/* $NetBSD: start_dos.S,v 1.2 2024/09/11 20:15:36 andvar Exp $ */ /* * startup for DOS .COM programs * with input from: * netbsd:sys/arch/i386/boot/start.S * Tor Egge's patches for NetBSD boot (pr port-i386/1002) * freebsd:sys/i386/boot/netboot/start2.S */ /* * Ported to boot 386BSD by Julian Elischer (julian@tfs.com) Sept 1992 * * Mach Operating System * Copyright (c) 1992, 1991 Carnegie Mellon University * All Rights Reserved. * * Permission to use, copy, modify and distribute this software and its * documentation is hereby granted, provided that both the copyright * notice and this permission notice appear in all copies of the * software, derivative works or modified versions, and any portions * thereof, and that both notices appear in supporting documentation. * * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. * * Carnegie Mellon requests users of this software to return to * * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU * School of Computer Science * Carnegie Mellon University * Pittsburgh PA 15213-3890 * * any improvements or extensions that they make and grant Carnegie Mellon * the rights to redistribute these changes. */ /* Copyright 1988, 1989, 1990, 1991, 1992 by Intel Corporation, Santa Clara, California. All Rights Reserved Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appears in all copies and that both the copyright notice and this permission notice appear in supporting documentation, and that the name of Intel not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. INTEL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL INTEL BE LIABLE FOR ANY SPECIAL, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT, NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ #include <machine/asm.h> CR0_PE = 0x1 .data .globl _C_LABEL(ourseg) _C_LABEL(ourseg): .long 0 /************************************************************************** GLOBAL DESCRIPTOR TABLE **************************************************************************/ #ifdef __ELF__ .align 16 #else .align 4 #endif gdt: .word 0, 0 .byte 0, 0x00, 0x00, 0 #ifdef SUPPORT_LINUX /* additional dummy */ .word 0, 0 .byte 0, 0x00, 0x00, 0 #endif /* kernel code segment */ .globl flatcodeseg flatcodeseg = . - gdt .word 0xffff, 0 .byte 0, 0x9f, 0xcf, 0 /* kernel data segment */ .globl flatdataseg flatdataseg = . - gdt .word 0xffff, 0 .byte 0, 0x93, 0xcf, 0 /* boot code segment, base will be patched */ bootcodeseg = . - gdt .word 0xffff, 0 .byte 0, 0x9e, 0x40, 0 /* boot data segment, base will be patched */ bootdataseg = . - gdt #ifdef HEAP_BELOW_64K .word 0xffff, 0 .byte 0, 0x92, 0x00, 0 #else .word 0xffff, 0 .byte 0, 0x92, 0x4f, 0 #endif /* 16 bit real mode, base will be patched */ bootrealseg = . - gdt .word 0xffff, 0 .byte 0, 0x9e, 0x00, 0 /* limits (etc) for data segment in real mode */ bootrealdata = . - gdt .word 0xffff, 0 .byte 0, 0x92, 0x00, 0 gdtlen = . - gdt #ifdef __ELF__ .align 16 #else .align 4 #endif gdtarg: .word gdtlen-1 /* limit */ .long 0 /* addr, will be inserted */ .text ENTRY(start) .code16 # Check we are in real mode movl %cr0, %eax testl $CR0_PE, %eax jz 2f mov $1f, %si call message ret 1: .asciz "must be in real mode\r\n" 2: xorl %eax, %eax mov %cs, %ax mov %ax, %ds mov %ax, %es movl %eax, _C_LABEL(ourseg) #ifdef STACK_START add $STACK_START / 16, %ax mov %ax, %ss mov $0xfffc, %sp #endif /* fix up GDT entries for bootstrap */ #define FIXUP(gdt_index) \ movw %ax, gdt+gdt_index+2; \ movb %bl, gdt+gdt_index+4 mov %cs, %ax shll $4, %eax shldl $16, %eax, %ebx FIXUP(bootcodeseg) FIXUP(bootrealseg) FIXUP(bootdataseg) /* fix up GDT pointer */ addl $gdt, %eax movl %eax, gdtarg+2 /* change to protected mode */ calll _C_LABEL(real_to_prot) .code32 /* clear the bss */ movl $_C_LABEL(edata), %edi movl $_C_LABEL(end), %ecx subl %edi, %ecx xorb %al, %al rep stosb call _C_LABEL(doscommain) ENTRY(_rtt) call _C_LABEL(prot_to_real) .code16 ENTRY(exit16) sti movb $0x4c, %ah /* return */ int $0x21 /* * real_to_prot() * transfer from real mode to protected mode. */ ENTRY(real_to_prot) .code16 pushl %eax # guarantee that interrupt is disabled when in prot mode cli # load the gdtr lgdtl %cs:gdtarg # set the PE bit of CR0 movl %cr0, %eax orl $CR0_PE, %eax movl %eax, %cr0 # make intrasegment jump to flush the processor pipeline