boot/freeldr/freeldr/arch/realmode/amd64.S

   1
   2 #include <asm.inc>
   3 #include "../../include/arch/pc/x86common.h"
   4
   5 #define IMAGE_DOS_HEADER_e_lfanew 60
   6 #define IMAGE_FILE_HEADER_SIZE 20
   7 #define IMAGE_OPTIONAL_HEADER_AddressOfEntryPoint 16
   8
   9 .code16
  10
  11 /* fat helper code */
  12 #include "fathelp.inc"
  13
  14 .org 512
  15 Startup:
  16
  17     cli
  18
  19     /* Setup real mode segment registers */
  20     xor ax, ax
  21     mov ds, ax
  22     mov es, ax
  23     mov fs, ax
  24     mov gs, ax
  25     mov ss, ax
  26
  27     /* Save the boot drive and partition */
  28     mov byte ptr ds:[BSS_BootDrive], dl
  29     mov byte ptr ds:[BSS_BootPartition], dh
  30
  31     /* Setup a real mode stack */
  32     mov sp, word ptr ds:[stack16]
  33
  34     /* Output first status */
  35     mov si, offset Msg_Starting
  36     call writestr
  37
  38     /* Enable A20 address line */
  39     call EnableA20
  40
  41     /* Check the CPU */
  42     call CheckFor64BitSupport
  43     test al, al
  44     jnz .LongModeSupported
  45
  46     /* Output failure message */
  47     mov si, offset Msg_Unsupported
  48     call writestr
  49
  50     /* Wait for a keypress */
  51     int HEX(16)
  52     jmp Reboot
  53
  54 Msg_Unsupported:
  55     .ascii "This CPU is not supported.", CR, LF
  56     .ascii "Press any key to reboot...", NUL
  57
  58 Msg_Starting:
  59     .ascii "Starting FreeLoader...", CR, LF, NUL
  60
  61 Msg_LongModeSupported:
  62     .ascii "Long mode support detected.", CR, LF, NUL
  63
  64 .LongModeSupported:
  65     /* Output status */
  66     mov si, offset Msg_LongModeSupported
  67     call writestr
  68
  69     /* Load the GDT */
  70     lgdt fword ptr [gdtptr]
  71
  72     /* Build the startup page tables */
  73     call BuildPageTables
  74
  75     /* Store real mode entry point in shared memory */
  76     mov dword ptr ds:[BSS_RealModeEntry], offset RealModeEntryPoint
  77
  78     /* Address the image with es segment */
  79     mov ax, FREELDR_PE_BASE / 16
  80     mov es, ax
  81
  82     /* Get address of optional header */
  83     mov eax, dword ptr es:[IMAGE_DOS_HEADER_e_lfanew]
  84     add eax, 4 + IMAGE_FILE_HEADER_SIZE
  85
  86     /* Get address of entry point */
  87     mov eax, dword ptr es:[eax + IMAGE_OPTIONAL_HEADER_AddressOfEntryPoint]
  88     add eax, FREELDR_PE_BASE
  89
  90     /* Save entry point */
  91     mov dword ptr ds:[LongModeEntryPoint], eax
  92
  93     /* Restore es */
  94     xor ax, ax
  95     mov es, ax
  96
  97     /* Output status */
  98     mov si, offset Msg_SwitchToLongMode
  99     call writestr
 100
 101     jmp ExitToLongMode
 102
 103 Msg_SwitchToLongMode:
 104     .ascii "Switching to long mode....", CR, LF, NUL
 105
 106 .align 8
 107 gdt:
 108     .word HEX(0000), HEX(0000), HEX(0000), HEX(0000) /* 00: NULL descriptor */
 109     .word HEX(0000), HEX(0000), HEX(0000), HEX(0000) /* 08:  */
 110     .word HEX(0000), HEX(0000), HEX(9800), HEX(0020) /* 10: long mode cs */
