/*
 * Copyright (c) 2000 John Baldwin
 * 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: src/sys/boot/i386/pxeldr/pxeldr.s,v 1.9 2003/09/03 08:12:20 phk Exp $
 * $DragonFly: src/sys/boot/pc32/pxeldr/pxeldr.S,v 1.5 2007/05/18 07:41:43 dillon Exp $
 */

/*
 * This simple program is a preloader for the normal boot3 loader.  It is
 * simply prepended to the beginning of a fully built and btxld'd loader.
 * It then copies the loader to the address boot2 normally loads it,
 * emulates the boot[12] environment (protected mode, a bootinfo struct,
 * etc.), and then jumps to the start of btxldr to start the boot process.
 * This method allows a stock /boot/loader to be booted over the network
 * via PXE w/o having to write a separate PXE-aware client just to load
 * the loader.
 */
#include "../bootasm.h"

                /*
                 * a.out header fields
                 */
                .set AOUT_TEXT,0x04             # text segment size
                .set AOUT_DATA,0x08             # data segment size
                .set AOUT_BSS,0x0c              # zerod BSS size
                .set AOUT_SYMBOLS,0x10          # symbol table
                .set AOUT_ENTRY,0x14            # entry point
                .set AOUT_HEADER,MEM_PAGE_SIZE  # size of the a.out header

                /*
                 * Flags for kargs->bootflags
                 */
                .set KARGS_FLAGS_PXE,0x2        # flag to indicate booting from
                                                #  PXE loader
                /*
                 * Boot howto bits
                 */
                .set RB_SERIAL,0x1000           # serial console

                /*
                 * Segment selectors.
                 */
                .set SEL_SDATA,0x8              # Supervisor data
                .set SEL_RDATA,0x10             # Real mode data
                .set SEL_SCODE,0x18             # PM-32 code
                .set SEL_SCODE16,0x20           # PM-16 code

                /*
                 * BTX constants
                 */
                .set INT_SYS,0x30               # BTX syscall interrupt

                /*
                 * Bit in BDA_KEYBOARD that is set if an enhanced
                 * keyboard is present.
                 */
                .set KEYBOARD_BIT,0x10

                /*
                 * We expect to be loaded by the BIOS at LOAD (0x7c00),
                 * which is the standard boot loader entry point.
                 */
                .code16
                .globl start
                .org 0x0, 0x0

                /*
                 * BTX program loader for PXE network booting
                 */
start:          cld                             # string ops inc
                xorw %ax, %ax                   # zero %ax
                movw %ax, %ss                   # setup the
                movw $start, %sp                #  stack
                movw %es, %cx                   # save PXENV+ segment
                movw %ax, %ds                   # setup the
                movw %ax, %es                   #  data segments
                andl $0xffff, %ecx              # clear upper words
                andl $0xffff, %ebx              #  of %ebx and %ecx
                shll $4, %ecx                   # calculate the offset of
                addl %ebx, %ecx                 #  the PXENV+ struct and
                pushl %ecx                      #  save it on the stack
                movw $welcome_msg, %si          # %ds:(%si) -> welcome message
                callw putstr                    # display the welcome message

                /*
                 * Setup the arguments that the loader is expecting
                 * from boot[12]
                 */
                movw $bootinfo_msg, %si         # %ds:(%si) -> boot args message
                callw putstr                    # display the message
                movw $MEM_ARG, %bx              # %ds:(%bx) -> boot args
                movw %bx, %di                   # %es:(%di) -> boot args
                xorl %eax, %eax                 # zero %eax
                movw $(MEM_ARG_SIZE/4), %cx     # Size of arguments in 32-bit
                                                #  dwords
                rep                             # Clear the arguments
                stosl                           #  to zero
                orb $KARGS_FLAGS_PXE, 0x8(%bx)  # kargs->bootflags |=
                                                #  KARGS_FLAGS_PXE
                popl 0xc(%bx)                   # kargs->pxeinfo = *PXENV+
#ifdef ALWAYS_SERIAL
                /*
                 * set the RBX_SERIAL bit in the howto byte.
                 */
                orl $RB_SERIAL, (%bx)           # enable serial console
#endif
#ifdef PROBE_KEYBOARD
                /*
                 * Look at the BIOS data area to see if we have an enhanced
                 * keyboard.  If not, set the RBX_SERIAL bit in the howto 
                 * byte.
                 */
                testb $KEYBOARD_BIT, BDA_KEYBOARD # keyboard present?
                jnz keyb                        # yes, so skip
                orl $RB_SERIAL, (%bx)           # enable serial console
keyb:
#endif
                /*
                 * Turn on the A20 address line
                 */
                callw seta20                    # Turn A20 on

