9778b7b790
git-svn-id: http://svn.lfbs.rwth-aachen.de/svn/scc/trunk/MetalSVM@2 315a16e6-25f9-4109-90ae-ca3045a26c18
99 lines
2.8 KiB
C
99 lines
2.8 KiB
C
/*
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* Copyright 2010 Stefan Lankes, Chair for Operating Systems,
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* RWTH Aachen University
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* This file is part of MetalSVM.
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*/
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#include <metalsvm/string.h>
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/* Defines a GDT entry */
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struct gdt_entry {
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unsigned short limit_low;
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unsigned short base_low;
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unsigned char base_middle;
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unsigned char access;
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unsigned char granularity;
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unsigned char base_high;
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} __attribute__ ((packed));
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struct gdt_ptr {
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unsigned short limit;
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unsigned int base;
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} __attribute__ ((packed));
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#define GDT_ENTRIES 3
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struct gdt_entry gdt[GDT_ENTRIES];
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struct gdt_ptr gp;
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/*
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* This is in start.asm. We use this to properly reload
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* the new segment registers
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*/
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extern void gdt_flush(void);
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/* Setup a descriptor in the Global Descriptor Table */
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static void gdt_set_gate(int num, unsigned long base, unsigned long limit,
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unsigned char access, unsigned char gran)
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{
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/* Setup the descriptor base address */
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gdt[num].base_low = (base & 0xFFFF);
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gdt[num].base_middle = (base >> 16) & 0xFF;
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gdt[num].base_high = (base >> 24) & 0xFF;
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/* Setup the descriptor limits */
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gdt[num].limit_low = (limit & 0xFFFF);
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gdt[num].granularity = ((limit >> 16) & 0x0F);
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/* Finally, set up the granularity and access flags */
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gdt[num].granularity |= (gran & 0xF0);
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gdt[num].access = access;
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}
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/*
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* This will setup the special GDT
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* pointer, set up the entries in our GDT, and then
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* finally call gdt_flush() in our assembler file in order
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* to tell the processor where the new GDT is and update the
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* new segment registers
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*/
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void gdt_install(void)
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{
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/* Setup the GDT pointer and limit */
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gp.limit = (sizeof(struct gdt_entry) * GDT_ENTRIES) - 1;
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gp.base = (unsigned int) &gdt;
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/* Our NULL descriptor */
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gdt_set_gate(0, 0, 0, 0, 0);
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/*
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* The second entry is our Code Segment. The base address
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* is 0, the limit is 4 GByte, it uses 4KByte granularity,
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* uses 32-bit opcodes, and is a Code Segment descriptor.
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*/
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gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
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/*
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* The third entry is our Data Segment. It's EXACTLY the
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* same as our code segment, but the descriptor type in
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* this entry's access byte says it's a Data Segment
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*/
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gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
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/* Flush out the old GDT and install the new changes! */
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gdt_flush();
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}
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