 111     .word HEX(ffff), HEX(0000), HEX(f300), HEX(00cf) /* 18: long mode ds */
 112     .word HEX(FFFF), HEX(0000), HEX(9E00), HEX(0000) /* 20: 16-bit real mode CS */
 113     .word HEX(FFFF), HEX(0000), HEX(9200), HEX(0000) /* 28: 16-bit real mode DS */
 114     .word HEX(FFFF), HEX(0000), HEX(9B00), HEX(00CF) /* 30: compat mode cs */
 115
 116 /* GDT table pointer */
 117 gdtptr:
 118     .word HEX(37) /* Limit */
 119     .long offset gdt   /* Base Address */
 120
 121
 122 CheckFor64BitSupport:
 123     /* Check if CPU supports CPUID */
 124     pushad
 125     pushfd
 126     pop eax
 127     mov ebx, eax
 128     xor eax, HEX(00200000)
 129     push eax
 130     popfd
 131     pushfd
 132     pop eax
 133     cmp eax,ebx
 134     jnz .CheckForPAE
 135
 136     mov si, offset .Msg_NoCpuidSupport
 137     call writestr
 138     popad
 139     xor al, al
 140     ret
 141
 142 .Msg_NoCpuidSupport:
 143     .ascii "The system doesn't support CPUID.", CR, LF, NUL
 144
 145 .CheckForPAE:
 146     /* CPUID support detected - getting the PAE/PGE */
 147     mov eax,1 // Fn0000_0001 - PAE in EDX[6]
 148     cpuid
 149     and edx, HEX(00a0)
 150     cmp edx, HEX(00a0)
 151     je .CheckForLongMode
 152
 153     mov si, offset .Msg_NoPAE
 154     call writestr
 155     popad
 156     xor al, al
 157     ret
 158
 159 .Msg_NoPAE:
 160     .ascii "PAE or PGE not set.", CR, LF, NUL
 161
 162 .CheckForLongMode:
 163     xor edx, edx
 164     mov eax, HEX(80000001)
 165     cpuid
 166     and edx, HEX(20000000)
 167     test edx,edx
 168     jnz .Success
 169
 170     mov si, offset .Msg_NoLongMode
 171     call writestr
 172     popad
 173     xor al, al
 174     ret
 175
 176 .Msg_NoLongMode:
 177     .ascii "Long mode is not supported.", CR, LF, NUL
 178
 179 .Success:
 180     popad
 181     xor al, al
 182     inc al
 183     ret
 184
 185
 186 BuildPageTables:
 187     pusha
 188     push es
 189
 190     /* Get segment of the PML4 */
 191     mov eax, PML4_ADDRESS / 16
 192     mov es, ax
 193     cld
 194     xor di, di
 195
 196     /* One entry in the PML4 pointing to PDP */
 197     mov eax, PDP_ADDRESS
 198     or eax, HEX(0f)
 199     stosd
 200
 201     /* clear rest */
 202     xor eax, eax
 203     mov cx, 1023
 204     rep stosd
 205
 206     /* One entry in the PDP pointing to PD */
 207     mov eax, PD_ADDRESS
 208     or eax, HEX(0f)
 209     stosd
 210
 211     /* clear rest */
 212     xor eax, eax
 213     mov ecx, 1023
 214     rep stosd
 215
 216     /* 512 entries in the PD, each defining a 2MB page each */
 217     mov ecx, 512
 218     mov eax, HEX(008f)
 219
 220 .Bpt2:
 221     mov es: [di], eax
 222     mov dword ptr es: [di + 4], 0
 223     add eax, 512 * 4096 // add 512 4k pages
 224     add di, 8
 225
 226     /* Loop all PDEs */
 227     dec cx
 228     jnz .Bpt2
 229
 230     /* Return */
 231     pop es
 232     popa
 233     ret
 234
 235
 236 /******************************************************************************/
 237
 238 #define MSR_EFER HEX(C0000080)
 239 #define LMODE_CS HEX(10)
 240
 241 /* This is the entry point from long mode */
