boot/freeldr/freeldr/arch/i386/entry.S

   1 /*
   2  *  FreeLoader
   3  *  Copyright (C) 1998-2002  Brian Palmer  <brianp@sginet.com>
   4  *
   5  *  This program is free software; you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation; either version 2 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  This program is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License along
  16  *  with this program; if not, write to the Free Software Foundation, Inc.,
  17  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18  */
  19
  20 #include <asm.inc>
  21 #include <arch/pc/x86common.h>
  22 #include <arch/pc/pcbios.h>
  23
  24 EXTERN _BootMain:PROC
  25 EXTERN _InitIdt:PROC
  26 EXTERN _i386Idt:DWORD
  27 //EXTERN _i386idtptr:FWORD
  28
  29 .code32
  30
  31 PUBLIC _RealEntryPoint
  32 _RealEntryPoint:
  33
  34         /* Setup segment selectors */
  35         mov ax, PMODE_DS
  36         mov ds, ax
  37         mov es, ax
  38         mov fs, ax
  39         mov gs, ax
  40         mov ss, ax
  41
  42     /* Setup protected mode stack */
  43         mov esp, dword ptr ds:[stack32]
  44
  45         /* Load the IDT */
  46 #ifdef _USE_ML
  47     lidt fword ptr ds:[i386idtptr]
  48 #else
  49         lidt i386idtptr
  50 #endif
  51
  52     /* Continue execution */
  53     jmp dword ptr ds:[ContinueAddress]
  54
  55 ContinueAddress:
  56     .long _FrldrStartup
  57
  58
  59 _FrldrStartup:
  60
  61     /* Store BootDrive and BootPartition */
  62         mov byte ptr ds:[_FrldrBootDrive], dl
  63         xor eax, eax
  64     mov al, dh
  65         mov dword ptr ds:[_FrldrBootPartition], eax
  66
  67     /* Patch long jump with real mode entry point */
  68     mov eax, dword ptr ds:[BSS_RealModeEntry]
  69     mov dword ptr ds:[SwitchToReal16Address], eax
  70
  71     /* Initialize the idt */
  72     call _InitIdt
  73
  74 #ifndef _USE_ML
  75     /* Clean out bss */
  76     xor eax, eax
  77     mov edi, offset __bss_start__
  78     mov ecx, offset __bss_end__ + 3
  79     sub ecx, edi
  80     shr ecx, 2
  81     rep stosd
  82
  83     /* Pass the command line to BootMain */
  84     mov eax, offset cmdline
  85 #else
  86     xor eax, eax
  87 #endif
  88
  89         /* GO! */
  90         push eax
  91         call _BootMain
  92
  93         /* We should never get here */
  94 stop:
  95         jmp     stop
  96         nop
  97         nop
  98
  99 Int386_regsin:
 100         .long 0
 101 Int386_regsout:
 102         .long 0
 103
 104 /*
 105  * int Int386(int ivec, REGS* in, REGS* out);
 106  */
 107 PUBLIC _Int386
 108 _Int386:
 109
 110         /* Get the function parameters */
 111         mov eax, dword ptr [esp + 4]
 112     mov dword ptr ds:[BSS_IntVector], eax
 113         mov eax, dword ptr [esp + 8]
 114         mov dword ptr [Int386_regsin], eax
 115         mov eax, dword ptr [esp + 12]
 116         mov dword ptr [Int386_regsout], eax
 117
 118         /* Save all registers + segment registers */
 119         push ds
 120         push es
 121         push fs
 122         push gs
 123         pusha
 124
 125     /* Copy input registers */
 126     mov esi, dword ptr [Int386_regsin]
 127     mov edi, BSS_RegisterSet
 128     mov ecx, REGS_SIZE / 4
 129     rep movsd
 130
 131     /* Set the function ID */
 132     mov bx, FNID_Int386
 133
 134     /* Set continue address and switch to real mode */
 135     mov dword ptr [ContinueAddress], offset Int386_return
 136     jmp SwitchToReal
 137
 138 Int386_return:
 139
 140     /* Copy output registers */
 141     mov esi, BSS_RegisterSet
 142     mov edi, dword ptr [Int386_regsout]
 143     mov ecx, REGS_SIZE / 4
 144     rep movsd
 145
 146     popa
 147     pop gs
 148     pop fs
 149     pop es
 150     pop ds
 151     ret
 152
 153
 154 /*
 155  * U16 PxeCallApi(U16 Segment, U16 Offset, U16 Service, VOID *Parameter);
 156  *
 157  * RETURNS:
 158  */
 159 PUBLIC _PxeCallApi
 160 _PxeCallApi:
 161     push ebp
 162     mov ebp, esp
 163
 164     pusha
 165     push es
 166
