diff options
Diffstat (limited to 'sys/boot/i386/boot2/boot1.S')
| -rw-r--r-- | sys/boot/i386/boot2/boot1.S | 365 |
1 files changed, 365 insertions, 0 deletions
diff --git a/sys/boot/i386/boot2/boot1.S b/sys/boot/i386/boot2/boot1.S new file mode 100644 index 0000000..f7d9df6 --- /dev/null +++ b/sys/boot/i386/boot2/boot1.S @@ -0,0 +1,365 @@ +// +// Copyright (c) 1998 Robert Nordier +// All rights reserved. +// +// Redistribution and use in source and binary forms are freely +// permitted provided that the above copyright notice and this +// paragraph and the following disclaimer are duplicated in all +// such forms. +// +// This software is provided "AS IS" and without any express or +// implied warranties, including, without limitation, the implied +// warranties of merchantability and fitness for a particular +// purpose. +// + +// $FreeBSD$ + +// Memory Locations + .set MEM_REL,0x700 // Relocation address + .set MEM_ARG,0x900 // Arguments + .set MEM_ORG,0x7c00 // Origin + .set MEM_BUF,0x8cec // Load area + .set MEM_BTX,0x9000 // BTX start + .set MEM_JMP,0x9010 // BTX entry point + .set MEM_USR,0xa000 // Client start + .set BDA_BOOT,0x472 // Boot howto flag + +// Partition Constants + .set PRT_OFF,0x1be // Partition offset + .set PRT_NUM,0x4 // Partitions + .set PRT_BSD,0xa5 // Partition type + +// Flag Bits + .set FL_PACKET,0x80 // Packet mode + +// Misc. Constants + .set SIZ_PAG,0x1000 // Page size + .set SIZ_SEC,0x200 // Sector size + + .set NSECT,0x10 + .globl start + .globl xread + .code16 + +start: jmp main // Start recognizably + +// This is the start of a standard BIOS Parameter Block (BPB). Most bootable +// FAT disks have this at the start of their MBR. While normal BIOS's will +// work fine without this section, IBM's El Torito emulation "fixes" up the +// BPB by writing into the memory copy of the MBR. Rather than have data +// written into our xread routine, we'll define a BPB to work around it. +// The data marked with (T) indicates a field required for a ThinkPad to +// recognize the disk and (W) indicates fields written from IBM BIOS code. +// The use of the BPB is based on what OpenBSD and NetBSD implemented in +// their boot code but the required fields were determined by trial and error. +// +// Note: If additional space is needed in boot1, one solution would be to +// move the "prompt" message data (below) to replace the OEM ID. + + .org 0x03, 0x00 +oemid: .space 0x08, 0x00 // OEM ID + + .org 0x0b, 0x00 +bpb: .word 512 // sector size (T) + .byte 0 // sectors/clustor + .word 0 // reserved sectors + .byte 0 // number of FATs + .word 0 // root entries + .word 0 // small sectors + .byte 0 // media type (W) + .word 0 // sectors/fat + .word 18 // sectors per track (T) + .word 2 // number of heads (T) + .long 0 // hidden sectors (W) + .long 0 // large sectors + + .org 0x24, 0x00 +ebpb: .byte 0 // BIOS physical drive number (W) + + .org 0x25,0x90 +// +// Trampoline used by boot2 to call read to read data from the disk via +// the BIOS. Call with: +// +// %cx:%ax - long - LBA to read in +// %es:(%bx) - caddr_t - buffer to read data into +// %dl - byte - drive to read from +// %dh - byte - num sectors to read +// + +xread: push %ss // Address + pop %ds // data +// +// Setup an EDD disk packet and pass it to read +// +xread.1: // Starting + pushl $0x0 // absolute + push %cx // block + push %ax // number + push %es // Address of + push %bx // transfer buffer + xor %ax,%ax // Number of + movb %dh,%al // blocks to + push %ax // transfer + push $0x10 // Size of packet + mov %sp,%bp // Packet pointer + callw read // Read from disk + lea 0x10(%bp),%sp // Clear stack + lret // To far caller +// +// Load the rest of boot2 and BTX up, copy the parts to the right locations, +// and start it all up. +// + +// +// Setup the segment registers to flat addressing (segment 0) and