Stackoverflow 76807564

bios.h:


#ifndef _BIOS_H
#define _BIOS_H

#include <stdint.h>

/* Externally callable version of function
   Try changing to __cdecl, __watcall etc and
   watch how the generated code changes
 */

extern void __pascal bios_print_string (const char *string);

/* Functions with suffix _i are inlined functions */
static inline void bios_print_char_page_i (uint8_t inchar, uint16_t page_color);
#pragma aux bios_print_char_page_i = \
    "mov ah, 0x0e"   \
    "int 0x10"       \
    modify [ah]      \
    parm   [al][bx]

static inline void bios_print_string_i (const char *string)
{
    char ch;
    /* Print characters with BIOS until NUL character is reached */
    while (ch = *string++)
        bios_print_char_page_i (ch, 0x0001);

    return;
}

#endif /* _BIOS_H */

bios.c:

#include "bios.h"
#include <stdint.h>

void bios_print_string (const char *string)
{
    bios_print_string_i (string);

    return;
}


boot.c:

#include "bios.h"
#include <stdint.h>

#pragma aux BOOTCALL "*_" parm [DX];

#pragma aux (BOOTCALL) kernelMain;
void __declspec ( noreturn ) kernelMain (uint8_t drivenum);

#pragma aux (BOOTCALL) init;
void __declspec ( naked ) init (uint8_t drivenum)
{
    (void)drivenum;
    __asm {
        mov bp, 7C00h
        xor ax, ax
        mov ds, ax
        mov es, ax
        mov ss, ax
        mov sp, bp
        jmp kernelMain
    }
}

void kernelMain (uint8_t drivenum)
{
    /* Call an inline version of bios_print_string */
    bios_print_string_i ("Booted from ");

    /* Call a non-inlined version of bios_print_string */
    if (drivenum < 0x80)
        bios_print_string ("Floppy\r\n");
    else
        bios_print_string ("Hard Drive\r\n");

    /* End with infinite loop */
    while (1) __asm { hlt };
}


Build with:

wcc -d0 -ohls -ms -wx -s -ecc -zl -2 boot.c
wcc -d0 -ohls -ms -wx -s -ecc -zl -2 bios.c
wlink file boot.o file bios.o format raw bin \
    name test.bin option NODEFAULTLIBS,verbose,OFFSET=0x7C00