                /*
                 * Relocate the loader and BTX using a very lazy protected
                 * mode
                 */
                movw $relocate_msg, %si         # Display the
                callw putstr                    #  relocation message
                movl end+AOUT_ENTRY, %edi       # %edi is the destination
                movl $(end+AOUT_HEADER), %esi   # %esi is
                                                #  the start of the text
                                                #  segment
                movl end+AOUT_TEXT, %ecx        # %ecx = length of the text
                                                #  segment
                lgdt gdtdesc                    # setup our own gdt
                cli                             # turn off interrupts
                movl %cr0, %eax                 # Turn on
                orb $0x1, %al                   #  protected
                movl %eax, %cr0                 #  mode
                ljmp $SEL_SCODE,$pm_start       # long jump to clear the
                                                #  instruction pre-fetch queue
                .code32
pm_start:       movw $SEL_SDATA, %ax            # Initialize
                movw %ax, %ds                   #  %ds and
                movw %ax, %es                   #  %es to a flat selector
                rep                             # Relocate the
                movsb                           #  text segment
                addl $(MEM_PAGE_SIZE - 1), %edi # pad %edi out to a new page
                andl $~(MEM_PAGE_SIZE - 1), %edi #  for the data segment
                movl end+AOUT_DATA, %ecx        # size of the data segment
                rep                             # Relocate the
                movsb                           #  data segment
                movl end+AOUT_BSS, %ecx         # size of the bss
                xorl %eax, %eax                 # zero %eax
                addb $3, %cl                    # round %ecx up to
                shrl $2, %ecx                   #  a multiple of 4
                rep                             # zero the
                stosl                           #  bss
                movl end+AOUT_ENTRY, %esi       # %esi -> relocated loader
                addl $MEM_BTX_LDR_OFF, %esi     # %esi -> BTX in the loader
                movl $MEM_BTX_ORG, %edi # %edi -> where BTX needs to go
                movzwl 0xa(%esi), %ecx          # %ecx -> length of BTX
                rep                             # Relocate
                movsb                           #  BTX
                ljmp $SEL_SCODE16,$pm_16        # Jump to 16-bit PM
                .code16
pm_16:          movw $SEL_RDATA, %ax            # Initialize
                movw %ax, %ds                   #  %ds and
                movw %ax, %es                   #  %es to a real mode selector
                movl %cr0, %eax                 # Turn off
                andb $~0x1, %al                 #  protected
                movl %eax, %cr0                 #  mode
                ljmp $0,$pm_end                 # Long jump to clear the
                                                #  instruction pre-fetch queue
pm_end:         sti                             # Turn interrupts back on now

                /*
                 * Copy the BTX client to MEM_BTX_USR
                 */
                xorw %ax, %ax                   # zero %ax and set
                movw %ax, %ds                   #  %ds and %es
                movw %ax, %es                   #  to segment 0
                movw $MEM_BTX_USR, %di          # Prepare to relocate
                movw $btx_client, %si           #  the simple btx client
                movw $(btx_client_end-btx_client), %cx # length of btx client
                rep                             # Relocate the
                movsb                           #  simple BTX client

                /*
                 * Copy the boot[12] args to where the BTX client can
                 * see them
                 */
                movw $MEM_ARG, %si              # where the args are at now
                movw $MEM_BTX_USR_ARG, %di              # where the args are moving to
                movw $(MEM_ARG_SIZE/4), %cx     # size of the arguments in longs
                rep                             # Relocate
                movsl                           #  the words

                /*
                 * Save the entry point so the client can get to it later on
                 */
                movl end+AOUT_ENTRY, %eax       # load the entry point
                stosl                           # add it to the end of the
                                                #  arguments
                /*
                 * Now we just start up BTX and let it do the rest
                 */
                movw $jump_message, %si         # Display the
                callw putstr                    #  jump message
                ljmp $0,$MEM_BTX_ENTRY          # Jump to the BTX entry point

                /*
                 * Display a null-terminated string
                 */
putstr:         lodsb                           # load %al from %ds:(%si)
                testb %al,%al                   # stop at null
                jnz putc                        # if the char != null, output it
                retw                            # return when null is hit
putc:           movw $0x7,%bx                   # attribute for output
                movb $0xe,%ah                   # BIOS: put_char
                int $0x10                       # call BIOS, print char in %al
                jmp putstr                      # keep looping

                /*
                 * Enable A20. Put upper limit on amount of time we wait for the
                 * keyboard controller to get ready (65K x ISA access time). If
                 * we wait more than that amount it's likely that the hardware
                 * is legacy-free and simply doesn't have keyboard controller
                 * and don't need enabling A20 at all.
                 */
seta20:         cli                             # Disable interrupts
                xor %cx,%cx                     # Clear
seta20.1:       inc %cx                         # Increment, overflow?
                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
                retw                            # To caller

                /*
                 * BTX client to start btxldr
                 */
                .code32
btx_client:     movl $(MEM_BTX_USR_ARG-MEM_BTX_USR+MEM_ARG_SIZE-4), %esi
                                                # %ds:(%esi) -> end
                                                #  of boot[12] args
                movl $(MEM_ARG_SIZE/4), %ecx    # Number of words to push
                std                             # Go backwards
push_arg:       lodsl                           # Read argument
                pushl %eax                      # Push it onto the stack
                loop push_arg                   # Push all of the arguments
                cld                             # In case anyone depends on this
                pushl MEM_BTX_USR_ARG-MEM_BTX_USR+MEM_ARG_SIZE # Entry point of
                                                #  the loader
                pushl %eax                      # Emulate a near call
                movl $0x1, %eax                 # "exec" system call
                int $INT_SYS                    # BTX system call
btx_client_end:
                .code16

                .p2align 4

                /*
                 * Global descriptor table.
                 */
gdt:            .word 0x0,0x0,0x0,0x0           # Null entry
                .word 0xffff,0x0,0x9200,0xcf    # SEL_SDATA
                .word 0xffff,0x0,0x9200,0x0     # SEL_RDATA
                .word 0xffff,0x0,0x9a00,0xcf    # SEL_SCODE (32-bit)
                .word 0xffff,0x0,0x9a00,0x8f    # SEL_SCODE16 (16-bit)
gdt.1:

                /*
                 * Pseudo-descriptors.
                 */
gdtdesc:        .word gdt.1-gdt-1               # Limit
                .long gdt                       # Base

welcome_msg:    .asciz  "PXE Loader 1.00\r\n\n"
bootinfo_msg:   .asciz  "Building the boot loader arguments\r\n"
relocate_msg:   .asciz  "Relocating the loader and the BTX\r\n"
jump_message:   .asciz  "Starting the BTX loader\r\n"

                .p2align 4
end: