/* * 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 #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_16_BIT 0x00 #define GDT_FLAG_32_BIT 0x40 #define GDT_FLAG_64_BIT 0x20 /** @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 uint16_t limit_low; /// Lower 16 bits of base address uint16_t base_low; /// middle 8 bits of base address uint8_t base_middle; /// Access bits uint8_t access; /// Granularity bits uint8_t granularity; /// Higher 8 bits of base address uint8_t 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!) uint16_t limit; /// Address of the table size_t base; } __attribute__ ((packed)) gdt_ptr_t; /// Defines the maximum number of GDT entries #ifdef CONFIG_X86_32 #define GDT_ENTRIES (5+MAX_TASKS) #else // a TSS descriptor is twice larger than a code/data descriptor #define GDT_ENTRIES (5+MAX_TASKS*2) #endif #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 */ void configure_gdt_entry(gdt_entry_t *dest_entry, unsigned long base, unsigned long limit, unsigned char access, unsigned char gran); #ifdef __cplusplus } #endif #endif