 242 RealModeEntryPoint:
 243     /* Disable Protected Mode */
 244     mov eax, cr0
 245     and eax, HEX(0fffffffe) // ~0x00000001
 246     mov cr0, eax
 247
 248     /* Clear prefetch queue & correct CS */
 249     ljmp16 0, offset InRealMode
 250
 251 InRealMode:
 252
 253 //    mov ax, HEX(0b800)
 254 //    mov es, ax
 255 //    mov word ptr es:[12], HEX(0e00) + '6'
 256
 257     /* Set real mode segments */
 258     xor ax, ax
 259     mov ds, ax
 260     mov es, ax
 261     mov fs, ax
 262     mov gs, ax
 263     mov ss, ax
 264
 265     /* Clear out the high 16-bits of ESP */
 266     /* This is needed because I have one */
 267     /* machine that hangs when booted to dos if */
 268     /* anything other than 0x0000 is in the high */
 269     /* 16-bits of ESP. Even though real-mode */
 270     /* code should only use SP and not ESP. */
 271     xor esp, esp
 272
 273     /* Restore real mode stack */
 274     mov sp, word ptr ds:[stack16]
 275
 276     // sti /* These are ok now */
 277
 278     /* Do the callback, specified by bx */
 279     shl bx, 1
 280     call word ptr ds:CallbackTable[bx]
 281
 282 ExitToLongMode:
 283     /* Disable interrupts */
 284     cli
 285
 286     /* Set correct segment registers */
 287     xor ax,ax
 288     mov ds,ax
 289     mov es,ax
 290     mov fs,ax
 291     mov gs,ax
 292     mov ss,ax
 293
 294     /* Save current stack pointer */
 295     mov word ptr ds:[stack16], sp
 296
 297     /* Set PAE and PGE: 10100000b */
 298     mov eax, HEX(00a0)
 299     mov cr4, eax
 300
 301     /* Point cr3 at the PML4 */
 302     mov eax, PML4_ADDRESS
 303     mov cr3, eax
 304
 305     /* Enable long mode */
 306     mov ecx, MSR_EFER
 307     rdmsr
 308     or eax, HEX(00000100)
 309     wrmsr
 310
 311     /* Activate long mode by enabling paging and protection simultaneously,
 312        skipping protected mode entirely */
 313     mov eax, cr0
 314     or eax, HEX(80000001)
 315     mov cr0, eax
 316
 317     /* Clear prefetch queue & correct CS */
 318     ljmp16 LMODE_CS, InLongMode
 319 InLongMode:
 320     //DB 66h, 0B8h, 18h, 00h // mov ax, LMODE_DS
 321     //DB 66h, 8Eh, 0D8h // mov ds, ax
 322     //DB 66h, 66h, 0C7h, 04h, 25h, 00h, 80h, 0Bh, 00h, 31h, 0Eh
 323     //mov word ptr [HEX(b8000)], HEX(0e00) + '1'
 324
 325     .byte HEX(0ff), HEX(25) // opcode of 64bit indirect jump
 326     .long 1 // relative address of LongModeEntryPoint
 327     nop
 328 LongModeEntryPoint:
 329     .long 0, 0
 330
 331     int HEX(16)
 332     jmp Reboot
 333
 334 CallbackTable:
 335     .word Int386
 336     .word Reboot
 337     .word ChainLoadBiosBootSectorCode
 338     .word PxeCallApi
 339     .word PnpBiosGetDeviceNodeCount
 340     .word PnpBiosGetDeviceNode
 341     .word 0 // BootLinuxKernel
 342
 343     /* 16-bit stack pointer */
 344 stack16:
 345     .word STACK16ADDR
 346
 347
 348 #include "int386.inc"
 349 #include "pxe.inc"
 350 #include "pnp.inc"
 351 #include "helpers.inc"
 352
 353 .org (FREELDR_PE_BASE - FREELDR_BASE - 1)
 354 .byte 0
 355 .endcode16
 356
 357 END