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/* Project:     OSLib
 * Description: The OS Construction Kit
 * Date:                1.6.2000
 * Idea by:             Luca Abeni & Gerardo Lamastra
 *
 * OSLib is an SO project aimed at developing a common, easy-to-use
 * low-level infrastructure for developing OS kernels and Embedded
 * Applications; it partially derives from the HARTIK project but it
 * currently is independently developed.
 *
 * OSLib is distributed under GPL License, and some of its code has
 * been derived from the Linux kernel source; also some important
 * ideas come from studying the DJGPP go32 extender.
 *
 * We acknowledge the Linux Community, Free Software Foundation,
 * D.J. Delorie and all the other developers who believe in the
 * freedom of software and ideas.
 *
 * For legalese, check out the included GPL license.
 */

/* The first things to do when an OSLib application starts :    */
/* Set up segment registers & stack; then execute startup code  */
/* When the application returns the gate-jmp make us return to  */
/* RM through X interface!                                      */

/* Use X standard GDT selectors */
#include <ll/i386/sel.h>
#include <ll/i386/linkage.h>
#include <ll/i386/defs.h>
#include <ll/i386/mb-hdr.h>

/* #define __DEBUG__ */

#ifdef __LINUX__ /* ELF mode */
#define MULTIBOOT_FLAGS (MULTIBOOT_MEMORY_INFO)
#else /* else it is COFF! */
#define MULTIBOOT_FLAGS (MULTIBOOT_MEMORY_INFO | MULTIBOOT_AOUT_KLUDGE)
#endif

.extern SYMBOL_NAME(_startup)
.extern SYMBOL_NAME(_stkbase)
.extern SYMBOL_NAME(_stktop)

.extern SYMBOL_NAME(halt)

.data

ASMFILE(X0)

.globl SYMBOL_NAME(IDT)
.globl SYMBOL_NAME(GDT_base)
.globl SYMBOL_NAME(mb_signature)
.globl SYMBOL_NAME(mbi)

/* GDT Definition */
GDT:
.word   0,0,0,0         /* X_NULL_SEL */
.word   0,0,0,0         /* X_DATA16_SEL */
.word   0,0,0,0         /* X_CODE16_SEL */
.word   0,0,0,0         /* X_CODE32_SEL */
                        /* X_RM_BACK_GATE */
rmBckGateFix1:          /* X_FLATCODE_SEL */
.word   0
.word   X_FLATCODE_SEL  
.word   0x8C00
rmBckGateFix2:
.word   0

.word   0,0,0,0         /* X_PM_BACK_GATE */
.word   0xFFFF          /* X_FLATDATA_SEL */ 
.word   0
.word   0x9200
.word   0x00CF
.word   0xFFFF          /* X_FLATCODE_SEL */ 
.word   0
.word   0x9A00
.word   0x00CF
.word   0,0,0,0         /* X_CALLBIOS_SEL */
.word   0,0,0,0         /* X_CALLBIOS_GATE */
.word   0,0,0,0         /* X_VM86_TSS */
.word   0,0,0,0         /* X_MAIN_TSS */
        .fill 256 - 12,8,0
        
GDT_descr:
.word 256*8-1 
SYMBOL_NAME_LABEL(GDT_base) 
.long GDT

IDT_descr:
        .word 256*8-1           # idt contains 256 entries
        .long SYMBOL_NAME(IDT)

/* MultiBoot Data Stuff definition */
SYMBOL_NAME_LABEL(mb_signature) .long 0
SYMBOL_NAME_LABEL(mbi) .long 0

.bss            /* This MUST be in the BSS !!! */
/* IDT definition */
SYMBOL_NAME_LABEL(IDT)
        .fill 256,8,0           # idt is uninitialized

/* Protected mode stack */
base:
.space  8192,0
tos:

.text
.globl  SYMBOL_NAME(_start)
.globl SYMBOL_NAME(__exit)
.globl  SYMBOL_NAME(start)
.globl start

