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gdt.cpp
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gdt.cpp
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/*
* Copyright (c) 2012 Marco Hinz
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* - Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
* - Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* - Neither the name of the author nor the names of its contributors may be
* used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <stdint.h>
#include "gdt.hpp"
#include <stddef.h>
/*
* Failing setting up at least the following five entries will lead
* to a state of considerable discontent:
*
* - null entry
* - kernel code segment
* - kernel data segment
* - user code segment
* - user data segment
*/
static gdt_t gdt;
static gdt_entry_t gdt_entries[3];
void set_entry(uint8_t num, uint64_t base, uint64_t limit, uint8_t access, uint8_t gran)
{
gdt_entries[num].base_low = (base & 0xffff);
gdt_entries[num].base_middle = (base >> 16) & 0xff;
gdt_entries[num].base_high = (base >> 24) & 0xff;
gdt_entries[num].limit_low = (limit & 0xffff);
gdt_entries[num].granularity = (limit >> 16) & 0x0f;
/*
* gdt_entries[num].granularity |= (gran & 0xf0);
* Shut up, gcc -Wconversion.
*/
gdt_entries[num].granularity |= gran & 0xf0;
gdt_entries[num].access = access;
}
void gdt_init(void)
{
gdt.limit = sizeof(gdt_entries)*3 - 1;
gdt.base = (uintptr_t)&gdt_entries;
set_entry(0, 0, 0, 0, 0);//Null segment
set_entry(1, 0, 0xffffffff, 0x9a, 0xcf); // kernel code segment
set_entry(2, 0, 0xffffffff, 0x92, 0xcf); // kernel data segment
gdt_flush((uintptr_t)&gdt);
}