#include <stdio.h>

#include <string.h>

#include "bootstrap.h"

// This must match bootsector.map

#define SECTORS_TO_COPY 0x40

#define DST_SEGMENT 0x42

#define INITIAL_IP 0x44

#define INITIAL_SP 0x46

#define INITIAL_CS 0x48

#define INITIAL_DS 0x4A

#define INITIAL_SS 0x4C

#define BYTES_PER_SECTOR 0x0B

#define SECTORS_PER_CLUSTER 0x0D

#define RESERVED_SECTORS 0x0E

#define N_FATS 0x10

#define MAX_ROOT_DIR_ENTRIES 0x11

#define TOTAL_LOGICAL_SECTORS 0x13

#define MEDIA_DESCRIPTOR 0x15

#define LOGICAL_SECTORS_PER_FAT 0x16

#define SECTORS_PER_TRACK 0x18

#define NUM_HEADS 0x1A

#define NUM_HIDDEN_SECTORS 0x1C

static unsigned char bootstrap_buf[513];

#define SET_16LE(off, val) do { bootstrap_buf[off] = val; bootstrap_buf[off+1] = val >> 8; } while(0)

#define SET_32LE(off, val) do { bootstrap_buf[off] = val; bootstrap_buf[off+1] = val >> 8; bootstrap_buf[off+2] = val >> 16; bootstrap_buf[off+3] = val >> 24; } while(0)

int bootstrap_write(unsigned short num_sectors_to_copy,

unsigned short dst_segment,

unsigned short initial_ip,

unsigned short initial_sp,

unsigned short initial_cs,

unsigned short initial_ds,

unsigned short initial_ss,

struct bootstrap_bpb *bpb,

const char *label,

FILE *out_fptr)

{

char label_buf[12];

int label_len;

memset(label_buf, ' ', sizeof(label_buf));

label_len = strlen(label);

if (label_len > 11) {

fprintf(stderr, "Disk label '%s' is too long (max 11 chars.).\n", label);

return -1;

}

SET_16LE(DST_SEGMENT, dst_segment);

bootstrap_buf[SECTORS_TO_COPY] = num_sectors_to_copy & 0xff;

bootstrap_buf[SECTORS_TO_COPY+1] = num_sectors_to_copy >> 8;

if (bpb) {

SET_16LE(BYTES_PER_SECTOR, bpb->bytes_per_logical_sector);

bootstrap_buf[SECTORS_PER_CLUSTER] = bpb->sectors_per_cluster;

SET_16LE(RESERVED_SECTORS, bpb->reserved_logical_sectors);

bootstrap_buf[N_FATS] = bpb->n_fats;

SET_16LE(MAX_ROOT_DIR_ENTRIES, bpb->root_dir_entries);

SET_16LE(TOTAL_LOGICAL_SECTORS, bpb->total_logical_sectors);

bootstrap_buf[MEDIA_DESCRIPTOR] = bpb->media_descriptor;

SET_16LE(LOGICAL_SECTORS_PER_FAT, bpb->logical_sectors_per_fat);

bootstrap_buf[SECTORS_PER_TRACK] = bpb->sectors_per_track;

SET_16LE(NUM_HEADS, bpb->num_heads);

SET_32LE(NUM_HIDDEN_SECTORS, 0);

bootstrap_buf[0x26] = 0x29; // EBPB signature

memcpy(bootstrap_buf + 0x2b, label_buf, sizeof(label_buf));

memcpy(bootstrap_buf + 0x36, "FAT12 ", 8);

}

bootstrap_buf[INITIAL_IP] = initial_ip & 0xff;

bootstrap_buf[INITIAL_IP+1] = initial_ip >> 8;

bootstrap_buf[INITIAL_SP] = initial_sp & 0xff;

bootstrap_buf[INITIAL_SP+1] = initial_sp >> 8;

bootstrap_buf[INITIAL_CS] = initial_cs & 0xff;

bootstrap_buf[INITIAL_CS+1] = initial_cs >> 8;

bootstrap_buf[INITIAL_DS] = initial_ds & 0xff;

bootstrap_buf[INITIAL_DS+1] = initial_ds >> 8;

bootstrap_buf[INITIAL_SS] = initial_ss & 0xff;

bootstrap_buf[INITIAL_SS+1] = initial_ss >> 8;

return fwrite(bootstrap_buf, 512, 1, out_fptr);

}

int bootstrap_load(const char *filename)

{

FILE *fptr_bootstrap;

int bootstrap_size;

fptr_bootstrap = fopen(filename, "rb");

if (!fptr_bootstrap) {

perror("could not open bootstrap");

return -1;

}

memset(bootstrap_buf, 0, sizeof(bootstrap_buf));

bootstrap_size = fread(bootstrap_buf, 1, 513, fptr_bootstrap);

if (bootstrap_size < 0) {

perror("fread");

fclose(fptr_bootstrap);

return -1;

}

if (bootstrap_size > 512) {

fprintf(stderr, "Bootstrap too large");

fclose(fptr_bootstrap);

return -1;

}

fclose(fptr_bootstrap);

return bootstrap_size;

}