rdos/host/sys.c

203 lines
5.0 KiB
C
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#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#define min(a, b) (((a) < (b)) ? (a) : (b))
// argv[1] must be floppy image
// argv[2] must be name of boot com
// if you expect to see memory safety, close your editor NOW!
#define AH 4
#define AX 0
#define CX 1
#define DH 6
#define BX 3
#define SP 4
#define SI 6
#define DI 7
char* push_imm8(char* addr, int i) {
*(int8_t*)addr = i;
return(addr+1);
}
char* push_imm16(char *addr, int i) {
*(int16_t*)addr = i;
return(addr+2);
}
#define push_mov8(a, b, c) push_imm8(push_imm8(a, 0xB0+b), c);
char* push_mov16(char* a, int b, int c) {
if (c) {
return(push_imm16(push_imm8(a, 0xB8+b), c));
} else {
// if value is 0 for 16-bit reg, xor it with itself
// saves a byte
return(push_imm16(a, 0xC031 | (b << 11) | (b << 8)));
}
}
char* push_jc(char* addr, char* target) {
int diff = target - addr;
return(push_imm8(push_imm8(addr, 0x72), diff-2));
}
char* push_jmp(char* addr, char* target) {
int diff = target - addr;
if (abs(diff)<0x70) {
return(push_imm8(push_imm8(addr, 0xEB), diff-2));
} else {
return(push_imm16(push_imm8(addr, 0xE9), diff-3));
}
}
int main(int argc, char** argv) {
// query mshowfat for first and last cluster number
// we expect the file to be contiguous
char output[64], cmd[256]= "mshowfat -i ";
strcat(cmd, argv[1]);
strcat(cmd, " '::");
strcat(cmd, argv[2]);
strcat(cmd, "'");
FILE* fd = popen(cmd, "r");
fgets(output, 64, fd);
int r = pclose(fd);
if (r > 0) {
perror("Unable to query mtools");
exit(1);
}
// parse the two numbers out of the output
// output is like "::kernel.bs <2-4>"
char* p = strchr(output, '<');
p++;
int min = strtol(p,&p,10);
int max = 0;
if (*p=='-') {
p++;
max = strtol(p,&p,10);
if (*p!='>') {
perror("Unexpected result from mshowfat");
exit(1);
}
} else {
max = min;
}
if (*p!='>') {
perror("Unexpected result from mshowfat");
exit(1);
}
fd = fopen(argv[1], "r+");
if (fd < 0) {
perror("Cant open disk image");
}
char bootsect[512];
if (fread(&bootsect, 512, 1, fd) < 1) {
perror("Failed to read bootsector");
exit(1);
}
// unpack fields from bpb
int ss = *((uint16_t*)(bootsect+0x0B));
int cs = *((uint8_t*)(bootsect+0x0D));
int rsc = *((uint16_t*)(bootsect+0x0E));
int fn = *((uint8_t*)(bootsect+0x10));
int rde = *((uint16_t*)(bootsect+0x11));
int fs = *((uint16_t*)(bootsect+0x16));
int spt = *((uint16_t*)(bootsect+0x18));
int nos = *((uint16_t*)(bootsect+0x1A));
int base = rsc + (fs * fn) + ((rde * 32) / ss);
int min_s = base + (min - 2) * cs;
int max_s = base + (max - 2) * cs + (cs - 1);
int bx = 0x100;
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int es = 0x60;
char* bs = (char*)&bootsect;
char* ptr = bs+0x3E;
char* putsfunc = ptr;
// assemble puts function
//ptr = push_imm16(ptr, 0xAC5E);
//ptr = push_imm16(ptr, 0xC084);
//ptr = push_imm16(ptr, 0x0874);
//ptr = push_imm16(ptr, 0x0EB4);
//ptr = push_imm16(ptr, 0xDB31);
//ptr = push_imm16(ptr, 0x10CD);
//ptr = push_imm16(ptr, 0xF3EB);
//ptr = push_imm16(ptr, 0xE6FF);
// assemble entry point to our main code
push_jmp(bs, ptr);
// assemble segment and stack setup
ptr = push_mov16(ptr, AX, es);
ptr = push_imm16(ptr, 0xD08E); // mov sp, ax
ptr = push_mov16(ptr, SP, 0);
// save two copies of our working segment on the stack
ptr = push_imm8(ptr, 0x50 + AX); // push ax
ptr = push_imm8(ptr, 0x50 + AX); // push ax
// assemble relocation code
ptr = push_mov16(ptr, AX, 0);
ptr = push_imm16(ptr, 0xD88E); // mov ds, ax
ptr = push_mov16(ptr, SI, 0x7C00);
ptr = push_imm16(ptr, 0xC08E); // mov es, ax
ptr = push_mov16(ptr, DI, (es-0x10) << 4);
ptr = push_mov16(ptr, CX, 0x0100);
ptr = push_imm16(ptr, 0xA5F3); // rep movsw (does the copy)
ptr = push_imm8(ptr, 0xEA); // jump far
ptr = push_imm16(ptr, ptr+4-bs+0x600);
ptr = push_imm16(ptr, 0);
// pop DS and ES from the stack
ptr = push_imm8(ptr, 0x07); // pop es
ptr = push_imm8(ptr, 0x1F); // pop ds
while(min_s <= max_s) {
int sector = (min_s % spt) + 1;
int tmp = min_s / spt;
int head = tmp % nos;
int track = tmp / nos;
int len = min(spt - sector, max_s - min_s)+1;
// memorize jump address in case of error
char* retry = ptr;
// set up registers for drive reset
ptr = push_imm8(push_imm8(ptr, 0xB0+AH), 0);
ptr = push_imm16(ptr, 0x13CD);
// set up registers for read call
ptr = push_imm16(push_imm8(ptr, 0xB8+AX), 0x0200 | len);
ptr = push_imm16(push_imm8(ptr, 0xB8+CX), sector | (track << 8));
ptr = push_imm8(push_imm8(ptr, 0xB0+DH), head);
ptr = push_imm16(push_imm8(ptr, 0xB8+BX), bx);
// set up read call
ptr = push_imm16(ptr, 0x13CD);
// jump if carry to retry addr
ptr = push_jc(ptr, retry);
min_s+=len;
bx=bx+(ss*len);
}
// emerg return addr
ptr = push_mov16(ptr, AX, 0);
ptr = push_imm8(ptr, 0x50 + AX);
ptr = push_imm8(ptr, 0xEA); // jmp far
ptr = push_imm16(ptr, 0x100);
ptr = push_imm16(ptr, es);
// emerg return int 0
ptr = bs + 0x100;
ptr = push_imm16(ptr, 0x18CD);
// write back bootsector
fseek(fd, 0, SEEK_SET);
if (fwrite(&bootsect, 512, 1, fd) < 1) {
perror("Failed to write back boot sector");
exit(1);
}
}