1 /* 2 * Implementation of a gateway into 32bit space. Stub functions 3 * can be called from Bochs BIOS which call functions with a compatible 4 * signature in 32bit space. All interrupts are disabled while in 5 * 32 bit mode. 6 * 7 * This library is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU Lesser General Public 9 * License as published by the Free Software Foundation; either 10 * version 2 of the License, or (at your option) any later version. 11 * 12 * This library is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 * Lesser General Public License for more details. 16 * 17 * You should have received a copy of the GNU Lesser General Public 18 * License along with this library; If not, see <http://www.gnu.org/licenses/>. 19 * 20 * Copyright (C) IBM Corporation, 2006 21 * Copyright (c) 2008, Citrix Systems, Inc. 22 * 23 * Author: Stefan Berger <stefanb@us.ibm.com> 24 * Author: Keir Fraser <keir@xen.org> 25 */ 26 27 /* 28 * Note: 29 * BCC's ABI does not require to preserve any 16bit registers ax, bx, cs, dx 30 * by a called function. So these registers need not be preserved while 31 * calling a function in 32bit space, either. 32 * 33 * When bcc calls a function with 16bit parameters it pushes 2 bytes onto 34 * the stack for such a parameter. GCC, however, expects 32bit parameters 35 * (4 bytes) even for uint16_t, so casting to 32bit from bcc is a good idea. 36 */ 37 38 /* At most 32 bytes in argument list to a 32-bit function. */ 39 #define MAX_ARG_BYTES 32 40 41 #define REAL_MODE_CODE_OFFSET 0xf0000 42 43 /* Definitions of code/data segment descriptors. */ 44 #define PM_32BIT_CS (gdt_entry_pm_32bit_cs - gdt_base) 45 #define PM_16BIT_CS (gdt_entry_pm_16bit_cs - gdt_base) 46 #define PM_32BIT_DS (gdt_entry_pm_32bit_ds - gdt_base) 47 #define PM_16BIT_DS (gdt_entry_pm_16bit_ds - gdt_base) 48 49 .align 16 50 gdt_base: 51 .word 0,0 52 .byte 0,0,0,0 53 gdt_entry_pm_32bit_cs: 54 .word 0xffff, 0x0000 55 .byte 0x00, 0x9b, 0xcf, 0x00 56 gdt_entry_pm_16bit_cs: 57 .word 0xffff, 0x0000 58 .byte REAL_MODE_CODE_OFFSET >> 16, 0x9b, 0x8f, 0x0 59 gdt_entry_pm_32bit_ds: 60 .word 0xffff, 0x0000 61 .byte 0x0, 0x93, 0xcf, 0x0 62 gdt_entry_pm_16bit_ds: 63 .word 0xffff, 0x0000 64 .byte 0x0, 0x93, 0x8f, 0x0 65 gdt_entry_end: 66 67 protmode_gdtdesc: 68 .word (gdt_entry_end - gdt_base) - 1 69 .long gdt_base | REAL_MODE_CODE_OFFSET 70 71 realmode_gdtdesc: 72 .word 0xffff 73 .long 0x0 74 75 Upcall: 76 ; Do an upcall into 32 bit space 77 ; 78 ; Input: 79 ; bx: index of function to call 80 ; Ouput: 81 ; dx, ax: 32 bit result of call (even if 'void' is expected) 82 83 ; Save caller state, stack frame offsets listed below 84 #define esp_off 0 85 #define ss_off 4 86 #define es_off 6 87 #define ds_off 8 88 #define flags_off 10 89 #define retaddr_off 12 90 #define args_off 14 91 pushf 92 cli 93 push ds 94 push es 95 push ss 96 push esp 97 98 ; Calculate protected-mode esp from ss:sp 99 and esp, #0xffff 100 xor eax, eax 101 mov ax, ss 102 shl eax, #4 103 add esp, eax 104 105 ; Switch to protected mode 106 seg cs 107 lgdt protmode_gdtdesc 108 mov eax, cr0 109 or al, #0x1 ; protected mode on 110 mov cr0, eax 111 jmpf DWORD (REAL_MODE_CODE_OFFSET|upcall1), #PM_32BIT_CS 112 upcall1: 113 USE32 114 mov ax, #PM_32BIT_DS 115 mov ds, ax 116 mov es, ax 117 mov ss, ax 118 119 ; Marshal arguments and call 32-bit function 120 mov ecx, #MAX_ARG_BYTES/4 121 upcall2: 122 push MAX_ARG_BYTES-4+args_off[esp] 123 loop upcall2 124 mov eax, [BIOS_INFO_PHYSICAL_ADDRESS + BIOSINFO_OFF_bios32_entry] 125 call eax 126 add esp, #MAX_ARG_BYTES 127 mov ecx, eax ; Result in ecx 128 129 ; Restore real-mode stack pointer 130 xor eax, eax 131 mov ax, ss_off[esp] 132 mov bx, ax ; Real-mode ss in bx 133 shl eax, 4 134 sub esp, eax 135 136 ; Return to real mode 137 jmpf upcall3, #PM_16BIT_CS 138 upcall3: 139 USE16 140 mov ax, #PM_16BIT_DS 141 mov ds, ax 142 mov es, ax 143 mov ss, ax 144 mov eax, cr0 145 and al, #0xfe ; protected mode off 146 mov cr0, eax 147 jmpf upcall4, #REAL_MODE_CODE_OFFSET>>4 148 upcall4: 149 seg cs 150 lgdt realmode_gdtdesc 151 152 ; Restore real-mode ss 153 mov ss, bx 154 155 ; Convert result into dx:ax format 156 mov eax, ecx 157 ror eax, #16 158 mov dx, ax 159 ror eax, #16 160 161 ; Restore caller state and return 162 pop esp 163 pop bx ; skip ss 164 pop es 165 pop ds 166 popf 167 ret 168 169 MACRO DoUpcall 170 mov bx, #?1 171 jmp Upcall 172 MEND 173 174 #define X(idx, ret, fn, args...) _ ## fn: DoUpcall(idx) 175 #include "32bitprotos.h" 176 #undef X 177