and # reload CS register ljmp $bootcodeseg, $xprot xprot: .code32 # we are in USE32 mode now # set up the protected mode segment registers : DS, SS, ES movl $bootdataseg, %eax mov %ax, %ds mov %ax, %es mov %ax, %ss #ifdef STACK_START addl $STACK_START, %esp #endif popl %eax ret /* * prot_to_real() * transfer from protected mode to real mode */ ENTRY(prot_to_real) .code32 pushl %eax # set up a dummy stack frame for the second seg change. # Adjust the intersegment jump instruction following # the clearing of protected mode bit. # This is self-modifying code, but we need a writable # code segment, and an intersegment return does not give us that. movl _C_LABEL(ourseg), %eax movw %ax, xreal-2 /* * Load the segment registers while still in protected mode. * Otherwise the control bits don't get changed. * The correct values are loaded later. */ movw $bootrealdata, %ax movw %ax, %ds movw %ax, %es movw %ax, %ss # Change to use16 mode. ljmp $bootrealseg, $x16 x16: .code16 # clear the PE bit of CR0 movl %cr0, %eax andl $~CR0_PE, %eax movl %eax, %cr0 # Here we have an 16 bits intersegment jump. ljmp $0, $xreal /* segment patched above */ xreal: # we are in real mode now # set up the real mode segment registers : DS, SS, ES mov %cs, %ax mov %ax, %ds mov %ax, %es #ifdef STACK_START add $STACK_START / 16, %ax mov %ax, %ss subl $STACK_START, %esp #else mov %ax, %ss #endif push %bp movw %sp, %bp /* check we are returning to an address below 64k */ movw 2/*bp*/ + 4/*eax*/ + 2(%bp), %ax /* high bits ret addr */ test %ax, %ax jne 1f pop %bp sti popl %eax retl 1: movw $2f, %si call message movl 2/*bp*/ + 4/*eax*/(%bp), %eax /* return address */ call dump_eax jmp exit16 2: .asciz "prot_to_real can't return to " /************************************************************************** ___MAIN - Dummy to keep GCC happy **************************************************************************/ ENTRY(__main) ret /* * pbzero(dst, cnt) * where dst is a physical address and cnt is the length */ ENTRY(pbzero) .code32 pushl %ebp movl %esp, %ebp pushl %es pushl %edi cld # set %es to point at the flat segment movl $flatdataseg, %eax mov %ax, %es movl 8(%ebp), %edi # destination movl 12(%ebp), %ecx # count xorl %eax, %eax # value rep stosb popl %edi popl %es popl %ebp ret /* * vpbcopy(src, dst, cnt) * where src is a virtual address and dst is a physical address */ ENTRY(vpbcopy) .code32 pushl %ebp movl %esp, %ebp pushl %es pushl %esi pushl %edi cld # set %es to point at the flat segment movl $flatdataseg, %eax mov %ax, %es movl 8(%ebp), %esi # source movl 12(%ebp), %edi # destination movl 16(%ebp), %ecx # count rep movsb popl %edi popl %esi popl %es popl %ebp ret /* * pvbcopy(src, dst, cnt) * where src is a physical address and dst is a virtual address */ ENTRY(pvbcopy) .code32 pushl %ebp movl %esp, %ebp pushl %ds pushl %esi pushl %edi cld # set %ds to point at the flat segment movl $flatdataseg, %eax mov %ax, %ds movl 8(%ebp), %esi # source movl 12(%ebp), %edi # destination movl 16(%ebp), %ecx # count rep movsb popl %edi popl %esi popl %ds popl %ebp ret ENTRY(vtophys) .code32 movl _C_LABEL(ourseg), %eax shll $4, %eax addl 4(%esp), %eax ret message: .code16 pushal message_1: cld 1: lodsb testb %al, %al jz 2f movb $0xe, %ah movw $1, %bx int $0x10 jmp 1b 2: movb $0x86, %ah mov $16, %cx int $0x15 /* delay about a second */ popal ret /* These are useful for debugging */ .data eax_buf: .long 0, 0, 0, 0 .text ENTRY(dump_eax) .code16 pushal movw $eax_buf, %si mov %si, %di movw $8, %cx 1: roll $4, %eax mov %ax, %bx andb $0x0f, %al addb $0x30, %al /* 30..3f - clear AF */ #if 1 /* 5 bytes to generate real hex... */ daa /* 30..39, 40..45 */ addb $0xc0, %al /* f0..f9, 00..05 */ adcb $0x40, %al /* 30..39, 41..45 */ #endif movb %al, (%di) /* %es != %ds, so can't ... */ inc %di /* ... use stosb */ mov %bx, %ax loop 1b movw $0x20, %ax /* space + null */ movw %ax, (%di) jmp message_1 .globl _C_LABEL(trace_word) _C_LABEL(trace_word): .code32 movl 4(%esp), %edx call _C_LABEL(prot_to_real) .code16 movl %edx, %eax call dump_eax calll _C_LABEL(real_to_prot) .code32 ret .globl _C_LABEL(trace_str) _C_LABEL(trace_str): .code32 pushl %esi call _C_LABEL(prot_to_real) .code16 mov %sp, %si mov 8(%si), %si call message calll _C_LABEL(real_to_prot) .code32 popl %esi ret