setup the +// stack to end just below the start of our code. +// +main: cld // String ops inc + xor %cx,%cx // Zero + mov %cx,%es // Address + mov %cx,%ds // data + mov %cx,%ss // Set up + mov $start,%sp // stack +// +// Relocate ourself to MEM_REL. Since %cx == 0, the inc %ch sets +// %cx == 0x100. +// + mov %sp,%si // Source + mov $MEM_REL,%di // Destination + incb %ch // Word count + rep // Copy + movsw // code +// +// If we are on a hard drive, then load the MBR and look for the first +// FreeBSD slice. We use the fake partition entry below that points to +// the MBR when we call nread. The first pass looks for the first active +// FreeBSD slice. The second pass looks for the first non-active FreeBSD +// slice if the first one fails. +// + mov $part4,%si // Partition + cmpb $0x80,%dl // Hard drive? + jb main.4 // No + movb $0x1,%dh // Block count + callw nread // Read MBR + mov $0x1,%cx // Two passes +main.1: mov $MEM_BUF+PRT_OFF,%si // Partition table + movb $0x1,%dh // Partition +main.2: cmpb $PRT_BSD,0x4(%si) // Our partition type? + jne main.3 // No + jcxz main.5 // If second pass + testb $0x80,(%si) // Active? + jnz main.5 // Yes +main.3: add $0x10,%si // Next entry + incb %dh // Partition + cmpb $0x1+PRT_NUM,%dh // In table? + jb main.2 // Yes + dec %cx // Do two + jcxz main.1 // passes +// +// If we get here, we didn't find any FreeBSD slices at all, so print an +// error message and die. +// + mov $msg_part,%si // Message + jmp error // Error +// +// Floppies use partition 0 of drive 0. +// +main.4: xor %dx,%dx // Partition:drive +// +// Ok, we have a slice and drive in %dx now, so use that to locate and load +// boot2. %si references the start of the slice we are looking for, so go +// ahead and load up the first 16 sectors (boot1 + boot2) from that. When +// we read it in, we conveniently use 0x8cec as our transfer buffer. Thus, +// boot1 ends up at 0x8cec, and boot2 starts at 0x8cec + 0x200 = 0x8eec. +// The first part of boot2 is the disklabel, which is 0x114 bytes long. +// The second part is BTX, which is thus loaded into 0x9000, which is where +// it also runs from. The boot2.bin binary starts right after the end of +// BTX, so we have to figure out where the start of it is and then move the +// binary to 0xc000. Normally, BTX clients start at MEM_USR, or 0xa000, but +// when we use btxld to create boot2, we use an entry point of 0x2000. That +// entry point is relative to MEM_USR; thus boot2.bin starts at 0xc000. +// +main.5: mov %dx,MEM_ARG // Save args + movb $NSECT,%dh // Sector count + callw nread // Read disk + mov $MEM_BTX,%bx // BTX + mov 0xa(%bx),%si // Get BTX length and set + add %bx,%si // %si to start of boot2.bin + mov $MEM_USR+SIZ_PAG*2,%di // Client page 2 + mov $MEM_BTX+(NSECT-1)*SIZ_SEC,%cx // Byte + sub %si,%cx // count + rep // Relocate + movsb // client + sub %di,%cx // Byte count + xorb %al,%al // Zero assumed bss from + rep // the end of boot2.bin + stosb // up to 0x10000 + callw seta20 // Enable A20 + jmp start+MEM_JMP-MEM_ORG // Start BTX +// +// Enable A20 so we can access memory above 1 meg. +// +seta20: cli // Disable interrupts +seta20.1: inb $0x64,%al // Get status + testb $0x2,%al // Busy? + jnz seta20.1 // Yes + movb $0xd1,%al // Command: Write + outb %al,$0x64 // output port +seta20.2: inb $0x64,%al // Get status + testb $0x2,%al // Busy? + jnz seta20.2 // Yes + movb $0xdf,%al // Enable + outb %al,$0x60 // A20 + sti // Enable interrupts + retw // To caller +// +// Trampoline used to call read from within boot1. +// +nread: mov $MEM_BUF,%bx // Transfer buffer + mov 0x8(%si),%ax // Get + mov 0xa(%si),%cx // LBA + push %cs // Read from + callw xread.1 // disk + jnc return // If success, return + mov $msg_read,%si // Otherwise, set the error + // message and fall through to + // the error routine +// +// Print out the error