/* $NetBSD: biostramp.S,v 1.14 2008/04/28 20:23:23 martin Exp $ */ /*- * Copyright (c) 1996 The NetBSD Foundation, Inc. * All rights reserved. * * This code is derived from software contributed to The NetBSD Foundation * by John Kohl. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */ /* * biostramp.S: provide a means for NetBSD to call BIOS interrupts * by switching to real mode, calling it, and switching * back to protected & paging mode. */ /* * Micro$haft's book on i386/i486 programming says you should do the following * to return to real mode from protected mode: * * 1) disable paging, by jumping to code with identical virtual and physical * addresses, clearing PG in CR0, and zeroing CR3 (PDBR). * * 2) segment descriptors must be byte-granular with limit 64k-1, def32 = 0, * (i.e. 16-bit data accesses and/or 80286 instructions) * CS must be executable; DS,ES,FS,GS should be writable * * 3) disable interrupts, load IDTR with original value (base 0, limit 1023) * * 4) clear PE in CR0, execute FAR jump to load CS. * * 5) load SP, and off you go * */ #include "assym.h" #include #include #include #include #include #include #define addr32 .byte 0x67 #define data32 .byte 0x66 .set MYBASE,NBPG .set MYSCRATCH,NBPG*2 .set CR3_ADDR,(MYSCRATCH-4) .set IDTR_SAVE_ADDR,CR3_ADDR-6 .set GDTR_SAVE_ADDR,IDTR_SAVE_ADDR-6 .set GDTR_LOCAL_ADDR,GDTR_SAVE_ADDR-6 .set STACK_PTR_ADDR,GDTR_LOCAL_ADDR-4 .set BASE_PTR_ADDR,STACK_PTR_ADDR-4 .set FUNCTION_ADDR,(BASE_PTR_ADDR-2) .set GDT_COPY_ADDR,(FUNCTION_ADDR-NGDT*8) .set EAX_REGADDR,(GDT_COPY_ADDR-4) .set EBX_REGADDR,(EAX_REGADDR-4) .set ECX_REGADDR,(EBX_REGADDR-4) .set EDX_REGADDR,(ECX_REGADDR-4) .set ESI_REGADDR,(EDX_REGADDR-4) .set EDI_REGADDR,(ESI_REGADDR-4) .set EFLAGS_REGADDR,(EDI_REGADDR-4) .set ES_REGADDR, (EFLAGS_REGADDR-4) .set ENDREGADDR,(ES_REGADDR-4) .set REALSTACK,ENDREGADDR-20 # leave a red zone? #define COPY_FLAGS (PSL_C|PSL_PF|PSL_AF|PSL_Z|PSL_N|PSL_D|PSL_V) /* * do_bios_call(int function, struct bioscall *regs) */ ENTRY(do_bios_call) pushl %ebp movl %esp,%ebp /* set up frame ptr */ pushl %esi pushl %edi pushl %ebx pushl %ds pushl %es pushl %fs pushl %gs # copy data to where the real-mode hook can handle it movl 8(%ebp),%eax movw %ax,FUNCTION_ADDR movl 12(%ebp),%ebx movl BIOSCALLREG_EAX(%ebx),%eax movl %eax,EAX_REGADDR movl BIOSCALLREG_EBX(%ebx),%eax movl %eax,EBX_REGADDR movl BIOSCALLREG_ECX(%ebx),%eax movl %eax,ECX_REGADDR movl BIOSCALLREG_EDX(%ebx),%eax movl %eax,EDX_REGADDR movl BIOSCALLREG_ESI(%ebx),%eax movl %eax,ESI_REGADDR movl BIOSCALLREG_EDI(%ebx),%eax movl %eax,EDI_REGADDR # merge current flags with certain provided flags movl BIOSCALLREG_EFLAGS(%ebx),%ecx pushfl popl %eax andl $~(COPY_FLAGS|PSL_I),%eax andl $COPY_FLAGS,%ecx orl %ecx,%eax movl %eax,EFLAGS_REGADDR movl $0, ES_REGADDR # save flags, disable interrupts, do real mode stuff pushfl # save GDT sgdt GDTR_SAVE_ADDR # copy the GDT to local area movl GDTR_SAVE_ADDR+2,%esi movl $GDT_COPY_ADDR,%edi movl $(NGDT*8),%ecx cld rep movsb movw $(NGDT*8)-1,GDTR_LOCAL_ADDR movl $GDT_COPY_ADDR,GDTR_LOCAL_ADDR+2 # install GDT copy lgdt GDTR_LOCAL_ADDR cli # save IDT sidt IDTR_SAVE_ADDR # set up new stack: save old ones, create new segs movl %esp,STACK_PTR_ADDR movl %ebp,BASE_PTR_ADDR movl $REALSTACK,%esp movl $0,%ebp # leave no trace, there is none. # save CR3 movl %cr3,%eax movl %eax,CR3_ADDR # turn off paging movl %cr0,%eax andl $~(CR0_PG),%eax movl %eax,%cr0 # flush TLB, drop PDBR xorl %eax,%eax movl %eax,%cr3 ## load 16-bit segment descriptors movw $GSEL(GBIOSDATA_SEL,SEL_KPL),%bx movw %bx,%ds movw %bx,%es movw %bx,%fs movw %bx,%gs ljmp $GSEL(GBIOSCODE_SEL,SEL_KPL),$x16+MYBASE x16: # turn off protected mode--yikes! mov %cr0,%eax data32 and $~CR0_PE,%eax mov %eax,%cr0 # need inter-segment jump to reload real-mode CS data32 ljmp $(MYBASE>>4),$xreal xreal: # really in real mode now # set up segment selectors. Note: everything is now relative # to zero-base in this file, except %ss. # data items in our scratch area need to reflect MYADDR xorl %eax,%eax movw %ax,%ss movw %cs,%ax movw %ax,%es movw %ax,%fs movw %ax,%gs movw %ax,%ds ## load IDT, now that we are here. addr32 lidt IDT_bios # Don't forget that we're in real mode, with 16-bit default data. # all these movl's are really movw's, and movw's are movl's! addr32 movw EDI_REGADDR-MYBASE,%di addr32 movw ESI_REGADDR-MYBASE,%si addr32 movw EDX_REGADDR-MYBASE,%dx addr32 movw ECX_REGADDR-MYBASE,%cx addr32 movw EBX_REGADDR-MYBASE,%bx addr32 movb FUNCTION_ADDR-MYBASE,%al addr32 movb %al,intaddr+1 # self modifying code, yuck. no indirect interrupt instruction! # long jump to flush processor cache to reflect code modification data32 ljmp $(MYBASE>>4),$flushit flushit: addr32 movw EFLAGS_REGADDR-MYBASE,%ax pushl %eax popfl addr32 movw EAX_REGADDR-MYBASE,%ax intaddr: int $0xff # save results pushf addr32 movw %ax,EAX_REGADDR-MYBASE addr32 movw %bx,EBX_REGADDR-MYBASE addr32 movw %cx,ECX_REGADDR-MYBASE addr32 movw %dx,EDX_REGADDR-MYBASE addr32 movw %si,ESI_REGADDR-MYBASE addr32 movw %di,EDI_REGADDR-MYBASE pop %ax addr32 movw %ax,EFLAGS_REGADDR-MYBASE addr32 movw %es,ES_REGADDR-MYBASE # and return to protected mode cli # just to be sure mov %cr0,%eax data32 or $CR0_PE,%eax mov %eax,%cr0 # long jump to 32-bit code segment data32 ljmp $GSEL(GCODE_SEL,SEL_KPL),$x32+MYBASE x32: #back in 32-bit mode/protected mode (but not paging yet). # Reload the segment registers & IDT movw $GSEL(GDATA_SEL,SEL_KPL),%bx movw %bx,%ds movw %bx,%ss movw %bx,%es # reload PDBR movl CR3_ADDR,%eax movl %eax,%cr3 movl %cr0,%eax orl $CR0_PG,%eax movl %eax,%cr0 # reload system copy of GDT lgdt GDTR_SAVE_ADDR # restore protected-mode stack movl STACK_PTR_ADDR,%esp movl BASE_PTR_ADDR,%ebp #restore protected-mode IDT lidt IDTR_SAVE_ADDR # copy back arguments from holding pen movl 12(%ebp),%ebx movl EAX_REGADDR,%eax movl %eax,BIOSCALLREG_EAX(%ebx) movl EBX_REGADDR,%eax movl %eax,BIOSCALLREG_EBX(%ebx) movl ECX_REGADDR,%eax movl %eax,BIOSCALLREG_ECX(%ebx) movl EDX_REGADDR,%eax movl %eax,BIOSCALLREG_EDX(%ebx) movl ESI_REGADDR,%eax movl %eax,BIOSCALLREG_ESI(%ebx) movl EDI_REGADDR,%eax movl %eax,BIOSCALLREG_EDI(%ebx) movl EFLAGS_REGADDR,%eax movl %eax,BIOSCALLREG_EFLAGS(%ebx) movl ES_REGADDR, %eax movl %eax,BIOSCALLREG_ES(%ebx) # finish up, restore registers, and return popfl popl %gs popl %fs popl %es popl %ds # see above popl %ebx popl %edi popl %esi leave ret #ifdef __ELF__ .align 16 #else .align 4 #endif IDT_bios: # BIOS IDT descriptor (real-mode) .word 1023 .long 0