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Diffstat (limited to 'src/cpu/i386/entry16.inc')
| -rw-r--r-- | src/cpu/i386/entry16.inc | 112 |
1 files changed, 112 insertions, 0 deletions
diff --git a/src/cpu/i386/entry16.inc b/src/cpu/i386/entry16.inc new file mode 100644 index 0000000000..c357504735 --- /dev/null +++ b/src/cpu/i386/entry16.inc @@ -0,0 +1,112 @@ +/* +This software and ancillary information (herein called SOFTWARE ) +called LinuxBIOS is made available under the terms described +here. The SOFTWARE has been approved for release with associated +LA-CC Number 00-34 . Unless otherwise indicated, this SOFTWARE has +been authored by an employee or employees of the University of +California, operator of the Los Alamos National Laboratory under +Contract No. W-7405-ENG-36 with the U.S. Department of Energy. The +U.S. Government has rights to use, reproduce, and distribute this +SOFTWARE. The public may copy, distribute, prepare derivative works +and publicly display this SOFTWARE without charge, provided that this +Notice and any statement of authorship are reproduced on all copies. +Neither the Government nor the University makes any warranty, express +or implied, or assumes any liability or responsibility for the use of +this SOFTWARE. If SOFTWARE is modified to produce derivative works, +such modified SOFTWARE should be clearly marked, so as not to confuse +it with the version available from LANL. + */ +/* Copyright 2000, Ron Minnich, Advanced Computing Lab, LANL + * rminnich@lanl.gov + */ + + +/** Start code to put an i386 or later processor into 32-bit + * protected mode. + */ + +/* .section ".rom.text" */ +#include <arch/rom_segs.h> +.code16 +.globl EXT(_start) +.type EXT(_start), @function + +EXT(_start): + cli + +/* thanks to kmliu@sis.tw.com for this TBL fix ... */ +/**/ +/* IMMEDIATELY invalidate the translation lookaside buffer before executing*/ +/* any further code. Even though paging is disabled we could still get*/ +/*false address translations due to the TLB if we didn't invalidate it.*/ +/**/ + xorl %eax, %eax + movl %eax, %cr3 /* Invalidate TLB*/ + + /* invalidate the cache */ + invd + + /* Note: gas handles memory addresses in 16 bit code very poorly. + * In particular it doesn't appear to have a directive allowing you + * associate a section or even an absolute offset with a segment register. + * + * This means that anything except cs:ip relative offsets are + * a real pain in 16 bit mode. And explains why it is almost + * imposible to get gas to do lgdt correctly. + * + * One way to work around this is to have the linker do the + * math instead of the assembler. This solves the very + * pratical problem of being able to write code that can + * be relocated. + * + * An lgdt call before we have memory enabled cannot be + * position independent, as we cannot execute a call + * instruction to get our current instruction pointer. + * So while this code is relocateable it isn't arbitrarily + * relocatable. + * + * The criteria for relocation have been relaxed to their + * utmost, so that we can use the same code for both + * our initial entry point and startup of the second cpu. + * The code assumes when executing at _start that: + * (((cs & 0xfff) == 0) and (ip == _start & 0xffff)) + * or + * ((cs == anything) and (ip == 0)). + * + * The restrictions in reset16.inc mean that _start initially + * must be loaded at or above 0xffff0000 or below 0x100000. + * + * The linker scripts computs gdtptr16_offset by simply returning + * the low 16 bits. This means that the intial segment used + * when start is called must be 64K aligned. This should not + * restrict the address as the ip address can be anything. + */ + + movw %cs, %ax + shlw $4, %ax + movw $EXT(gdtptr16_offset), %bx + subw %ax, %bx + data32 lgdt %cs:(%bx) + + movl %cr0, %eax + andl $0x7FFAFFD1, %eax /* PG,AM,WP,NE,TS,EM,MP = 0 */ + orl $0x60000001, %eax /* CD, NW, PE = 1 */ + movl %eax, %cr0 + + /* Now that we are in protected mode jump to a 32 bit code segment. */ + data32 ljmp $ROM_CODE_SEG, $__protected_start + +/** The gdt has a 4 Gb code segment at 0x10, and a 4 GB data segment + * at 0x18; these are Linux-compatible. + */ + +.align 4 +.globl EXT(gdtptr16) +EXT(gdtptr16): + .word gdt_end - gdt -1 /* compute the table limit */ + .long gdt /* we know the offset */ + +.globl EXT(_estart) +EXT(_estart): + .code32 + |