 167     /* copy entry point */
 168     mov eax, [ebp + 8]
 169     shl eax, 16
 170     mov ax, [ebp + 12]
 171     mov dword ptr ds:[BSS_PxeEntryPoint], eax
 172
 173     /* copy function */
 174     mov ax, [ebp + 16]
 175     mov word ptr ds:[BSS_PxeFunction], ax
 176
 177     /* convert pointer to data buffer to segment/offset */
 178     mov eax, [ebp + 20]
 179     shr eax, 4
 180     and eax, HEX(0f000)
 181     mov word ptr ds:[BSS_PxeBufferSegment], ax
 182     mov eax, [ebp + 20]
 183     and eax, HEX(0ffff)
 184     mov word ptr ds:[BSS_PxeBufferOffset], ax
 185
 186     /* Set the function ID and call realmode */
 187     mov bx, FNID_PxeCallApi
 188     call i386CallRealMode
 189
 190     pop es
 191     popa
 192
 193     mov esp, ebp
 194     pop ebp
 195
 196     mov ax, word ptr [BSS_PxeResult]
 197
 198     ret
 199
 200
 201 PUBLIC _Reboot
 202 _Reboot:
 203     /* Set the function ID */
 204     mov bx, FNID_Reboot
 205
 206     /*Switch to real mode (We don't return) */
 207     jmp SwitchToReal
 208
 209
 210 PUBLIC _ChainLoadBiosBootSectorCode
 211 _ChainLoadBiosBootSectorCode:
 212     /* Set the boot drive */
 213     mov dl, byte ptr [_FrldrBootDrive]
 214
 215     /* Set the function ID */
 216     mov bx, FNID_ChainLoadBiosBootSectorCode
 217
 218     /*Switch to real mode (We don't return) */
 219     jmp SwitchToReal
 220
 221
 222 PUBLIC i386CallRealMode
 223 i386CallRealMode:
 224     /* Set continue address and switch to real mode */
 225     mov dword ptr [ContinueAddress], offset i386CallRealMode_return
 226     jmp SwitchToReal
 227 i386CallRealMode_return:
 228     ret
 229
 230
 231 /* Entrypoint for realmode function calls
 232  * ContinueAddress must be set to the return point from realmode
 233  * bx must be set to the ID of the realmode function to call. */
 234 SwitchToReal:
 235     /* Set sane segments */
 236         mov ax, PMODE_DS
 237         mov ds, ax
 238         mov es, ax
 239         mov fs, ax
 240         mov gs, ax
 241         mov ss, ax
 242
 243         /* Save 32-bit stack pointer */
 244         mov dword ptr [stack32], esp
 245
 246         /* jmp to 16-bit segment to set the limit correctly */
 247     .byte HEX(0ea) // jmp far RMODE_CS:switch_to_real16
 248 SwitchToReal16Address:
 249     .long 0 // receives address of switch_to_real16
 250     .word RMODE_CS
 251     nop
 252
 253
 254         /* 16-bit stack pointer */
 255 stack16:
 256         .word   STACK16ADDR
 257
 258         /* 32-bit stack pointer */
 259 stack32:
 260         .long   STACK32ADDR
 261
 262     .align 4    /* force 4-byte alignment */
 263 gdt:
 264         /* NULL Descriptor */
 265         .word HEX(0000)
 266         .word HEX(0000)
 267         .word HEX(0000)
 268         .word HEX(0000)
 269
 270         /* 32-bit flat CS */
 271         .word HEX(FFFF)
 272         .word HEX(0000)
 273         .word HEX(9A00)
 274         .word HEX(00CF)
 275
 276         /* 32-bit flat DS */
 277         .word HEX(FFFF)
 278         .word HEX(0000)
 279         .word HEX(9200)
 280         .word HEX(00CF)
 281
 282         /* 16-bit real mode CS */
 283         .word HEX(FFFF)
 284         .word HEX(0000)
 285         .word HEX(9E00)
 286         .word HEX(0000)
 287
 288         /* 16-bit real mode DS */
 289         .word HEX(FFFF)
 290         .word HEX(0000)
 291         .word HEX(9200)
 292         .word HEX(0000)
 293
 294 /* GDT table pointer */
 295 gdtptr:
 296         .word HEX(27)           /* Limit */
 297         .long gdt                       /* Base Address */
 298
 299 /* Real-mode IDT pointer */
 300 rmode_idtptr:
 301         .word HEX(3ff)          /* Limit */
 302         .long 0                 /* Base Address */
 303
 304 PUBLIC i386idtptr
 305 i386idtptr:
 306     .word 255                   /* Limit */
 307     .long _i386Idt              /* Base Address */
 308
 309 PUBLIC _FrldrBootDrive
 310 _FrldrBootDrive:
 311     .byte 0
 312
 313 PUBLIC _FrldrBootPartition
 314 _FrldrBootPartition:
 315     .long 0
 316
 317 END