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Diffstat (limited to 'stand/i386/boot2/boot1.S')
| -rw-r--r-- | stand/i386/boot2/boot1.S | 373 |
1 files changed, 373 insertions, 0 deletions
diff --git a/stand/i386/boot2/boot1.S b/stand/i386/boot2/boot1.S new file mode 100644 index 0000000..984ab52 --- /dev/null +++ b/stand/i386/boot2/boot1.S @@ -0,0 +1,373 @@ +/* + * 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,0x8c00 # 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. Note that boot1 does not use this relocated copy + * of itself while loading boot2; however, BTX reclaims the memory + * used by boot1 during its initialization. As a result, boot2 uses + * xread from the relocated copy. + */ + 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 0x8c00 as our transfer buffer. Thus, + * boot1 ends up at 0x8c00, and boot2 starts at 0x8c00 + 0x200 = 0x8e00. + * The first part of boot2 is the disklabel, which is 0x200 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 + +/* + * Enable A20 so we can access memory above 1 meg. + * Use the zero-valued %cx as a timeout for embedded hardware which do not + * have a keyboard controller. + */ +seta20: cli # Disable interrupts +seta20.1: dec %cx # Timeout? + jz seta20.3 # Yes + 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 +seta20.3: sti # Enable interrupts + + jmp start+MEM_JMP-MEM_ORG # Start BTX + + +/* + * 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 $0xf000,$0xfff0 # 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: testb $FL_PACKET,%cs:MEM_REL+flags-start # LBA support enabled? + jz read.1 # No, use CHS + cmpb $0x80,%dl # Hard drive? + jb read.1 # No, use CHS + mov $0x55aa,%bx # Magic + push %dx # Save + movb $0x41,%ah # BIOS: Check + int $0x13 # extensions present + pop %dx # Restore + jc read.1 # If error, use CHS + cmp $0xaa55,%bx # Magic? + jne read.1 # No, so use CHS + testb $0x1,%cl # Packet interface? + jz read.1 # No, so use CHS + mov %bp,%si # Disk packet + movb $0x42,%ah # BIOS: Extended + int $0x13 # read + retw # To caller +read.1: 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 ereturn # No, return an error + 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.1 # If not done +read.6: 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 |