SYMBOL_NAME_LABEL(_start)
SYMBOL_NAME_LABEL(start)
start:
.align          8
/*start:*/
                jmp     boot_entry              
                /* 
                Here we go with the multiboot header... 
                ---------------------------------------
                */              
.align          8
boot_hdr:
.align          8
                .long   MULTIBOOT_MAGIC
                .long   MULTIBOOT_FLAGS
                /* Checksum */
                .long   -(MULTIBOOT_MAGIC+MULTIBOOT_FLAGS)
#ifndef __LINUX__ /* COFF mode */
                .long   boot_hdr
/*              .long   SYMBOL_NAME(start)*/
                .long   start
                .long   _edata
                .long   _end
                .long   boot_entry
#endif 
                                
boot_entry:     /* Just a brief debug check */  
                #ifdef __DEBUG__
                /* A Brown 1 should appear... */
                    movl        $0xB8000,%edi
                    addl        $158,%edi
                    movb        $'1',%gs:0(%edi)
                    incl        %edi
                    movb        $6,%gs:0(%edi)
                #endif
                
                /* 
                 * Hopefully if it gets here, CS & DS are
                 * Correctly set for FLAT LINEAR mode
                 */
                /* Test if GDT is usable */
                movl    %gs:0(%ebx),%ecx
                andl    $0x0200,%ecx    /* MB_INFO_BOOT_LOADER_NAME */
movl    $0xB8000,%edi
addl    $150,%edi
movb    $'1',%gs:0(%edi)
incl    %edi
movb    $6,%gs:0(%edi)
                jz      GDT_is_not_OK
incl    %edi
movb    $'2',%gs:0(%edi)
incl    %edi
movb    $6,%gs:0(%edi)

                movl    %gs:64(%ebx), %ebp /* Name Address... */
                cmpb    $'X', %gs:0(%ebp)
                je      GDT_is_OK
GDT_is_not_OK:
                /* 
                 * Fix the X_RM_BACK_GATE with the address of halt()
                */

/* Now I test if the check mechanism is OK... */
                movl    $SYMBOL_NAME(halt),%eax
                movw    %ax,%gs:rmBckGateFix1
                shrl    $16,%eax
                movw    %ax,%gs:rmBckGateFix2
                
                /* Load GDT, using the predefined assignment! */
                lgdt    GDT_descr
movl    $0xB8000,%edi
addl    $146,%edi
movb    $'0',%gs:0(%edi)
incl    %edi
movb    $6,%gs:0(%edi)
                
GDT_is_OK:      movw    $(X_FLATDATA_SEL),%ax
                movw    %ax,%ds
                movw    %ax,%es
                movw    %ax,%ss
                movw    %ax,%fs
                movw    %ax,%gs
                movl    $tos,%esp
                movl    $base,SYMBOL_NAME(_stkbase)
                movl    $tos,SYMBOL_NAME(_stktop)
                
                /* Store the MULTIBOOT informations */
                movl    %eax,SYMBOL_NAME(mb_signature)
                movl    %ebx,SYMBOL_NAME(mbi)
                
                /* Store the X passed GDT address!
                 * If GDT is not available is a dummy instruction!
                 */
                sgdt    GDT_descr

                /* Now probably is the case to load CS... */
                ljmp $X_FLATCODE_SEL, $load_cs

load_cs:
                /* Load IDT */
                lidt    IDT_descr
                
                cld
                call SYMBOL_NAME(_startup)
        
                /* Well I hope when I reach this
                   The X_RM_BACK_GATE has been setup correctly
                   even if the kernel has not been loaded through X!
                */
                .byte   0x0EA              /* Direct gate jmp */
                .long   0
                .word   X_RM_BACK_GATE

/* Simple function to terminate PM application  */

/* void __exit(int code)                                */

SYMBOL_NAME_LABEL(__exit)
                pushl   %ebp
                movl    %esp,%ebp                       
                movl    8(%ebp),%eax
                .byte   0x0ea              /* Direct gate jmp */
                .long   0  
                .word   X_RM_BACK_GATE