIZE / 4);
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}
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// Read 'count' bytes at 'offset' from kernel into physical address 'pa'.
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// Might copy more than asked.
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void readseg(uchar *pa, uint count, uint offset) {
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uchar *epa;
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epa = pa + count;
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// Round down to sector boundary.
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pa -= offset % SECTSIZE;
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// Translate from bytes to sectors; kernel starts at sector 3.
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offset = (offset / SECTSIZE) + 2;
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// If this is too slow, we could read lots of sectors at a time.
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// We'd write more to memory than asked, but it doesn't matter --
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// we load in increasing order.
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for (; pa < epa; pa += SECTSIZE, offset++)
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readsect(pa, offset);
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}
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