metalsvm/arch/x86/include/asm/gdt.h
2011-08-02 15:58:20 +02:00

132 lines
3.6 KiB
C

/*
* Copyright 2010 Stefan Lankes, Chair for Operating Systems,
* RWTH Aachen University
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* This file is part of MetalSVM.
*/
/**
* @file arch/x86/include/asm/gdt.h
* @brief Definitions and functions related to segmentation
* @author Stefan Lankes
*
* This file defines the interface for segmentation as like structures to describe segments.\n
* There are also some other gdt-private functions in the gdt.c file defined.
*/
#ifndef __ARCH_GDT_H__
#define __ARCH_GDT_H__
#include <metalsvm/stddef.h>
#ifdef __cplusplus
extern "C" {
#endif
/// This segment is a data segment
#define GDT_FLAG_DATASEG 0x02
/// This segment is a code segment
#define GDT_FLAG_CODESEG 0x0a
#define GDT_FLAG_TSS 0x09
#define GDT_FLAG_TSS_BUSY 0x02
#define GDT_FLAG_SEGMENT 0x10
/// Privilege level: Ring 0
#define GDT_FLAG_RING0 0x00
/// Privilege level: Ring 1
#define GDT_FLAG_RING1 0x20
/// Privilege level: Ring 2
#define GDT_FLAG_RING2 0x40
/// Privilege level: Ring 3
#define GDT_FLAG_RING3 0x60
/// Segment is present
#define GDT_FLAG_PRESENT 0x80
/**
* @brief Granularity of segment limit
* - set: segment limit unit is 4 KB (page size)
* - not set: unit is bytes
*/
#define GDT_FLAG_4K_GRAN 0x80
/**
* @brief Default operand size
* - set: 32 bit
* - not set: 16 bit
*/
#define GDT_FLAG_32_BIT 0x40
/** @brief Defines a GDT entry
*
* A global descriptor table entry consists of:
* - 32 bit base address (chunkwise embedded into this structure)
* - 20 bit limit
*/
typedef struct {
/// Lower 16 bits of limit range
unsigned short limit_low;
/// Lower 16 bits of base address
unsigned short base_low;
/// middle 8 bits of base address
unsigned char base_middle;
/// Access bits
unsigned char access;
/// Granularity bits
unsigned char granularity;
/// Higher 8 bits of base address
unsigned char base_high;
} __attribute__ ((packed)) gdt_entry_t;
/** @brief defines the GDT pointer structure
*
* This structure tells the address and size of the table.
*/
typedef struct {
/// Size of the table in bytes (not the number of entries!)
unsigned short limit;
/// Address of the table
unsigned int base;
} __attribute__ ((packed)) gdt_ptr_t;
/// Defines the maximum number of GDT entries
#define GDT_ENTRIES (5+MAX_TASKS)
#if GDT_ENTRIES > 8192
#error Too many GDT entries!
#endif
/** @brief Installs the global descriptor table
*
* The installation involves the following steps:
* - set up the special GDT pointer
* - set up the entries in our GDT
* - finally call gdt_flush() in our assembler file
* in order to tell the processor where the new GDT is
* - update the new segment registers
*/
void gdt_install(void);
/** @brief Configures and returns a GDT descriptor with chosen attributes
*
* Just feed this function with address, limit and the flags
* you have seen in idt.h
*
* @return a preconfigured gdt descriptor
*/
gdt_entry_t configure_gdt_entry(unsigned long base, unsigned long limit,
unsigned char access, unsigned char gran);
#ifdef __cplusplus
}
#endif
#endif