/* $OpenBSD: srt0.S,v 1.4 2022/12/08 01:25:45 guenther Exp $ */ /* * Copyright (c) 1997 Michael Shalayeff * All rights reserved. * * 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 AUTHOR ``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 REGENTS 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. * */ #include <machine/asm.h> #include <assym.h> #define BOOTSTACK 0xfffc .globl end .globl edata .globl boot .globl _rtt .globl bios_bootdev .globl pmm_init .globl Gdtr .text .code16 .globl _start _start: #ifdef DEBUG movl $0xb80a0, %ebx addr32 movl $0x07420742, (%ebx) #endif /* Clobbers %ax, maybe more */ #define putc(c) movb $c, %al; call Lchr /* * We operate as a no emulation boot image, as defined by the * El Torito Bootable CD-ROM Format Specification v1.0. We use * a load segment of 0x07C0 (physical load address of 0x7C00). * Like the standard /boot, we are linked to run at 0x40120 * (load address 0x40000), so we relocate to there. * * From 0x7C00 to 0x40000 is 0x38400 (230400) bytes, so we don't * have to worry about an overlapping copy until cdboot is * over 225 KB. * * Our cdbr CD-ROM boot sector passes us the drive number to use * in %dl. */ #define CDBOOTADDR 0x7c00 /* Address where BIOS loads up */ xorw %ax, %ax movw %ax, %ss /* CPU disables interrupts till... */ movl $CDBOOTADDR-4, %esp /* after this instruction */ pushl %edx /* Preserve the drive number. */ movw $(CDBOOTADDR >> 4), %ax /* Reloc from %ds = 0x7c0. */ movw $(LINKADDR >> 4), %bx /* Reloc to %es = 0x4012. */ movl $end, %edx subl $_start, %edx /* How big are we? */ /* * Relocate in blocks that are a maximum of 32KB in size, incrementing * the segment registers after each block. The 'rep; movsb' instruction * uses %cx, which limits us to a maximum block size of 0xfff0, even * though we can address the full 64KB within a single segment. */ #define RELOC_BLOCK_SIZE 0x8000 reloc_loop: movl %edx, %ecx jcxz reloc_done cmpl $RELOC_BLOCK_SIZE, %ecx jbe reloc_notrunc movl $RELOC_BLOCK_SIZE, %ecx reloc_notrunc: subl %ecx, %edx movw %ax, %ds /* Where we're coming from */ xorw %si, %si movw %bx, %es /* Where we're going to */ xorw %di, %di cld rep; movsb /* Copy into place */ addw $(RELOC_BLOCK_SIZE >> 4), %ax addw $(RELOC_BLOCK_SIZE >> 4), %bx jmp reloc_loop reloc_done: popl %edx jmpl $(LINKADDR >> 4), $(relocated-_start) /* Now relocate */ relocated: /* * In 16-bit mode, we have segment registers == 0x4012, and * offsets work from here, with offset(_start) == 0. * * In 32-bit mode, we have a flat memory model, where * offset(_start) == 0x40120. This is how we're linked. * * Now transition to protected mode. * * First, initialise the global descriptor table. */ cli push %cs pop %ds addr32 data32 lgdt (Gdtr - LINKADDR) movl %cr0, %eax orl $CR0_PE, %eax data32 movl %eax, %cr0 data32 ljmp $8, $1f /* Seg sel 0x08 is flat 32-bit code */ 1: .code32 movl $0x10, %eax /* Seg sel 0x10 is flat 32-bit data */ mov %ax, %ds mov %ax, %es mov %ax, %fs mov %ax, %gs mov %ax, %ss movl $BOOTSTACK, %esp #ifdef DEBUG movl $0xb8000, %ebx movl $0x07420742, (%ebx) #endif movzbl %dl, %eax orl $0x100, %eax /* Indicate that it's a cd device */ pushl %eax /* boot() takes this as a parameter */ #ifdef DEBUG movl $0xb80a4, %ebx movl $0x07520752, (%ebx) #endif /* Zero .bss */ xorl %eax, %eax movl $end, %ecx subl $edata, %ecx movl $edata, %edi cld rep; stosb /* Set up an interrupt descriptor table for protected mode. */ call pmm_init /* Set our program name ("CDBOOT", not "BOOT"). */ movl $cd_progname, %eax movl %eax, progname /* Put the boot device number into the globals that need it */ popl %eax /* Get this back from the stack */ pushl %eax /* boot() takes this as a parameter */ movl %eax, bios_bootdev movl %eax, bios_cddev /* * Now call "main()". * * We run in flat 32-bit protected mode, with no address mapping. */ #ifdef DEBUG movl $0xb8004, %ebx movl $0x07410741, (%ebx) #endif call boot /* boot() should not return. If it does, reset computer. */ jmp _rtt ENTRY(debugchar) pushl %ebx movl 8(%esp), %ebx addl %ebx, %ebx addl $0xb8000, %ebx xorl %eax, %eax movb 12(%esp), %al andl $0xfffffffe, %ebx movb %al, (%ebx) popl %ebx ret .code16 /* * Display ASCIZ string at %si. Trashes %si. */ Lstr: pushw %ax cld 1: lodsb /* %al = *%si++ */ testb %al, %al jz 1f call Lchr jmp 1b 1: popw %ax ret /* * Write out value in %ax in hex */ hex_word: pushw %ax mov %ah, %al call hex_byte popw %ax /* fall thru */ /* * Write out value in %al in hex */ hex_byte: pushw %ax shrb $4, %al call hex_nibble popw %ax /* fall thru */ /* Write out nibble in %al */ hex_nibble: and $0x0F, %al add $'0', %al cmpb $'9', %al jbe Lchr addb $'A'-'9'-1, %al /* fall thru to Lchr */ /* * Lchr: write the character in %al to console */ Lchr: pushw %bx movb $0x0e, %ah xorw %bx, %bx incw %bx /* movw $0x01, %bx */ int $0x10 popw %bx ret cd_progname: .asciz "CDBOOT" .end
