update name of code to labcodes

2013-09-17 22:21:48 +08:00
parent 759eca9dda
commit 3f8d5876b9
726 changed files with 0 additions and 0 deletions
--- a/labcodes/lab8/boot/bootmain.c
+++ b/labcodes/lab8/boot/bootmain.c
@@ -0,0 +1,116 @@
+#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);
+}
+