b7f653dc49
do Bochs breakpoint and spin in bootasm.S. not needed in bootmain too. fix readseg bug (rounding of va). zero segments when memsz > filesz. no need to clear BSS in kernel main. make bootother.S like bootasm.S
96 lines
2.2 KiB
C
96 lines
2.2 KiB
C
// Boot loader.
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//
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// Part of the boot sector, along with bootasm.S, which calls bootmain().
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// bootasm.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 1 and then jumps to the kernel entry routine.
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#include "types.h"
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#include "elf.h"
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#include "x86.h"
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#define SECTSIZE 512
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void readseg(uchar*, uint, uint);
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void
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bootmain(void)
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{
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struct elfhdr *elf;
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struct proghdr *ph, *eph;
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void (*entry)(void);
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uchar* va;
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elf = (struct elfhdr*)0x10000; // 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 = (struct proghdr*)((uchar*)elf + elf->phoff);
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eph = ph + elf->phnum;
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for(; ph < eph; ph++) {
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va = (uchar*)(ph->va & 0xFFFFFF);
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readseg(va, ph->filesz, ph->offset);
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if(ph->memsz > ph->filesz)
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stosb(va + ph->filesz, 0, ph->memsz - ph->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->entry & 0xFFFFFF);
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entry();
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}
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void
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waitdisk(void)
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{
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// Wait for disk ready.
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while((inb(0x1F7) & 0xC0) != 0x40)
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;
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}
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// Read a single sector at offset into dst.
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void
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readsect(void *dst, uint offset)
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{
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// Issue command.
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waitdisk();
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outb(0x1F2, 1); // count = 1
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outb(0x1F3, offset);
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outb(0x1F4, offset >> 8);
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outb(0x1F5, offset >> 16);
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outb(0x1F6, (offset >> 24) | 0xE0);
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outb(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 virtual address 'va'.
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// Might copy more than asked.
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void
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readseg(uchar* va, uint count, uint offset)
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{
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uchar* eva;
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eva = va + count;
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// Round down to sector boundary.
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va -= offset % SECTSIZE;
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// Translate from bytes to sectors; kernel starts at sector 1.
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offset = (offset / SECTSIZE) + 1;
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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(; va < eva; va += SECTSIZE, offset++)
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readsect(va, offset);
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}
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