message pointed to by %ds:(%si) followed +// by a prompt, wait for a keypress, and then reboot the machine. +// +error: callw putstr // Display message + mov $prompt,%si // Display + callw putstr // prompt + xorb %ah,%ah // BIOS: Get + int $0x16 // keypress + movw $0x1234, BDA_BOOT // Do a warm boot + ljmp $0xffff,$0x0 // reboot the machine +// +// Display a null-terminated string using the BIOS output. +// +putstr.0: mov $0x7,%bx // Page:attribute + movb $0xe,%ah // BIOS: Display + int $0x10 // character +putstr: lodsb // Get char + testb %al,%al // End of string? + jne putstr.0 // No + +// +// Overused return code. ereturn is used to return an error from the +// read function. Since we assume putstr succeeds, we (ab)use the +// same code when we return from putstr. +// +ereturn: movb $0x1,%ah // Invalid + stc // argument +return: retw // To caller +// +// Reads sectors from the disk. If EDD is enabled, then check if it is +// installed and use it if it is. If it is not installed or not enabled, then +// fall back to using CHS. Since we use a LBA, if we are using CHS, we have to +// fetch the drive parameters from the BIOS and divide it out ourselves. +// Call with: +// +// %dl - byte - drive number +// stack - 10 bytes - EDD Packet +// +read: push %dx // Save + movb $0x8,%ah // BIOS: Get drive + int $0x13 // parameters + movb %dh,%ch // Max head number + pop %dx // Restore + jc return // If error + andb $0x3f,%cl // Sectors per track + jz ereturn // If zero + cli // Disable interrupts + mov 0x8(%bp),%eax // Get LBA + push %dx // Save + movzbl %cl,%ebx // Divide by + xor %edx,%edx // sectors + div %ebx // per track + movb %ch,%bl // Max head number + movb %dl,%ch // Sector number + inc %bx // Divide by + xorb %dl,%dl // number + div %ebx // of heads + movb %dl,%bh // Head number + pop %dx // Restore + cmpl $0x3ff,%eax // Cylinder number supportable? + sti // Enable interrupts + ja read.7 // No, try EDD + xchgb %al,%ah // Set up cylinder + rorb $0x2,%al // number + orb %ch,%al // Merge + inc %ax // sector + xchg %ax,%cx // number + movb %bh,%dh // Head number + subb %ah,%al // Sectors this track + mov 0x2(%bp),%ah // Blocks to read + cmpb %ah,%al // To read + jb read.2 // this +#ifdef TRACK_AT_A_TIME + movb %ah,%al // track +#else + movb $1,%al // one sector +#endif +read.2: mov $0x5,%di // Try count +read.3: les 0x4(%bp),%bx // Transfer buffer + push %ax // Save + movb $0x2,%ah // BIOS: Read + int $0x13 // from disk + pop %bx // Restore + jnc read.4 // If success + dec %di // Retry? + jz read.6 // No + xorb %ah,%ah // BIOS: Reset + int $0x13 // disk system + xchg %bx,%ax // Block count + jmp read.3 // Continue +read.4: movzbw %bl,%ax // Sectors read + add %ax,0x8(%bp) // Adjust + jnc read.5 // LBA, + incw 0xa(%bp) // transfer +read.5: shlb %bl // buffer + add %bl,0x5(%bp) // pointer, + sub %al,0x2(%bp) // block count + ja read // If not done +read.6: retw // To caller +read.7: testb $FL_PACKET,%cs:MEM_REL+flags-start // LBA support enabled? + jz ereturn // No, so return an error + mov $0x55aa,%bx // Magic + push %dx // Save + movb $0x41,%ah // BIOS: Check + int $0x13 // extensions present + pop %dx // Restore + jc return // If error, return an error + cmp $0xaa55,%bx // Magic? + jne ereturn // No, so return an error + testb $0x1,%cl // Packet interface? + jz ereturn // No, so return an error + mov %bp,%si // Disk packet + movb $0x42,%ah // BIOS: Extended + int $0x13 // read + retw // To caller + +// Messages + +msg_read: .asciz "Read" +msg_part: .asciz "Boot" + +prompt: .asciz " error\r\n" + +flags: .byte FLAGS // Flags + + .org PRT_OFF,0x90 + +// Partition table + + .fill 0x30,0x1,0x0 +part4: .byte 0x80, 0x00, 0x01, 0x00 + .byte 0xa5, 0xfe, 0xff, 0xff + .byte 0x00, 0x00, 0x00, 0x00 + .byte 0x50, 0xc3, 0x00, 0x00 // 50000 sectors long, bleh + + .word 0xaa55 // Magic number |
